Module 1
Exploring the Solar System
Objectives: At the end of this module, you are expected to:
1. Define Astronomy;
2. Give the historical development of Astronomy;
3. Name the prominent ancient and modern astronomers;
4. Give the Sub-branches of Astronomy;
5. Explain the Theories of Solar System formation;
6. Explore the sun as to its parts, significant features, and importance ;
7. Explore the significant features of the major planets;
8. Enumerate the requirements of becoming a major planet; and
9. Explore the Earth and Moon System.
Discussion
Origin of the term Astronomy
The terms "astronomy, astrology, scientific or occult study of heavenly bodies
came from Old French astrenomie .
Moreover, "astronomy and astrology," came from Latin astronomia, and from
Greek astronomia,
which
literally
means
―star-regulating,"
(from astron "star"
+ nomos "arranging, regulating; rule, law,").
https://www.etymonline.com/word/astronomy
Astronomy Defined
Various
and
yet
related
definitions
are
being
given
by
different
authors/astronomers regarding Astronomy. These include the following:
1.
Astronomy is the study of the sun, moon, stars, planets, comets, gas,
galaxies, gas, dust and other non-Earthly bodies and phenomena(space.com)
1
2.
Astronomy is simply "the study of stars, planets and space." –NASA
3.
Astronomy is the study of the sky and everything we see there. It is the oldest
science in the world, and fascinates all kinds of people-young and old,
amateurs and professionals. – Sir Patrick Moore (2005)
4.
Astronomy is the science that encompasses the study of all extraterrestrial
objects and phenomena.- (James Evans, n.d)
Historical Development of Astronomy
Fig 1. The Stonehenge
https://www.astronomytrek.com/wp-content/uploads/2012/11/stoneheng7-300x188.jpg
Ancient civilizations believed their gods lived in the skies, and so early astronomy
was often a mix of detailed observations of the celestial heavens and religion. As well as
a method of trying to divine the will of the gods, astronomy also allowed for more
practical applications, such as predicting the cycle of the seasons for farming, measuring
time and as a directional compass.
By 5000 BCE, ancient peoples had started constructing sun observatories, such
as the Neolithic Era ‗Goseck circle‘, to accurately measure the heavens. The Sumerians
and Babylonians then kept some of the earliest astronomical records yet found,
containing lists of bright stars, names of various constellations, and the movement
of the planets Mercury, Venus, Mars, Jupiter and Saturn.
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By 3,000 BCE the Egyptians had a fairly accurate calendar with the year divided
into 365 days, or 12 ‗months‘ of 30 days and an extra five days added on at the end of
the year as feast days. Other parts of the world, too, were carefully studying the heavens
and in 2137 BC the Chinese recorded the earliest known solar eclipse.
Nevertheless, astronomy still remained closely tied to astrology and it wasn‘t until
600 BCE onwards that Greeks such as Pythagoras, Thales of Miletus, Plato, and
Aristotle helped turn astronomy from mere observation to being a theoretical science
concerned with the structure of the universe. They also used mathematics, geometry and
trigonometry to help explain the reasons for the motions of the Cosmos. Despite
Aristrachus of Samos in 280 BCE then suggesting the first heliocentric theory whereby
it was the Earth and planets which revolved around a stationary Sun at the center of the
Universe, his theory was not generally accepted and Ptolemy further refined the
accepted geocentric model in his 140 A.D masterpiece ‗Almagest,‘ which was used by
the western world for the next 1500 years.
Modern astronomy began to take shape during the time of The Renaissance,
despite fierce protestations by the Church. In 1543, Copernicus published his ―De
Revolutionibus Orbium Coelestium” which used empirical evidence to support a
heliocentric view of the Universe, while Tycho Brahe compiled detailed observations on
the positions of the planets. In around 1605, four years after Brahe‘s death, his assistant
and successor Johannes Kepler observed that the planets moved in elliptical orbits
around the Sun, and so proposed his three laws of planetary motion.
Galileo then added to the growing body of scientific astronomy data by using the
newly invented telescope to make some incredible astronomical observations, including
viewing Jupiter‗s rotating moon system, and noting there were obviously objects in the
heavens which didn‘t revolve around the Earth. By 1687, Sir Isaac Newton invented a
new telescope which used a curved mirror instead of a lens to look further into space,
and published his hugely influential book called ‗Philosophiae Naturalis Principia
Mathematica.‘ Newton agreed that the Earth rotated around the Sun and also
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established the law of universal gravitation, which ushered in a new Age of physics and
Enlightenment.
Since then mankind has done a pretty thorough job mapping the stars, planets
and their moons, and compiling a whole catalogue of astronomical objects and predicting
their nature. In 1798 for instance, Laplace proposed the concept of Black Holes, and by
1817 Charles Messier had compiled a list of 103 deep sky objects he identified as
not comets, and which included nebulae, star clusters, and galaxies.
Astrophysics received a major boost in 1900 when Max Planck invented quantum
mechanics and Einstein‘s two theories of Special and General Relativity changed the
way we viewed the structure of space-time and gravity forever.
By the mid-1900‘s Edwin Hubble had proved that galaxies were separate
systems outside of our own Milky Way and that the Universe was expanding. Mankind
has now walked on the moon, established Space Stations in orbit around the Earth and
discovered hundreds of planets outside of our solar system.
- https://www.astronomytrek.com/history-of-astronomy/
Sub-Branches of Astronomy
Astrobiology
studies the advent and evolution of biological systems in the universe.
Astrophysics
branch of astronomy that deals with the physics of the universe, including the physical
properties of celestial objects, as well as their interactions and behavior.
The sub disciplines of theoretical astrophysics are:
Compact objects
studies very dense matter in white dwarfs and neutron stars and their
effects on environments including accretion.
Physical
cosmology
origin and evolution of the universe as a whole. The study of
cosmology is theoretical astrophysics at its largest scale.
Galactic
astronomy
deals with the structure and components of our galaxy and of other
galaxies.
High energy
astrophysics
studies phenomena occurring at high energies including active
galactic nuclei, supernovae, gamma-ray bursts, quasars, and shocks.
Interstellar
astrophysics
study of the interstellar medium, intergalactic medium and dust.
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Planetary
Science
Extragalactic
astronomy
study of objects (mainly galaxies) outside our galaxy, including
Galaxy formation and evolution.
Stellar astronomy
concerned with Star formation, physical properties, main sequence
life span, variability, stellar evolution and extinction.
Plasma
astrophysics
studies properties of plasma in outer space.
Relativistic
astrophysics
studies effects of special relativity and general relativity in
astrophysical contexts including gravitational waves, gravitational
lensing and black holes.
Solar physics
Sun and its interaction with the remainder of the Solar System and
interstellar space.
study of the planets of the Solar System.
The sub disciplines of Planetary science are:
Atmospheric
science
study of atmospheres and weather.
Exoplanetology
study of various planets outside of the Solar System
Planetary formation
study of formation of planets and moons in the context of the
formation and evolution of the Solar System.
Planetary rings
study of dynamics, stability, and composition of planetary rings
Magnetospheres
study of magnetic fields of planets and moons
Planetary surfaces
study of surface geology of planets and moons
Planetary interiors
study of interior composition of planets and moons
Small Solar System
bodies
study of smallest gravitationally bound bodies, including
asteroids, comets, and Kuiper belt objects
Observation It is the practice of observing celestial objects by using telescopes and other astronomical
al astronomy apparatus.
The sub disciplines of observational astronomy are generally made by the specifications
of the detectors:
1. Radio astronomy(studies celestial objects at radio frequencies) – Above 300 µm
a. The discovery of the cosmic microwave background radiation, regarded
as evidence for the Big Bang theory, was made through radio astronomy.
2. Submillimetre astronomy(conducted at Submillimetre wavelengths (i.e., terahertz
radiation) of the electromagnetic spectrum) – 200 µm to 1 mm
a. Submillimetre observations are used to determine the mechanisms for
the formation and evolution of galaxies and also the process of star
formation from earliest collapse to stellar birth.
3. Infrared astronomy(study of the infrared radiation(heat energy) emitted from
objects in the Universe) – 0.7–350 µm
a. Many objects in the universe which are much too cool and faint to be
detected in visible light, can be detected in the infrared.
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b. It helps to Study the early evolution of galaxies. As a result of the Big
Bang (the tremendous explosion which marked the beginning of our
Universe), the universe is expanding and most of the galaxies within it
are moving away from each other.
c.
Astronomers have discovered that all distant galaxies are moving away
from us and that the farther away they are, the faster they are moving.
This recession of galaxies away from us has an interesting effect on the
light emitted from these galaxies. When an object is moving away from
us, the light that it emits is "redshifted". This means that the
wavelengths get longer and thereby shifted towards the red part of the
spectrum. This effect, called the Doppler effect, is similar to what
happens to sound waves emitted from a moving object. For example, if
you are standing next to a railroad track and a train passes you while
blowing its horn, you will hear the sound change from a higher to a lower
frequency as the train passes you by. As a result of this Doppler effect, at
large redshifts, all of the ultraviolet and much of the visible light from
distant sources is shifted into the infrared part of the spectrum by the
time it reaches our telescopes. This means that the only way to study this
light is in the infrared. Infrared astronomy will provide a great deal of
information on how and when the universe was formed and on what the
early universe was like.
4. Optical astronomy(Visible-light astronomy) – 380–750 nm
a. encompasses a wide variety of observations via telescopes that are
sensitive in the range of visible light (optical telescopes).
5. Ultraviolet astronomy(observation of electromagnetic radiation at ultraviolet
wavelengths) – 10–320 nm
a. Light at these wavelengths is absorbed by the Earth's atmosphere, so
observations at these wavelengths must be performed from the upper
atmosphere or from space.
b. used to discern the chemical composition, densities, and temperatures of
the interstellar medium, and the temperature and composition of hot
young stars.
c.
UV observations can also provide essential information about the
evolution of galaxies.
6. X-ray astronomy(deals with the study of X-ray observation and detection from
astronomical objects.) – 0.01–10 nm
a. X-radiation is absorbed by the Earth's atmosphere, so instruments to
detect X-rays must be taken to high altitude by balloons, sounding
rockets, and satellites.
7. Gamma-ray astronomy( astronomical observation of gamma rays) – Below 0.01
nm
a. Gamma ray telescopes collect and measure individual, high energy
gamma rays from astrophysical sources. These are absorbed by the
atmosphere, requiring that observations are done by high-altitude
balloons or space missions. Gamma rays can be generated by
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supernovae, neutron stars, pulsars and black holes. Gamma ray bursts,
with extremely high energies, have also been detected but have yet to be
identified.
b. Gamma rays in the MeV range are generated in solar flares (and even in
the Earth's atmosphere), but gamma rays in the GeV range do not
originate in our solar system and are important in the study of extrasolar,
and especially extra-galactic astronomy.
8. Cosmic ray astronomy – Cosmic rays, including plasma
a. Cosmic rays are immensely high-energy radiation, mainly originating
outside the Solar System.
b.
They may produce showers of secondary particles that penetrate and
impact the Earth's atmosphere and sometimes even reach the surface.
c.
Composed primarily of high-energy protons and atomic nuclei, they are
of mysterious origin.
d. Cosmic rays attract great interest practically, due to the damage they
inflict on microelectronics and life outside the protection of an
atmosphere and magnetic field, and scientifically, because the energies
of the most energetic ultra-high-energy cosmic rays (UHECRs) have
been observed to approach 3 × 1020 eV, about 40 million times the
energy of particles accelerated by the Large Hadron Collider.
e. Microwave space telescopes have primarily been used to measure
cosmological parameters from the Cosmic Microwave Background.
9. Neutrino astronomy(observes astronomical objects with neutrino detectors in
special observatories) – Neutrinos
a. Neutrinos are created as a result of certain types of radioactive decay, or
nuclear reactions such as those that take place in the Sun, in nuclear
reactors, or when cosmic rays hit atoms.
b. Due to their weak interactions with matter, neutrinos offer a unique
opportunity to observe processes that are inaccessible to optical
telescopes.
c.
The field of neutrino astronomy is still very much in its infancy – the only
confirmed extraterrestrial sources so far are the Sun and supernova
SN1987A.
d. The Moon has also been detected by its absorption of background
neutrinos.
10. Gravitational wave astronomy – Gravitons
a. aims to use gravitational waves (minute distortions of space-time
predicted by Einstein's theory of general relativity) to collect observational
data about objects such as neutron stars and black holes, events such as
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supernovae, and processes including those of the early universe shortly
after the Big Bang.
b. LISA Pathfinder - A new type of telescope to detect gravitational waves;
ripples in space-time generated by colliding neutron stars and black
holes.
Divisions
based on
astronomical
research
Photometry study of how bright celestial objects are when passed through different
filters.
Spectrosco study of the spectra of astronomical objects.
py
Astrometry
study of the position of objects in the sky and their changes of position.
Defines the system of coordinates used and the kinematics of objects in our
galaxy.
Source: http://www.mindmapcharts.com/index.php/gk/astronomy/72-branches-of-astronomy
Theories of Solar System Formation
The Nebula Theory
Based on ideas and observations by Descartes, Kant and Herschel, Pierre
Laplace (1796) put forward the first really scientific theory (summarized in figure 2). A
slowly spinning cloud of gas and dust cooled and collapsed under gravity. As it
collapsed, so it spun faster and flattened along the spin axis. It eventually took on a
lenticular form with equatorial material in free orbit around the central mass. Thereafter
material was left behind as a set of rings within which clumping occurred. Clumps
orbiting at slightly different rates combined to give a protoplanet in each ring. A smaller
version of the scenario, based on the collapse of protoplanets, produced satellite
systems. The central bulk of the original cloud collapsed to form the Sun.
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Fig. 2. The Nebular Theory
https://oup.silverchair-cdn.com/oup/backfile/Content_public/Journal/astrogeo/41/1/10.1046_j.1468-4004.2000.00012.x/1/m_41-1-1.12fig001.gif?Expires=1624547208&Signature=m-uGbjfWqaj5w5oQL846UyV5~EK330tkkPtws7nj6RSIl-IDZSPVVfPW7UD3mpeYvjJGbxFgXVxLjg9GIuR4QXBpggk9M1zOrzAo5fPJ~x5KPJgd6iVEotGZGVMVAm5P2xypwwIko2WQzdpsb4y49FonFRdHcsWEyumgJl7ihXQGT~QOEZa6rbSp5veQXsxL9TZ4CdVxEZUkAqKtD6Bv~tOMOMQ4NBgJaLNXEGNWgb0FD3~ekK9DUEw2pSLxzzpCozYY6nPbV9zI87INxfcZomCIgQtSklwFnXgNQG9xjEhpRVxHi0q~w0TSuTHK1JsoBfB~iPS9P8LMthBtDrw__&Key-PairId=APKAIE5G5CRDK6RD3PGA
An illustration of Laplace's nebula theory. (a) A slowly rotating and collapsing gasand-dust sphere. (b) An oblate spheroid forms as the spin rate increases. (c) The critical
lenticular form. (d) Rings left behind in the equatorial plane. (e) One planet condensing in
each ring.
Source: https://academic.oup.com/astrogeo/article/41/1/1.12/182262
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The Accretion Theory
Fig. 3 Artist Impression of Planetary Formation, courtesy of NASA
https://planethunters.files.wordpress.com/2014/01/formation.jpg?w=479&h=359
Early on, our Solar System was a disk of dust and gas in orbit around the protoSun. The solid materials collided with each other and accreted to form gradually larger
bodies, until the Solar System's four terrestrial planets (Mercury, Venus, Earth, and
Mars) were formed. -Rebecca Fischer (2018)
The Protoplanet Theory
Fig. 4 Artist’s impression of a Mars-sized object crashing into the Earth, starting the
process that eventually created our Moon. Credit: Joe Tucciarone
https://starchild.gsfc.nasa.gov/Images/StarChild/questions/moon_formation.jpg
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According to NASA, about 4.6 billion years ago, as the theory goes, the location of
today‘s Solar System was nothing more than a loose collection of gas and dust — what
we
call
a
nebula.
Then something happened that triggered a pressure change in the center of the cloud.
Perhaps it was a supernova exploding nearby, or a passing star changing the gravity.
Whatever the change, however, the cloud collapsed and created a disc of material.
The center of this disc saw a great increase in pressure that eventually was so
powerful that hydrogen atoms loosely floating in the cloud began to come into contact.
Eventually, they fused and produced helium, kick starting the formation of the Sun.
Moreover, NASA continues that the Sun was a hungry youngster — it ate up 99%
of what was swirling around, but this still left 1% of the disc available for other things.
And
this
is
where
planet
formation
began.
The Solar System was a really messy place at this time, with gas and dust and debris
floating around. But planet formation appears to have happened relatively rapidly. Small
bits of dust and gas began to clump together. The young Sun pushed much of the gas
out to the outer Solar System and its heat evaporated any ice that was nearby.
Over time, this left rockier planets closer to the Sun and gas giants that were
further away. But about four billion or so years ago, an event called the ―late heavy
bombardment‖ resulted in small bodies pelting the bigger members of the Solar System.
We almost lost the Earth when a Mars-sized object crashed into it, as the theory states.
What caused this is still under investigation, but some scientists believe it
was because the gas giants were moving around and perturbing smaller bodies at the
fringe of the Solar System. At any rate, in simple terms, the clumping together of
protoplanets (planets in formation) eventually formed the planets.
https://www.universetoday.com/85761/protoplanet-hypothesis/.
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The Sun
The Sun which is the heart of our
solar system, is a yellow dwarf star, a hot
ball of glowing gases. Its gravity holds the
solar system together, keeping everything
from the biggest planets to the smallest
particles of debris in its orbit. And according
to NASA, it is about 4.5 billion years old.
Electric currents in the Sun generate
a magnetic field that is carried out through
Fig. 5 The Sun
https://solarsystem.nasa.gov/system/resources/detail_files/476_VenusTran
sitApproach1200w.jpg
the solar system by the solar wind—a
stream of electrically charged gas blowing outward from the Sun in all directions.
The connection and interactions between the Sun and Earth drive the seasons,
ocean currents, weather, climate, radiation belts and aurorae. Though it is special to us,
there are billions of stars like our Sun scattered across the Milky Way galaxy.
The Sun has many names in many cultures. The Latin word for Sun is “sol,”
which is the main adjective for all things Sun-related: solar.
The Sun, like others stars, is a ball of gas. In terms of the number of atoms, it
is made of 91.0% hydrogen and 8.9% helium. By mass, the Sun is about 70.6%
hydrogen and 27.4% helium.
Size and Distance
With a radius of 432,168.6 miles (695,508 kilometers), our Sun is not an
especially large star—many are several times bigger—but it is still far more massive than
our home planet: 332,946 Earths match the mass of the Sun. The Sun’s volume
would need 1.3 million Earths to fill it.
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The Sun is 93 million miles (150 million kilometers) from Earth. Its nearest
stellar neighbor is the Alpha Centauri triple star system: Proxima Centauri is 4.24 light
years away, and Alpha Centauri A and B—two stars orbiting each other—are 4.37 light
years away. A light year is the distance light travels in one year, which is equal to
5,878,499,810,000 miles or 9,460,528,400,000 kilometers.
Formation
The Sun and the rest of the solar system formed from a giant, rotating cloud of
gas and dust called a solar nebula about 4.5 billion years ago. As the nebula collapsed
because of its overwhelming gravity, it spun faster and flattened into a disk. Most of the
material was pulled toward the center to form our Sun, which accounts for 99.8% of the
mass of the entire solar system.
Like all stars, the Sun will someday run out of energy. When the Sun starts to die,
it will swell so big that it will engulf Mercury and Venus and maybe even Earth. Scientists
predict the Sun is a little less than halfway through its lifetime and will last another 6.5
billion years before it shrinks down to be a white dwarf.
Orbit and Rotation
The Sun, and everything that orbits it, is located in the Milky Way galaxy. More
specifically, our Sun is in a spiral arm called the Orion Spur that extends outward from
the Sagittarius arm. From there, the Sun orbits the center of the Milky Way Galaxy,
bringing the planets, asteroids, comets and other objects along with it. Our solar system
is moving with an average velocity of 450,000 miles per hour (720,000 kilometers per
hour). But even at this speed, it takes us about 230 million years to make one complete
orbit around the Milky Way.
The Sun rotates as it orbits the center of the Milky Way. Its spin has an axial tilt of
7.25 degrees with respect to the plane of the planets’ orbits. Since the Sun is not a solid
body, different parts of the Sun rotate at different rates. At the equator, the Sun spins
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around once about every 25 days, but at its poles the Sun rotates once on its axis
every 36 Earth days.
Structure
Fig. 6 The Anatomy of the Sun
Credit: NASA/Jenny Mottar
https://www.nasa.gov/sites/default/files/styles/full_width_feature/public/images/655928main
_solar-anatomy-MOS-orig_full.jpg
The Sun's Core - Energy is generated via thermonuclear reactions creating
extreme temperatures deep within the Sun's core. At the core, the temperature is about
27 million degrees Fahrenheit (15 million degrees Celsius), which is sufficient to sustain
thermonuclear fusion. This is a process in which atoms combine to form larger atoms
and in the process release staggering amounts of energy. Specifically, in the Sun’s core,
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hydrogen atoms fuse to make helium. The energy produced in the core powers the Sun
and produces all the heat and light the Sun emits.
The Radiative Zone - Energy moves slowly outward, taking more than 170,000
years to radiate through this layer of the Sun. Energy from the core is carried outward by
radiation, which bounces around the radiative zone,
The Convection Zone - Energy continues to move toward the surface through
convection currents of the heated and cooled gas. The temperature drops below 3.5
million degrees Fahrenheit (2 million degrees Celsius) in the convective zone, where
large bubbles of hot plasma (a soup of ionized atoms) move upwards. The surface of the
Sun—the part we can see—is about 10,000 degrees Fahrenheit (5,500 degrees
Celsius). That's much cooler than the blazing core, but it's still hot enough to make
carbon, like diamonds and graphite, not just melt, but boil.
The Chromosphere - This relatively thin layer of the Sun is sculpted by magnetic
field lines that restrain the electrically charged solar plasma. Occasionally larger plasma
features, called prominences, form and extend far into the very tenuous and hot corona,
sometimes
ejecting
material
away
from
the
Sun.
The Corona - The ionized elements within the corona (or solar atmosphere) glow
in the x-ray and extreme ultraviolet wavelengths. NASA instruments can image the Sun's
corona at these higher energies since the photosphere is quite dim in these wavelength.
Coronal Streamers - The outward flowing plasma of the corona is shaped by magnetic
field lines into tapered forms called coronal streamers, which extend millions of miles into
space.
Surface
The surface of the Sun, the photosphere, is a 300-mile-thick (500-kilometerthick) region, from which most of the Sun's radiation escapes outward. This is not a solid
surface like the surfaces of planets. Instead, this is the outer layer of the gassy star.
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We see radiation from the photosphere as sunlight when it reaches Earth about eight
minutes after it leaves the Sun. The temperature of the photosphere is about
10,000 degrees Fahrenheit (5,500 degrees Celsius).
Atmosphere
Above the photosphere lie the tenuous chromosphere and the corona (crown),
which make up the thin solar atmosphere. This is where we see features such as
sunspots and solar flares.
Visible light from these top regions is usually too weak to be seen against the
brighter photosphere, but during total solar eclipses, when the moon covers the
photosphere, the chromosphere looks like a red rim around the Sun, while the corona
forms a beautiful white crown with plasma streamers narrowing outward, forming shapes
that look like flower petals.
Strangely, the temperature in the Sun's atmosphere increases with altitude,
reaching as high as 3.5 million degrees Fahrenheit (2 million degrees Celsius). The
source of coronal heating has been a scientific mystery for more than 50 years.
Potential for Life
The Sun itself is not a good place for living things, with its hot, energetic mix of
gases and plasma. But the Sun has made life on Earth possible, providing warmth as
well as energy that organisms like plants use to form the basis of many food chains.
Moons
The Sun and other stars don't have moons; instead, they have planets and their
moons, along with asteroids, comets, and other objects.
Rings
The Sun does not have rings.
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Magnetosphere
The electric currents in the Sun generate a complex magnetic field that extends
out into space to form the interplanetary magnetic field. The volume of space controlled
by the Sun's magnetic field is called the heliosphere.
The Sun's magnetic field is carried out through the solar system by the solar
wind—a stream of electrically charged gas blowing outward from the Sun in all
directions. Since the Sun rotates, the magnetic field spins out into a large rotating spiral,
known as the Parker spiral.
The Sun doesn't behave the same way all the time. It goes through phases of its
own solar cycle. Approximately every 11 years, the Sun‘s geographic poles change their
magnetic polarity. When this happens, the Sun's photosphere, chromosphere and
corona undergo changes from quiet and calm to violently active. The height of the Sun‘s
activity, known as solar maximum, is a time of solar storms: sunspots, solar flares and
coronal mass ejections. These are caused by irregularities in the Sun's magnetic field
and can release huge amounts of energy and particles, some of which reach us here on
Earth. This space weather can damage satellites, corrode pipelines and affect power
grids.
Source: https://solarsystem.nasa.gov/solar-system/sun/in-depth/
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What is a Planet?
The International Astronomical Union (IAU) ruled in August 2006 that to be a planet
an object must meet three criteria:
1. It must have enough mass and gravity to gather itself into a sphere
2. It must orbit the sun
3. It must reign supreme in its own orbit, having ―cleared the neighborhood‖ of other
competing bodies
Source:https://courses.lumenlearning.com/atd-fscj-introastronomy/chapter/what-is-a- planet/
The Major Planets
The major planets are classified into: terrestrial or inner planets (Mercury, Venus,
Mars and Earth) and the outer planets/gas giants and ice giants. ( Jupiter, Saturn,
Uranus, and Neptune.
Mercury
Figure 7. Mercury's Caloris Basin
NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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Mercury is the smallest planet in our solar system and nearest to the Sun,
Mercury is only slightly larger than Earth's Moon. From the surface of Mercury, the Sun
would appear more than three times as large as it does when viewed from Earth, and the
sunlight would be as much as seven times brighter. Despite its proximity to the Sun,
Mercury is not the hottest planet in our solar system – that title belongs to nearby Venus,
thanks to its dense atmosphere. But Mercury is the fastest planet, zipping around the
Sun every 88 Earth days. Mercury is appropriately named for the swiftest of the ancient
Roman gods.
Size and Distance
With a radius of 1,516 miles (2,440 kilometers), Mercury is a little more than 1/3
the width of Earth.
From an average distance of 36 million miles (58 million kilometers), Mercury is
0.4 astronomical units away from the Sun. One astronomical unit (abbreviated as
AU), is the distance from the Sun to Earth. From this distance, it takes sunlight 3.2
minutes to travel from the Sun to Mercury.
Orbit and Rotation
Mercury's highly eccentric, egg-shaped orbit takes the planet as close as 29
million miles (47 million kilometers) and as far as 43 million miles (70 million
kilometers) from the Sun. It speeds around the Sun every 88 days, traveling through
space at nearly 29 miles (47 kilometers) per second, faster than any other planet.
Mercury spins slowly on its axis and completes one rotation every 59 Earth
days. But when Mercury is moving fastest in its elliptical orbit around the Sun (and it is
closest to the Sun), each rotation is not accompanied by a sunrise and sunset like it is on
most other planets. The morning Sun appears to rise briefly, set and rise again from
some parts of the planet's surface. The same thing happens in reverse at sunset for
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other parts of the surface. One Mercury solar day (one full day-night cycle) equals
176 Earth days—just over two years on Mercury.
Mercury's axis of rotation is tilted just 2 degrees with respect to the plane of its
orbit around the Sun. That means it spins nearly perfectly upright and so does not
experience seasons like many other planets do.
Structure
Mercury is the second densest planet, after Earth. It has a large metallic core
with a radius of about 1,289 miles (2,074 kilometers), about 85 percent of the
planet's radius. There is evidence that it is partly molten, or liquid. Mercury's outer shell,
comparable to Earth's outer shell (called the mantle and crust), is only about 400
kilometers (250 miles) thick.
Formation
Mercury formed about 4.5 billion years ago when gravity pulled swirling gas and
dust together to form this small planet nearest the Sun. Like its fellow terrestrial planets,
Mercury has a central core, a rocky mantle and a solid crust.
Surface
Mercury's surface resembles that of Earth's moon, scarred by many impact
craters resulting from collisions with meteoroids and comets. Craters and features on
Mercury are named after famous deceased artists, musicians or authors, including
children's author Dr. Seuss and dance pioneer Alvin Ailey.
Very large impact basins, including Caloris (960 miles or 1,550 kilometers in
diameter) and Rachmaninoff (190 miles, or 306 kilometers in diameter), were
created by asteroid impacts on the planet's surface early in the solar system's history.
While there are large areas of smooth terrain, there are also cliffs, some hundreds of
miles long and soaring up to a mile high. They rose as the planet's interior cooled and
contracted over the billions of years since Mercury formed.
20
Most of Mercury's surface would appear greyish-brown to the human eye. The
bright streaks are called "crater rays." They are formed when an asteroid or comet
strikes the surface. The tremendous amount of energy that is released in such an impact
digs a big hole in the ground, and also crushes a huge amount of rock under the point of
impact. Some of this crushed material is thrown far from the crater and then falls to the
surface, forming the rays. Fine particles of crushed rock are more reflective than large
pieces, so the rays look brighter. The space environment—dust impacts and solar-wind
particles—causes the rays to darken with time.
Temperatures on the surface of Mercury are extreme, both hot and cold.
During the day, temperatures on Mercury's surface can reach 800 degrees Fahrenheit
(430 degrees Celsius). Because the planet has no atmosphere to retain that heat,
nighttime temperatures on the surface can drop to minus 290 degrees Fahrenheit
(minus 180 degrees Celsius).
Mercury may have water ice at its north and south poles inside deep craters, but
only in regions of permanent shadow. There it could be cold enough to preserve water
ice despite the high temperatures on sunlit parts of the planet.
Atmosphere
Instead of an atmosphere, Mercury possesses a thin exosphere made up of
atoms blasted off the surface by the solar wind and striking meteoroids. Mercury's
exosphere is composed mostly of oxygen, sodium, hydrogen, helium and
potassium.
Magnetosphere
Mercury's magnetic field is offset relative to the planet's equator. Though
Mercury's magnetic field at the surface has just one percent the strength of Earth's, it
interacts with the magnetic field of the solar wind to sometimes create intense magnetic
tornadoes that funnel the fast, hot solar wind plasma down to the surface of the planet.
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When the ions strike the surface, they knock off neutrally charged atoms and send them
on a loop high into the sky.
Moons
Mercury has no moon.
Potential for Life
Mercury's environment is not conducive to life as we know it. The temperatures and solar
radiation that characterize this planet are most likely too extreme for organisms to adapt
to.
Venus
Figure 8. The Planet Venus
https://solarsystem.nasa.gov/system/news_items/main_images/1519_688_Venus_1200.jpg
Venus is the second planet from the Sun and our closest planetary neighbor.
Similar in structure and size to Earth, Venus spins slowly in the opposite direction
from most planets. Its thick atmosphere traps heat in a runaway greenhouse
effect, making it the hottest planet in our solar system with surface temperatures
hot enough to melt lead. Glimpses below the clouds reveal volcanoes and deformed
mountains.
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Venus is named for the ancient Roman goddess of love and beauty, who was
known as Aphrodite to the Ancient Greeks.
Size and Distance
With a radius of 3,760 miles (6,052 kilometers), Venus is roughly the same size
as Earth — just slightly smaller.
From an average distance of 67 million miles (108 million kilometers), Venus is 0.7
astronomical units away from the Sun. One astronomical unit (abbreviated as AU), is
the distance from the Sun to Earth. It takes sunlight 6 minutes to travel from the Sun
to Venus.
Orbit and Rotation
Venus' rotation and orbit are unusual in several ways. Venus is one of just two
planets that rotate from east to west. Only Venus and Uranus have this "backwards"
rotation. It completes one rotation in 243 Earth days — the longest day of any planet
in our solar system, even longer than a whole year on Venus. But the Sun doesn't rise
and set each "day" on Venus like it does on most other planets. On Venus, one
day-night cycle takes 117 Earth days because Venus rotates in the direction
opposite of its orbital revolution around the Sun.
Venus makes a complete orbit around the Sun (a year in Venusian time) in
225 Earth days or slightly less than two Venusian day-night cycles. Its orbit around
the Sun is the most circular of any planet — nearly a perfect circle. Other planet's orbits
are more elliptical, or oval-shaped.
With an axial tilt of just 3 degrees, Venus spins nearly upright, and so does not
experience noticeable seasons.
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Structure
Venus is in many ways similar to Earth in its structure. It has an iron core that is
approximately 2,000 miles (3,200 kilometers) in radius. Above that is a mantle made
of hot rock slowly churning due to the planet's interior heat. The surface is a thin crust of
rock that bulges and moves as Venus' mantle shifts and creates volcanoes.
Formation
When the solar system settled into its current layout about 4.5 billion years ago,
Venus formed when gravity pulled swirling gas and dust together to form the second
planet from the Sun. Like its fellow terrestrial planets, Venus has a central core, a rocky
mantle and a solid crust.
Surface
From space, Venus is bright white because it is covered with clouds that reflect
and scatter sunlight. At the surface, the rocks are different shades of grey, like rocks on
Earth, but the thick atmosphere filters the sunlight so that everything would look orange if
you were standing on Venus.
Venus has mountains, valleys, and tens of thousands of volcanoes. The highest
mountain on Venus, Maxwell Montes, is 20,000 feet high (8.8 kilometers), similar to
the highest mountain on Earth, Mount Everest. The landscape is dusty, and surface
temperatures reach a scalding 880 degrees Fahrenheit (471 degrees Celsius).
It is thought that Venus was completely resurfaced by volcanic activity 300 to 500
million years ago. Venus has two large highland areas: Ishtar Terra, about the size of
Australia, in the north polar region; and Aphrodite Terra, about the size of South
America, straddling the equator and extending for almost 6,000 miles (10,000
kilometers).
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Venus is covered in craters, but none are smaller than 0.9 to 1.2 miles (1.5 to 2
kilometers) across. Small meteoroids burn up in the dense atmosphere, so only large
meteoroids reach the surface and create impact craters.
Almost all the surface features of Venus are named for noteworthy Earth women
— both mythological and real. A volcanic crater is named for Sacajawea, the Native
American woman who guided Lewis and Clark's exploration. A deep canyon is named
for Diana, Roman goddess of the hunt.
Atmosphere
Venus' atmosphere consists mainly of carbon dioxide, with clouds of sulfuric
acid droplets. The thick atmosphere traps the Sun's heat, resulting in surface
temperatures higher than 880 degrees Fahrenheit (470 degrees Celsius). The
atmosphere has many layers with different temperatures. At the level where the clouds
are, about 30 miles up from the surface, it's about the same temperature as on the
surface of the Earth.
As Venus moves forward in its solar orbit while slowly rotating backwards on its
axis, the top level of clouds zips around the planet every four Earth days, driven by
hurricane-force winds traveling at about 224 miles (360 kilometers) per hour.
Atmospheric lightning bursts light up these quick-moving clouds. Speeds within the
clouds decrease with cloud height, and at the surface are estimated to be just a few
miles per hour.
On the ground, it would look like a very hazy, overcast day on Earth. And the
atmosphere is so heavy it would feel like you were 1 mile (1.6 kilometers) deep
underwater.
Magnetosphere
Even though Venus is similar in size to the Earth and has a similarly-sized iron
core, Venus' magnetic field is much weaker than the Earth's due to Venus' slow
rotation.
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Rings
Venus has no rings.
Moons
Venus has no moons.
Potential for Life
No human has visited Venus, but the spacecraft that have been sent to the
surface of Venus do not last very long there. Venus' high surface temperatures overheat
electronics in spacecraft in a short time, so it seems unlikely that a person could survive
for long on the Venusian surface.
There is speculation about life existing in Venus' distant past, as well as questions
about the possibility of life in the top cloud layers of Venus' atmosphere, where the
temperatures are less extreme.
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The Earth
Fig 8. The Planet Earth
Source: NOAA/NASA EPIC Team
https://solarsystem.nasa.gov/resources/2332/as-the-world-turns/?category=planets_earth
https://solarsystem.nasa.gov/https://solarsystem.nasa.gov/system/resources/detail_files/2332_earth_dscovr_apr T
Our home planet is the third planet from the Sun, and the only place we know of
so far that’s inhabited by living things.
While Earth is only the fifth largest planet in the solar system, it is the only world in
our solar system with liquid water on the surface. Just slightly larger than nearby Venus,
Earth is the biggest of the four planets closest to the Sun, all of which are made of rock
and metal.
The name Earth is at least 1,000 years old. All of the planets, except for Earth,
were named after Greek and Roman gods and goddesses. However, the name Earth is
a Germanic word, which simply means “the ground.”
From an average distance of 93 million miles (150 million kilometers), Earth
is exactly one astronomical unit away from the Sun because one astronomical unit
(abbreviated as AU), is the distance from the Sun to Earth. This unit provides an easy
way to quickly compare planets' distances from the Sun.
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It takes about eight minutes for light from the Sun to reach our planet.
Orbit and Rotation
As Earth orbits the Sun, it completes one rotation every 23.9 hours. It takes
365.25 days to complete one trip around the Sun. That extra quarter of a day
presents a challenge to our calendar system, which counts one year as 365 days. To
keep our yearly calendars consistent with our orbit around the Sun, every four years we
add one day. That day is called a leap day, and the year it's added to is called a leap
year.
Earth's axis of rotation is tilted 23.4 degrees with respect to the plane of Earth's
orbit around the Sun. This tilt causes our yearly cycle of seasons. During part of the year,
the northern hemisphere is tilted toward the Sun and the southern hemisphere is tilted
away. With the Sun higher in the sky, solar heating is greater in the north producing
summer there. Less direct solar heating produces winter in the south. Six months later,
the situation is reversed. When spring and fall begin, both hemispheres receive roughly
equal amounts of heat from the Sun.
Structure
Earth is composed of four main layers, starting with an inner core at the planet's
center, enveloped by the outer core, mantle and crust.
The inner core is a solid sphere made of iron and nickel metals about 759
miles (1,221 kilometers) in radius. There the temperature is as high as 9,800 degrees
Fahrenheit (5,400 degrees Celsius). Surrounding the inner core is the outer core. This
layer is about 1,400 miles (2,300 kilometers) thick, made of iron and nickel fluids.
In between the outer core and crust is the mantle, the thickest layer. This hot,
viscous mixture of molten rock is about 1,800 miles (2,900 kilometers) thick and
has the consistency of caramel. The outermost layer, Earth's crust, goes about 19 miles
(30 kilometers) deep on average on land. At the bottom of the ocean, the crust is
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thinner and extends about 3 miles (5 kilometers) from the sea floor to the top of
the mantle.
Formation
When the solar system settled into its current layout about 4.5 billion years ago,
Earth formed when gravity pulled swirling gas and dust in to become the third planet
from the Sun. Like its fellow terrestrial planets, Earth has a central core, a rocky mantle
and a solid crust.
Surface
Like Mars and Venus, Earth has volcanoes, mountains and valleys. Earth's
lithosphere, which includes the crust (both continental and oceanic) and the upper
mantle, is divided into huge plates that are constantly moving. For example, the North
American plate moves west over the Pacific Ocean basin, roughly at a rate equal to the
growth of our fingernails. Earthquakes result when plates grind past one another, ride up
over one another, collide to make mountains, or split and separate.
Earth's global ocean, which covers nearly 70 percent of the planet's surface, has
an average depth of about 2.5 miles (4 kilometers) and contains 97 percent of Earth's
water. Almost all of Earth's volcanoes are hidden under these oceans. Hawaii's Mauna
Kea volcano is taller from base to summit than Mount Everest, but most of it is
underwater. Earth's longest mountain range is also underwater, at the bottom of the
Arctic and Atlantic oceans. It is four times longer than the Andes, Rockies and Himalayas
combined.
Atmosphere
Near the surface, Earth has an atmosphere that consists of 78 percent nitrogen,
21 percent oxygen, and 1 percent other gases such as argon, carbon dioxide and
neon. The atmosphere affects Earth's long-term climate and short-term local weather
and shields us from much of the harmful radiation coming from the Sun. It also protects
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us from meteoroids, most of which burn up in the atmosphere, seen as meteors in the
night sky, before they can strike the surface as meteorites.
Magnetosphere
Our planet's rapid rotation and molten nickel-iron core give rise to a magnetic
field, which the solar wind distorts into a teardrop shape in space. (The solar wind is a
stream of charged particles continuously ejected from the Sun.) When charged
particles from the solar wind become trapped in Earth's magnetic field, they
collide with air molecules above our planet's magnetic poles. These air molecules
then begin to glow and cause aurorae, or the northern and southern lights.
The magnetic field is what causes compass needles to point to the North Pole
regardless of which way you turn. But the magnetic polarity of Earth can change, flipping
the direction of the magnetic field. The geologic record tells scientists that a magnetic
reversal takes place about every 400,000 years on average, but the timing is very
irregular. As far as we know, such a magnetic reversal doesn't cause any harm to life on
Earth, and a reversal is very unlikely to happen for at least another thousand years. But
when it does happen, compass needles are likely to point in many different directions for
a few centuries while the switch is being made. And after the switch is completed, they
will all point south instead of north.
Rings
Earth has no rings.
Moons
Earth is the only planet that has a single moon.
Potential for Life
Earth has a very hospitable temperature and mix of chemicals that have made life
possible here. Most notably, Earth is unique in that most of our planet is covered in
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water, since the temperature allows liquid water to exist for extended periods of time.
Earth's vast oceans provided a convenient place for life to begin about 3.8 billion years
ago. Some of the features of our planet that make it great for sustaining life are changing
due to the ongoing effects of climate change.
Source: https://solarsystem.nasa.gov/planets/earth/in-depth/
Mars
Fig. 11 The Planet Mars
https://mars.nasa.gov/system/content_pages/main_images/418_marsglobe.jpg
Mars was named by the ancient Romans for their god of war because its reddish
color was reminiscent of blood. Other civilizations also named the planet for this
attribute; for example, the Egyptians called it "Her Desher," meaning "the red one." Even
today, it is frequently called the "Red Planet" because iron minerals in the Martian dirt
oxidize, or rust, causing the surface to look red.
Size and Distance
With a radius of 2,106 miles (3,390 kilometers), Mars is about half the size of
Earth.
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From an average distance of 142 million miles (228 million kilometers), Mars is
1.5 astronomical units away from the Sun. One astronomical unit (abbreviated as
AU), is the distance from the Sun to Earth. From this distance, it takes sunlight 13
minutes to travel from the Sun to Mars.
Orbit and Rotation
As Mars orbits the Sun, it completes one rotation every 24.6 hours, which is
very similar to one day on Earth (23.9 hours). Martian days are called sols—short for
"solar day." A year on Mars lasts 669.6 sols, which is the same as 687 Earth days.
Mars' axis of rotation is tilted 25 degrees with respect to the plane of its orbit
around the Sun. This is another similarity with Earth, which has an axial tilt of 23.4
degrees. Like Earth, Mars has distinct seasons, but they last longer than seasons here
on Earth since Mars takes longer to orbit the Sun (because it's farther away). And while
here on Earth the seasons are evenly spread over the year, lasting 3 months (or one
quarter of a year), on Mars the seasons vary in length because of Mars' elliptical, eggshaped orbit around the Sun.
Spring in the northern hemisphere (autumn in the southern) is the longest season
at 194 sols. Autumn in the northern hemisphere (spring in the southern) is the shortest at
142 days. Northern winter/southern summer is 154 sols, and northern summer/southern
winter is 178 sols.
Structure
Mars has a dense core at its center between 930 and 1,300 miles (1,500 to
2,100 kilometers) in radius. It's made of iron, nickel, and sulfur. Surrounding the
core is a rocky mantle between 770 and 1,170 miles (1,240 to 1,880 kilometers)
thick, and above that, a crust made of iron, magnesium, aluminum, calcium, and
potassium. This crust is between 6 and 30 miles (10 to 50 kilometers) deep.
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Formation
When the solar system settled into its current layout about 4.5 billion years ago,
Mars formed when gravity pulled swirling gas and dust in to become the fourth planet
from the Sun. Mars is about half the size of Earth, and like its fellow terrestrial planets, it
has a central core, a rocky mantle, and a solid crust.
Surface
The Red Planet is actually many colors. At the surface, we see colors such as
brown, gold, and tan. The reason Mars looks reddish is due to oxidization—or
rusting—of iron in the rocks, regolith (Martian “soil”), and dust of Mars. This dust
gets kicked up into the atmosphere and from a distance makes the planet appear mostly
red.
Interestingly, while Mars is about half the diameter of Earth, its surface has nearly
the same area as Earth’s dry land. Its volcanoes, impact craters, crustal movement, and
atmospheric conditions such as dust storms have altered the landscape of Mars over
many years, creating some of the solar system's most interesting topographical features.
A large canyon system called Valles Marineris is long enough to stretch from
California to New York—more than 3,000 miles (4,800 kilometers). This Martian canyon
is 200 miles (320 kilometers) at its widest and 4.3 miles (7 kilometers) at its deepest.
That's about 10 times the size of Earth's Grand Canyon.
Mars is home to the largest volcano in the solar system, Olympus Mons. It's
three times taller than Earth's Mt. Everest with a base the size of the state of New
Mexico.
Mars appears to have had a watery past, with ancient river valley networks,
deltas, and lakebeds, as well as rocks and minerals on the surface that could only have
formed in liquid water. Some features suggest that Mars experienced huge floods about
3.5 billion years ago.
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There is water on Mars today, but the Martian atmosphere is too thin for liquid
water to exist for long on the surface. Today, water on Mars is found in the form of waterice just under the surface in the Polar Regions as well as in briny (salty) water, which
seasonally flows down some hillsides and crater walls.
Atmosphere
Mars has a thin atmosphere made up mostly of carbon dioxide, nitrogen,
and argon gases. To our eyes, the sky would be hazy and red because of suspended
dust instead of the familiar blue tint we see on Earth. Mars' sparse atmosphere doesn't
offer much protection from impacts by such objects as meteorites, asteroids, and
comets.
The temperature on Mars can be as high as 70 degrees Fahrenheit (20
degrees Celsius) or as low as about -225 degrees Fahrenheit (-153 degrees
Celsius). And because the atmosphere is so thin, heat from the Sun easily escapes this
planet. If you were to stand on the surface of Mars on the equator at noon, it would feel
like spring at your feet (75 degrees Fahrenheit or 24 degrees Celsius) and winter at your
head (32 degrees Fahrenheit or 0 degrees Celsius).
Occasionally, winds on Mars are strong enough to create dust storms that cover
much of the planet. After such storms, it can be months before all of the dust settles.
Magnetosphere
Mars has no global magnetic field today, but areas of the Martian crust in the
southern hemisphere are highly magnetized, indicating traces of a magnetic field from 4
billion years ago.
Rings
Mars has no rings. However, in 50 million years when Phobos crashes into Mars or
breaks apart, it could create a dusty ring around the Red Planet.
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Moons
Mars' largest moon Phobos as seen by Mars
Reconnaissance Orbiter in 2008. Credit:
NASA/JPL-Caltech/University of Arizona | ›
Mars has two small moons, Phobos and Deimos, that may be captured asteroids.
They're potato-shaped because they have too little mass for gravity to make them
spherical.
The moons get their names from the horses that pulled the chariot of the Greek
god of war, Ares. Phobos, the innermost and larger moon, is heavily cratered, with deep
grooves on its surface. It is slowly moving towards Mars and will crash into the planet or
break apart in about 50 million years. Deimos is about half as big as Phobos and orbits
two and a half times farther away from Mars. Oddly-shaped Deimos is covered in loose
dirt that often fills the craters on its surface, making it appear smoother than pockmarked
Phobos.
Potential for Life
Scientists don't expect to find living things currently thriving on Mars. Instead,
they're looking for signs of life that existed long ago, when Mars was warmer and
covered with water.
Source: https://solarsystem.nasa.gov/planets/mars/in-depth/
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Jupiter
The Planet Jupiter
https://toptenscience.com/wp-content/uploads/2019/03/planet-jupiter.jpg
Jupiter is the fifth planet from our Sun and is, by far, the largest planet in the solar
system – more than twice as massive as all the other planets combined. Jupiter's stripes
and swirls are actually cold, windy clouds of ammonia and water, floating in an
atmosphere of hydrogen and helium. Jupiter‘s iconic Great Red Spot is a giant storm
bigger than Earth that has raged for hundreds of years.
Jupiter is surrounded by dozens of moons. Jupiter also has several rings, but
unlike the famous rings of Saturn, Jupiter‘s rings are very faint and made of dust, not ice.
Exploration
Nine spacecraft have studied Jupiter up close. NASA's Juno spacecraft is
currently studying the gas giant planet from orbit. The spacecraft, which arrived at Jupiter
in July 2016, is the first to study the planet's mysterious, cloud-shrouded interior.
Scientists also use the Earth-orbiting Hubble Space Telescope and ground-based
telescopes to regularly check in on Jupiter.
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Pioneer 10 was the first spacecraft to fly past Jupiter. It was followed by Pioneer
11, Voyager 1 and Voyager 2 flybys. NASA's Galileo mission was first to orbit
Jupiter and to send an atmospheric probe into the stormy clouds. The
international Ulysses mission used Jupiter's powerful gravity to hurl itself into orbital
passes
of
the
Sun's
northern
and
southern
poles.
Both Cassini and New
Horizons studied Jupiter as they hurtled on to their main science targets — Saturn for
Cassini and Pluto and the Kuiper Belt for New Horizons.
Two new missions are in the works to make close studies of Jupiter's moons
NASA's Europa Clipper and ESA's JUpiter ICy Moons Explorer (JUICE).
Jupiter holds a unique place in the history of space exploration. In 1610,
astronomer Galileo Galilei used a new invention called the telescope to look at Jupiter
and discovered the first moons known to exist beyond Earth. The discovery ended
incorrect, ancient belief that everything, including the Sun and other planets, orbited the
Earth.
Size and Distance
With a radius of 43,440.7 miles (69,911 kilometers), Jupiter is 11 times wider
than Earth. If Earth were the size of a nickel, Jupiter would be about as big as a
basketball.
From an average distance of 484 million miles (778 million kilometers), Jupiter is
5.2 astronomical units away from the Sun. One astronomical unit (abbreviated as
AU), is the distance from the Sun to Earth. From this distance, it takes sunlight 43
minutes to travel from the Sun to Jupiter.
Orbit and Rotation
Jupiter has the shortest day in the solar system. One day on Jupiter takes only
about 10 hours (the time it takes for Jupiter to rotate or spin around once), and
Jupiter makes a complete orbit around the Sun (a year in Jovian time) in about 12
Earth years (4,333 Earth days).
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Its equator is tilted with respect to its orbital path around the Sun by just 3
degrees. This means Jupiter spins nearly upright and does not have seasons as extreme
as other planets do.
Structure
The composition of Jupiter is similar to that of the Sun—mostly hydrogen
and helium. Deep in the atmosphere, pressure and temperature increase,
compressing the hydrogen gas into a liquid. This gives Jupiter the largest ocean
in the solar system—an ocean made of hydrogen instead of water. Scientists think
that, at depths perhaps halfway to the planet's center, the pressure becomes so great
that electrons are squeezed off the hydrogen atoms, making the liquid electrically
conducting like metal. Jupiter's fast rotation is thought to drive electrical currents in this
region, generating the planet's powerful magnetic field. It is still unclear if, deeper down,
Jupiter has a central core of solid material or if it may be a thick, super-hot and dense
soup. It could be up to 90,032 degrees Fahrenheit (50,000 degrees Celsius) down there,
made mostly of iron and silicate minerals (similar to quartz).
Formation
Jupiter took shape when the rest of the solar system formed about 4.5 billion
years ago, when gravity pulled swirling gas and dust in to become this gas giant. Jupiter
took most of the mass left over after the formation of the Sun, ending up with more than
twice the combined material of the other bodies in the solar system. In fact, Jupiter has
the same ingredients as a star, but it did not grow massive enough to ignite.
About 4 billion years ago, Jupiter settled into its current position in the outer solar
system, where it is the fifth planet from the Sun.
Surface
As a gas giant, Jupiter doesn‘t have a true surface. The planet is mostly swirling
gases and liquids. While a spacecraft would have nowhere to land on Jupiter, it wouldn‘t
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be able to fly through unscathed either. The extreme pressures and temperatures deep
inside the planet crush, melt and vaporize spacecraft trying to fly into the planet.
Atmosphere
Jupiter's appearance is a tapestry of colorful cloud bands and spots. The gas
planet likely has three distinct cloud layers in its "skies" that, taken together, span about
44 miles (71 kilometers). The top cloud is probably made of ammonia ice, while the
middle layer is likely made of ammonium hydrosulfide crystals. The innermost
layer may be made of water ice and vapor.
The vivid colors you see in thick bands across Jupiter may be plumes of sulfur
and phosphorus-containing gases rising from the planet's warmer interior. Jupiter's fast
rotation—spinning once every 10 hours—creates strong jet streams, separating its
clouds into dark belts and bright zones across long stretches.
With no solid surface to slow them down, Jupiter's spots can persist for many
years. Stormy Jupiter is swept by over a dozen prevailing winds, some reaching up to
335 miles per hour (539 kilometers per hour) at the equator. The Great Red Spot, a
swirling oval of clouds twice as wide as Earth, has been observed on the giant planet for
more than 300 years. More recently, three smaller ovals merged to form the Little Red
Spot, about half the size of its larger cousin. Scientists do not yet know if these ovals and
planet-circling bands are shallow or deeply rooted to the interior.
Magnetosphere
The Jovian magnetosphere is the region of space influenced by Jupiter's powerful
magnetic field. It balloons 600,000 to 2 million miles (1 to 3 million kilometers) toward the
Sun (seven to 21 times the diameter or Jupiter itself) and tapers into a tadpole-shaped
tail extending more than 600 million miles (1 billion kilometers) behind Jupiter, as far as
Saturn's orbit. Jupiter's enormous magnetic field is 16 to 54 times as powerful as
that of the Earth. It rotates with the planet and sweeps up particles that have an electric
charge. Near the planet, the magnetic field traps swarms of charged particles and
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accelerates them to very high energies, creating intense radiation that bombards the
innermost moons and can damage spacecraft.
Jupiter's magnetic field also causes some of the solar system's most spectacular
aurorae at the planet's poles.
Rings
Discovered in 1979 by NASA's Voyager 1 spacecraft, Jupiter's rings were a
surprise, as they are composed of small, dark particles and are difficult to see
except when backlit by the Sun. Data from the Galileo spacecraft indicate that Jupiter's
ring system may be formed by dust kicked up as interplanetary meteoroids smash into
the giant planet's small innermost moons.
Moons
With four large moons and many smaller moons, Jupiter forms a kind of miniature
solar system. Jupiter has 53 confirmed moons and 26 provisional moons awaiting
confirmation of discovery. Moons are named after they are confirmed.
Jupiter's four largest moons—Io, Europa, Ganymede and Callisto—were first
observed by the astronomer Galileo Galilei in 1610 using an early version of the
telescope. These four moons are known today as the Galilean satellites, and they're
some of the most fascinating destinations in our solar system. Io is the most volcanically
active body in the solar system. Ganymede is the largest moon in the solar system
(even bigger than the planet Mercury). Callisto’s very few small craters indicate a small
degree of current surface activity. A liquid-water ocean with the ingredients for life may
lie beneath the frozen crust of Europa, making it a tempting place to explore.
Potential for Life
Jupiter‘s environment is probably not conducive to life as we know it. The
temperatures, pressures and materials that characterize this planet are most likely too
extreme and volatile for organisms to adapt to.
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While planet Jupiter is an unlikely place for living things to take hold, the same is
not true of some of its many moons. Europa is one of the likeliest places to find life
elsewhere in our solar system. There is evidence of a vast ocean just beneath its icy
crust, where life could possibly be supported.
Source: https://solarsystem.nasa.gov/planets/jupiter/in-depth/
Saturn
The Planet Saturn
Photojournal: PIA01364
Source: NASA/JPL
41
Saturn is the sixth planet from the Sun and the second largest planet in our solar
system. Adorned with a dazzling system of icy rings, Saturn is unique among the
planets. It is not the only planet to have rings, but none are as spectacular or as complex
as Saturn's. Like fellow gas giant Jupiter, Saturn is a massive ball made mostly of
hydrogen and helium.
Surrounded by more than 60 known moons, Saturn is home to some of the most
fascinating landscapes in our solar system. From the jets of water that spray from
Enceladus to the methane lakes on smoggy Titan, the Saturn system is a rich source of
scientific discovery and still holds many mysteries.
The farthest planet from Earth discovered by the unaided human eye, Saturn has
been known since ancient times. The planet is named for the Roman god of
agriculture and wealth, who was also the father of Jupiter.
Size and Distance
With a radius of 36,183.7 miles (58,232 kilometers), Saturn is 9 times wider
than Earth. If Earth were the size of a nickel, Saturn would be about as big as a
volleyball.
From an average distance of 886 million miles (1.4 billion kilometers), Saturn is
9.5 astronomical units away from the Sun. One astronomical unit (abbreviated as
AU), is the distance from the Sun to Earth. From this distance, it takes sunlight 80
minutes to travel from the Sun to Saturn.
Orbit and Rotation
Saturn has the second-shortest day in the solar system. One day on Saturn takes
only 10.7 hours (the time it takes for Saturn to rotate or spin around once), and Saturn
makes a complete orbit around the Sun (a year in Saturnian time) in about 29.4 Earth
years (10,756 Earth days).
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Its axis is tilted by 26.73 degrees with respect to its orbit around the Sun, which is
similar to Earth's 23.5-degree tilt. This means that, like Earth, Saturn experiences
seasons.
Structure
Like Jupiter, Saturn is made mostly of hydrogen and helium. At Saturn's
center is a dense core of metals like iron and nickel surrounded by rocky material
and other compounds solidified by the intense pressure and heat. It is enveloped
by liquid metallic hydrogen inside a layer of liquid hydrogen—similar to Jupiter's core but
considerably smaller.
It's hard to imagine, but Saturn is the only planet in our solar system whose
average density is less than water. The giant gas planet could float in a bathtub if such a
colossal thing existed.
Formation
Saturn took shape when the rest of the solar system formed about 4.5 billion
years ago, when gravity pulled swirling gas and dust in to become this gas giant. About 4
billion years ago, Saturn settled into its current position in the outer solar system, where
it is the sixth planet from the Sun.
Surface
As a gas giant, Saturn doesn’t have a true surface. The planet is mostly swirling
gases and liquids deeper down. While a spacecraft would have nowhere to land on
Saturn, it wouldn’t be able to fly through unscathed either. The extreme pressures and
temperatures deep inside the planet crush, melt and vaporize spacecraft trying to fly into
the planet.
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Atmosphere
Saturn is blanketed with clouds that appear as faint stripes, jet streams and
storms. The planet is many different shades of yellow, brown and grey.
Winds in the upper atmosphere reach 1,600 feet per second (500 meters per
second) in the equatorial region. In contrast, the strongest hurricane-force winds on
Earth top out at about 360 feet per second (110 meters per second). And the pressure—
the same kind you feel when you dive deep underwater—is so powerful it squeezes gas
into liquid.
Saturn's north pole has an interesting atmospheric feature—a six-sided jet
stream. This hexagon-shaped pattern was first noticed in images from the Voyager I
spacecraft and has been more closely observed by the Cassini spacecraft since.
Spanning about 20,000 miles (30,000 kilometers) across, the hexagon is a wavy jet
stream of 200-mile-per-hour winds (about 322 kilometers per hour) with a massive,
rotating storm at the center. There is no weather feature like it anywhere else in the solar
system.
Magnetosphere
Saturn's magnetic field is smaller than Jupiter's but still 578 times as powerful as
Earth's. Saturn, the rings, and many of the satellites lie totally within Saturn's enormous
magnetosphere, the region of space in which the behavior of electrically charged
particles is influenced more by Saturn's magnetic field than by the solar wind.
Aurorae occur when charged particles spiral into a planet's atmosphere along
magnetic field lines. On Earth, these charged particles come from the solar wind. Cassini
showed that at least some of Saturn's aurorae are like Jupiter's and are largely
unaffected by the solar wind. Instead, these aurorae are caused by a combination of
particles ejected from Saturn's moons and Saturn's magnetic field's rapid rotation rate.
But these "non-solar-originating" aurorae are not completely understood yet.
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Rings
This Cassini image from 2012 shows Titan and its host planet Saturn. Image Credit: NASA/JPL-Caltech/SSI
Saturn's rings are thought to be pieces of comets, asteroids or shattered
moons that broke up before they reached the planet, torn apart by Saturn's
powerful gravity. They are made of billions of small chunks of ice and rock coated
with another material such as dust. The ring particles mostly range from tiny, dustsized icy grains to chunks as big as a house. A few particles are as large as mountains.
The rings would look mostly white if you looked at them from the cloud tops of Saturn,
and interestingly, each ring orbits at a different speed around the planet.
Saturn's ring system extends up to 175,000 miles (282,000 kilometers) from the
planet, yet the vertical height is typically about 30 feet (10 meters) in the main rings.
Named alphabetically in the order they were discovered, the rings are relatively close to
each other, with the exception of a gap measuring 2,920 miles (4,700 kilometers) wide
called the Cassini Division that separates Rings A and B. The main rings are A, B
and C. Rings D, E, F and G are fainter and more recently discovered.
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Moons
Saturn is home to a vast array of intriguing and unique worlds. From the hazeshrouded surface of Titan to crater-riddled Phoebe, each of Saturn's moons tells
another piece of the story surrounding the Saturn system. Currently Saturn has 53
confirmed moons with 29 additional provisional moons awaiting confirmation.
Potential for Life
Saturn's environment is not conducive to life as we know it. The temperatures,
pressures and materials that characterize this planet are most likely too extreme and
volatile for organisms to adapt to.
While planet Saturn is an unlikely place for living things to take hold, the same is
not true of some of its many moons. Satellites like Enceladus and Titan, home to internal
oceans, could possibly support life.
Source: https://solarsystem.nasa.gov/planets/saturn/in-depth/
Uranus
The Planet Uranus
Source: NASA/Space Telescope Science Institute
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Uranus is the seventh planet from the Sun with the third largest diameter in our
solar system; it is very cold and windy. The ice giant is surrounded by 13 faint rings and
27 small moons as it rotates at a nearly 90-degree angle from the plane of its orbit.
This unique tilt makes Uranus appear to spin on its side, orbiting the Sun like a
rolling ball.
The first planet found with the aid of a telescope, Uranus was discovered in 1781
by astronomer William Herschel, although he originally thought it was either a comet or
a star. It was two years later that the object was universally accepted as a new planet, in
part because of observations by astronomer Johann Elert Bode.
William Herschel tried unsuccessfully to name his discovery Georgium Sidus
after King George III. Instead the planet was named for Uranus, the Greek god of the
sky, as suggested by Johann Bode.
Size and Distance
With a radius of 15,759.2 miles (25,362 kilometers), Uranus is 4 times wider
than Earth. If Earth was the size of a nickel, Uranus would be about as big as a softball.
From an average distance of 1.8 billion miles (2.9 billion kilometers), Uranus is
19.8 astronomical units away from the Sun. One astronomical unit (abbreviated as
AU), is the distance from the Sun to Earth. From this distance, it takes sunlight 2 hours
and 40 minutes to travel from the Sun to Uranus.
Orbit and Rotation
One day on Uranus takes about 17 hours (the time it takes for Uranus to rotate or
spin once). And Uranus makes a complete orbit around the Sun (a year in Uranian time)
in about 84 Earth years (30,687 Earth days).
Uranus is the only planet whose equator is nearly at a right angle to its orbit, with
a tilt of 97.77 degrees—possibly the result of a collision with an Earth-sized object
long ago. This unique tilt causes the most extreme seasons in the solar system. For
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nearly a quarter of each Uranian year, the Sun shines directly over each pole, plunging
the other half of the planet into a 21-year-long, dark winter.
Uranus is also one of just two planets that rotate in the opposite direction
than most of the planets (Venus is the other one), from east to west.
Structure
Uranus is one of two ice giants in the outer solar system (the other is Neptune).
Most (80 percent or more) of the planet's mass is made up of a hot dense fluid of "icy"
materials—water, methane and ammonia—above a small rocky core. Near the core, it
heats up to 9,000 degrees Fahrenheit (4,982 degrees Celsius).
Uranus is slightly larger in diameter than its neighbor Neptune, yet smaller in
mass. It is the second least dense planet; Saturn is the least dense of all.
Uranus gets its blue-green color from methane gas in the atmosphere.
Sunlight passes through the atmosphere and is reflected back out by Uranus' cloud tops.
Methane gas absorbs the red portion of the light, resulting in a blue-green color.
Formation
Uranus took shape when the rest of the solar system formed about 4.5 billion
years ago, when gravity pulled swirling gas and dust in to become this ice giant. Like its
neighbor Neptune, Uranus likely formed closer to the Sun and moved to the outer solar
system about 4 billion years ago, where it is the seventh planet from the Sun.
Surface
As an ice giant, Uranus doesn‘t have a true surface. The planet is mostly swirling
fluids. While a spacecraft would have nowhere to land on Uranus, it wouldn‘t be able to
fly through its atmosphere unscathed either. The extreme pressures and temperatures
would destroy a metal spacecraft.
48
Atmosphere
Uranus' atmosphere is mostly hydrogen and helium, with a small amount of
methane and traces of water and ammonia. The methane gives Uranus its signature
blue color.
While Voyager 2 saw only a few discrete clouds, a Great Dark Spot and a small
dark spot during its flyby in 1986, more recent observations reveal that Uranus exhibits
dynamic clouds as it approaches equinox, including rapidly changing bright features.
Uranus' planetary atmosphere, with a minimum temperature of 49K (-224.2
degrees Celsius) makes it even colder than Neptune in some places.
Wind speeds can reach up to 560 miles per hour (900 kilometers per hour) on
Uranus. Winds are retrograde at the equator, blowing in the reverse direction of the
planet’s rotation. But closer to the poles, winds shift to a prograde direction, flowing with
Uranus' rotation.
Magnetosphere
Uranus has an unusual, irregularly shaped magnetosphere. Magnetic fields are
typically in alignment with a planet's rotation, but Uranus' magnetic field is tipped over:
the magnetic axis is tilted nearly 60 degrees from the planet's axis of rotation, and
is also offset from the center of the planet by one-third of the planet's radius.
Auroras on Uranus are not in line with the poles (like they are on Earth, Jupiter
and Saturn) due to the lopsided magnetic field.
The magnetosphere tail behind Uranus opposite the Sun extends into space for
millions of miles. Its magnetic field lines are twisted by Uranus’ sideways rotation into a
long corkscrew shape.
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Rings
Uranus has two sets of rings. The inner system of nine rings consists mostly of
narrow, dark grey rings. There are two outer rings: the innermost one is reddish like
dusty rings elsewhere in the solar system, and the outer ring is blue like Saturn's E ring.
In order of increasing distance from the planet, the rings are called Zeta, 6, 5, 4, Alpha,
Beta, Eta, Gamma, Delta, Lambda, Epsilon, Nu and Mu. Some of the larger rings are
surrounded by belts of fine dust.
Moons
Uranus has 27 known moons. While most of the satellites orbiting other planets
take their names from Greek or Roman mythology, Uranus' moons are unique in being
named for characters from the works of William Shakespeare and Alexander Pope.
All of Uranus' inner moons appear to be roughly half water ice and half rock. The
composition of the outer moons remains unknown, but they are likely captured asteroids.
Potential for Life
Uranus' environment is not conducive to life as we know it. The temperatures,
pressures and materials that characterize this planet are most likely too extreme and
volatile for organisms to adapt to.
Source: https://solarsystem.nasa.gov/planets/uranus/in-depth/
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Neptune
The Planet Neptune
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VFRUYHSggGBolHRUVITEhJSkrLi…
Dark, cold and whipped by supersonic winds, ice giant Neptune is the eighth and
most distant planet in our solar system. More than 30 times as far from the Sun as Earth,
Neptune is the only planet in our solar system not visible to the naked eye. In 2011
Neptune completed its first 165-year orbit since its discovery in 1846.
Neptune is so far from the Sun that high noon on the big blue planet would seem
like dim twilight to us. The warm light we see here on our home planet is roughly 900
times as bright as sunlight on Neptune.
The ice giant Neptune was the first planet located through mathematical
calculations. Using predictions made by Urbain Le Verrier, Johann Galle discovered
the planet in 1846. The planet is named after the Roman god of the sea, as suggested
by Le Verrier
Size and Distance
With a radius of 15,299.4 miles (24,622 kilometers), Neptune is about four times wider
than Earth. If Earth were the size of a nickel, Neptune would be about as big as a
baseball.
From an average distance of 2.8 billion miles (4.5 billion kilometers), Neptune is
30 astronomical units away from the Sun. One astronomical unit (abbreviated as AU),
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is the distance from the Sun to Earth. From this distance, it takes sunlight 4 hours to
travel from the Sun to Neptune.
Orbit and Rotation
One day on Neptune takes about 16 hours (the time it takes for Neptune to
rotate or spin once). And Neptune makes a complete orbit around the Sun (a year in
Neptunian time) in about 165 Earth years (60,190 Earth days).
Sometimes Neptune is even farther from the Sun than dwarf planet Pluto. Pluto's
highly eccentric, oval-shaped orbit brings it inside Neptune's orbit for a 20-year period
every 248 Earth years. This switch, in which Pluto is closer to the Sun than Neptune,
happened most recently from 1979 to 1999. Pluto can never crash into Neptune, though,
because for every three laps Neptune takes around the Sun, Pluto makes two. This
repeating pattern prevents close approaches of the two bodies.
Neptune‘s axis of rotation is tilted 28 degrees with respect to the plane of its orbit
around the Sun, which is similar to the axial tilts of Mars and Earth. This means that
Neptune experiences seasons just like we do on Earth; however, since its year is so
long, each of the four seasons lasts for over 40 years.
Structure
Neptune is one of two ice giants in the outer solar system (the other is Uranus).
Most (80 percent or more) of the planet's mass is made up of a hot dense fluid of
"icy" materials—water, methane and ammonia—above a small, rocky core. Of the
giant planets, Neptune is the densest.
Scientists think there might be an ocean of super-hot water under Neptune's cold
clouds. It does not boil away because incredibly high pressure keeps it locked inside.
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Formation
Neptune took shape when the rest of the solar system formed about 4.5 billion
years ago, when gravity pulled swirling gas and dust in to become this ice giant. Like its
neighbor Uranus, Neptune likely formed closer to the Sun and moved to the outer solar
system about 4 billion years ago.
Surface
Neptune does not have a solid surface. Its atmosphere (made up mostly of
hydrogen, helium and methane) extends to great depths, gradually merging into water
and other melted ices over a heavier, solid core with about the same mass as Earth.
Atmosphere
Neptune's atmosphere is made up mostly of hydrogen and helium with just a
little bit of methane. Neptune's neighbor Uranus is a blue-green color due to such
atmospheric methane, but Neptune is a more vivid, brighter blue, so there must be an
unknown component that causes the more intense color.
Neptune is our solar system's windiest world. Despite its great distance and
low energy input from the Sun, Neptune's winds can be three times stronger than
Jupiter's and nine times stronger than Earth's. These winds whip clouds of frozen
methane across the planet at speeds of more than 1,200 miles per hour (2,000
kilometers per hour). Even Earth's most powerful winds hit only about 250 miles per hour
(400 kilometers per hour).
In 1989 a large, oval-shaped storm in Neptune's southern hemisphere dubbed the
"Great Dark Spot" was large enough to contain the entire Earth. That storm has since
disappeared, but new ones have appeared on different parts of the planet.
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Magnetosphere
The main axis of Neptune's magnetic field is tipped over by about 47 degrees
compared with the planet's rotation axis. Like Uranus, whose magnetic axis is tilted
about 60 degrees from the axis of rotation, Neptune's magnetosphere undergoes wild
variations during each rotation because of this misalignment. The magnetic field of
Neptune is about 27 times more powerful than that of Earth.
Rings
This Voyager 2 image, taken in 1989, was the first to show Neptune's rings in detail. Credit: NASA/JPL
Neptune at least five main rings and four prominient ring arcs that we know of so
far. Starting near the planet and moving outward, the main rings are named Galle,
Leverrier, Lassell, Arago and Adams. The rings are thought to be relatively young and
short-lived.
Neptune's ring system also has peculiar clumps of dust called arcs. Four
prominent arcs named Liberté (Liberty), Egalité (Equality), Fraternité (Fraternity)
and Courage are in the outermost ring, Adams. The arcs are strange because the
laws of motion would predict that they would spread out evenly rather than stay clumped
together. Scientists now think the gravitational effects of Galatea, a moon just inward
from the ring, stabilizes these arcs.
54
Moons
Neptune has 14 known moons. Neptune's largest moon Triton was discovered
on October 10, 1846, by William Lassell, just 17 days after Johann Gottfried Galle
discovered the planet. Since Neptune was named for the Roman god of the sea, its
moons are named for various lesser sea gods and nymphs in Greek mythology.
Triton is the only large moon in the solar system that circles its planet in a
direction opposite to the planet's rotation (a retrograde orbit), which suggests that
it may once have been an independent object that Neptune captured. Triton is
extremely cold, with surface temperatures around minus 391 degrees Fahrenheit (minus
235 degrees Celsius). And yet, despite this deep freeze at Triton, Voyager 2 discovered
geysers spewing icy material upward more than 5 miles (8 kilometers). Triton's thin
atmosphere, also discovered by Voyager, has been detected from Earth several times
since, and is growing warmer, but scientists do not yet know why.
Potential for Life
Neptune's environment is not conducive to life as we know it. The temperatures,
pressures and materials that characterize this planet are most likely too extreme and
volatile for organisms to adapt to.
Source:https://solarsystem.nasa.gov/planets/neptune/in-depth/
The Dwarf Planets
With the present classification, there are now eight planets in our solar system,
along with a new classification of objects called Dwarf Planets . Currently there are
three Dwarf Planets: Pluto, Ceres (previously classified as an asteroid), and Eris. A
subclass of Dwarf planets is called the Plutoids ; these ice dwarfs are trans-Neptunian
(past the planet Neptune) planets that orbit the Sun and are large enough to be
somewhat spherical in shape. It‘s important to note that these rulings only apply to
our solar system, not to other stellar systems with planets .
Source: https://courses.lumenlearning.com/atd-fscj-introastronomy/chapter/what-is-a-planet/
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The Earth-Moon System
The Earth‘s Moon
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQ1EMKnhGniC8oGjTByDULnmGSod0NQDoOvow&usqp=CAU
Facts About The Moon

The Moon is Earth’s only natural satellite and the fifth largest moon in the solar
system.

The Moon’s presence helps stabilize our planet’s wobble and moderate our climate.

The Moon’s distance from Earth is about 240,000 miles (385,000km).

The Moon has a very thin atmosphere called an exosphere.

The Moon’s entire surface is cratered and pitted from impacts.
The brightest and largest object in our night sky, the Moon makes Earth a more
livable planet by moderating our home planet's wobble on its axis, leading to a relatively
stable climate. It also causes tides, creating a rhythm that has guided humans for
thousands of years.
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The Moon was likely formed after a Mars-sized body collided with Earth several
billion years ago. Earth's Moon is the only place beyond Earth where humans have set
foot, so far.
Earth's only natural satellite is simply called "the Moon" because people didn't
know other moons existed until Galileo Galilei discovered four moons orbiting Jupiter in
1610.
In Latin, the Moon is called Luna, which is the main adjective for all things Moonrelated: lunar.
Size and Distance
With a radius of about 1,080 miles (1,740 kilometers), the Moon is less than a
third of the width of Earth. If Earth were the size of a nickel, the Moon would be about as
big as a coffee bean.
The Moon is an average of 238,855 miles (384,400 kilometers) away. That
means 30 Earth-sized planets could fit in between Earth and the Moon.
The Moon is slowly moving away from Earth, getting about an inch farther away
each year.
In October 2020, NASA‘s Stratospheric Observatory for Infrared Astronomy
(SOFIA) confirmed, for the first time, water on the sunlit surface of the Moon. This
discovery indicates that water may be distributed across the lunar surface, and not
limited to cold, shadowed places. SOFIA detected water molecules (H2O) in Clavius
Crater, one of the largest craters visible from Earth, located in the Moon‘s southern
hemisphere.
Atmosphere
The Moon has a very thin and weak atmosphere, called an exosphere. It does not
provide any protection from the Sun's radiation or impacts from meteoroids.
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Magnetosphere
The early Moon may have developed an internal dynamo, the mechanism for
generating global magnetic fields for terrestrial planets, but today, the Moon has a very
weak magnetic field. The magnetic field here on Earth is many thousands of times
stronger than the Moon's magnetic field.
Rings
The Moon has no rings.
Moons
Earth's Moon has no moons of its own.
Potential for Life
The many missions that have explored the Moon have found no evidence to
suggest it has its own living things. However, the Moon could be the site of future
colonization by humans. The discovery that the Moon harbors water ice, and that the
highest concentrations occur within darkened craters at the poles, makes the Moon a
little more hospitable for future human colonists.
Source: https://solarsystem.nasa.gov/moons/earths-moon/in-depth/
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Phases of the Moon
Credit: NASA/Bill Dunford
https://solarsystem.nasa.gov/internal_resources/3969
Our Moon doesn't shine, it reflects. Just like daytime here on Earth, sunlight
illuminates the Moon. When sunlight hits off the Moon's far side — the side we can't see
is called a new Moon.
When sunlight reflects off the near side, we call it a full Moon.
The rest of the month we see parts of the daytime side of the Moon, or phases.
These eight phases are, in order, new Moon, waxing crescent, first quarter, waxing
gibbous, full Moon, waning gibbous, third quarter and waning crescent. The cycle
repeats once a month (every 29.5 days).
Sidereal vs. Synodic Month

The Moon completes an orbit around the Earth once every 27.3 days.
o
This time period is called the ``Sidereal'' lunar month. It is the "true" orbital
period of the Moon about the Earth.
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
The time interval between New Moons is 29.5 days?
o
A New Moon occurs when the Moon lies between the Sun and the Earth.
o
As a lunar month progresses the Earth moves along its own orbit around
the Sun.
Sidereal vs. Synodic Months
https://faculty.virginia.edu/skrutskie/images/sidsyn.gif
o
After 27.3 days (i.e. a sidereal month) the Earth has moved to a new
position in its orbit. The Moon must travel along its orbit for an
additional 2.2 days in order to re-align with the Sun and thus become
``New'' again.
o
This time interval between New Moons is called the ``Synodic'' lunar month
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What is a Lunar Eclipse?
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G4euKAjPFoPACAkRm0bQmwANlP///8kRWsgRGwMh3YQRmv5ulcUP2vNbJXYcp
During a lunar eclipse, Earth comes between the Sun and the Moon, blocking the
sunlight falling on the Moon.
There are two kinds of lunar eclipses:
1.
A total lunar eclipse occurs when the Moon and Sun are on opposite sides of
Earth.
2.
A partial lunar eclipse happens when only part of Earth's shadow covers the
Moon.
During some stages of a lunar eclipse, the Moon can appear reddish. This is
because the only remaining sunlight reaching the Moon at that point is from around the
edges of the Earth, as seen from the Moon's surface. From there, an observer during an
eclipse would see all Earth's sunrises and sunsets at once.
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Understanding Lunar Eclipses
A lunar eclipse occurs when the Moon passes through the Earth's shadow, just as
a solar eclipse occurs when part of the Earth passes through the Moon's shadow.
So why don't eclipses happen twice a month?
The reason is that the Moon's orbit around the Earth is tilted relative to the Earth's orbit
around the Sun.
Source:https://solarsystem.nasa.gov/moons/earths-moon/lunar-phases-andeclipses/#:~:text=The%20rest%20of%20the%20month,month%20(every%2029.5
%20days).
Effects of the Moon to Earth
Tides
Tides are caused by gravitational pull of the moon and the sun.
Tides are also the regular rise and fall of the ocean‘s waters. Along coasts, the
water slowly rises up over the shore and then slowly falls back again. When the water
has risen to its highest level, covering much of the shore, it is at high tide. When the
water falls to its lowest level, it is at low tide.
Causes
Forces
of
that
Earth’s rotation is
contribute
a
tidal
to
Tides
tides
are
called tidal
constituent.
The
major
constituents.
tidal
constituent
The
is
the moon’s gravitational pull on the Earth. The closer objects are, the greater the
gravitational force is between them. Although the sun and moon both exert gravitational
force on the Earth, the moon‘s pull is stronger because the moon is much closer to the
Earth than the sun is.
Source: https://www.nationalgeographic.org/article/cause-effect-tides/
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Types of Tides
Tides Based on Frequency
Semi-Diurnal
Tides
Diurnal Tides
Mixed
Tides Based on the Position of Earth, Sun,
Spring Tides
and the Moon
Neap Tides
https://cdn1.byjus.com/wp-content/uploads/2020/08/Types-of-Tides-.png
63
Semi-Diurnal Tides
A semi-diurnal tidal cycle is the one with two nearly equal high tides and two
low tides each day. The interval between the high and the low tides is of around 12
hours and 25 minutes. Semi-Diurnal tides are most widespread in the Indian Ocean,
Eastern African Coast, and Bay of Bengal
Diurnal Tides
It means four tides in a day. Two tides by the sun and two by the moon.
Spring Tide is an exceptionally high tide generated by the complementary factor played
by the Sun with respect to the moon. It should be noted that when Sun, Moon, and Earth
are in the same line, the position is known as the Syzygy. This syzygy can be of 2 types
1. Conjunction: when the moon and sun are on the same side
2. Opposition: When the moon and sun are on the opposite side In both of these
conditions, the magnitude of the tide will be equally high.
Mixed Tides
A tidal cycle with two unequal high and low tides lead to the formation of the
mixed tidal cycle, or simply called mixed tide. This tidal cycle has both semi-diurnal and
diurnal oscillations. It is widely observed in the Gulf of Mexico and the Caribbean Sea.
Southeastern Brazilian coast also witnesses mixed tides.
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https://cdn1.byjus.com/wp-content/uploads/2020/08/Spring-Neap-Tides.png
Spring Tides
Spring tides are formed when the sun and the moon are in line with each
other and pull the ocean surface in the same direction. This leads to higher high
tides and lowers low tides. In a lunar month, it occurs twice. It is also known by the name
of ‗King Tide.‘
These occur in full or new moon days. In both new moon or full moon days, the
sun‘s gravitational pull is added to the moon‘s gravitational pull on Earth, causing the
oceans to bulge a bit more than usual. This results in ‗higher‘ high tides and ‗lower‘ low
tides.
Neap Tides
It occurs seven days after the spring tide. The prominent point is that the sun
and the moon are at the right angle to each other. This tide occurs during the first and
the last quarter of the moon. The gravitational pull of the moon and the resulting oceanic
bulge is cancelled out by the gravitational pull of the sun and its resulting oceanic bulge.
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Also, in contrast to spring tides, the high tides are ‗lower‘ and the low tides are
comparatively ‗higher‘ in neap tides.
How do tides work?
The mechanism of tides could be understood by understanding the gravitational
force of the Sun and the Moon. These bodies experience the gravitational pull over each
other depending upon their mass and the distance between them. Since the Sun is far
away from the Earth as compared to the Moon. Hence, the Sun’s gravitational pull
is lesser over the Earth than the moon. Thus, the moon determines the magnitude
of the tide. It is supposed that only the water bodies are pulled by the gravitational pull,
however, it is not the fact. It is both the land and water bodies that get pulled by the
gravitation. Since the relative pull of the land is less in comparison to that of water, the
effect of gravitation on the water bodies is more. It should be noted that the magnitude of
a tide is determined by the relative position of the Moon, the Sun, and the Earth.
Impact of Tides
1. Tides raise the level of seawater and hence exposes a large part of the ocean for
erosion
2. It is helpful for the tidal ports that have shallow water which is a constraint for the
big ships to enter.
3. Tidal currents are a very potential source of tidal energy which is harnessed by
many developed countries on a very large scale and to some extent in India as
well.
4. It can be devastating in cases where the tide gets too huge and results in the
flooding of the nearby coastal regions.
5. Tides are very helpful for ecosystems such as the mangrove forests and coral
reefs to grow and sustain.
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Characteristics of Tides
Tide changes as per the 4 stages given below.
1. Flood Tide – Over a period of several hours there will be a rise in sea level.
2. High Tide – This is a stage where the water reaches its maximum level.
3. Ebb Tide – This is a stage where sea level keeps receding over several hours.
4. Low Tide – The Level of Seawater stops receding.
Guide Questions
1. What is astronomy? How can it be helpful to human beings?
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2. Among the topics presented, which is the one you appreciate the most?
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3. What is the insight that you gained from this module?
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Learning Activity
Divide the class into 5 groups, and then ask them to create a semantic
web/concept map/simulation of their assigned topic. Presentation of output will be based
on the following criteria:
Rubric in Grading:
Criterion
Exemplary
Comments
Performance
Relevance to the The work reflects a
Theme (3 points)
clear and precise
message
consistent with the
topics presented.
Visual
The
work
Impact/Appeal
visually
(3 points)
aesthetically
is
and
appealing.
Creativity (2pts)
Neatness and
Clarity (2pts)
The work was
artistically
executed depicting
unique ideas and
insights about the
topic.
The work is well; in
order, neat and
clean.
Total Points
68
Points
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