Year 9 Astronomy – Beyond our Solar System – Summary Notes
Name: ___________________________
1. Some terminology in Astronomy:
a. Astronomy = the branch of physics that studies celestial bodies and the universe as
a whole; the study of everything that is or was in space beyond the Earth's
atmosphere. The scientific study of the Universe and what it contains (planets,
stars, galaxies, etc), and how these things formed and evolved over time.
b. Celestial bodies = they include all stars, planets, asteroids, planets and natural
satellites (moon), comets, and galaxies.
c. Cosmology & astrophysics are sub-fields of astronomy, focusing on the properties
of the universe as a whole (cosmology) and the physical or chemical properties of
celestial bodies (astrophysics).
d. Cosmologist - an astronomer who studies the evolution and space-time relations of
the universe.
e. Astronomer - a physicist who studies astronomy; a scientist who observes and
studies planets, stars, and galaxies.
f. Astrology = the study of the movements and relative positions of celestial bodies
and their supposed influence on human affairs.
g. NASA = National Aeronautics and Space Administration: an independent agency of
the United States government responsible for aviation
and spaceflight.
NASA was established in 1958, which conducts
research on problems of flight on Earth and in space.
NASA creates and operates aviation and space
vehicles, and performs test flights and missions,
coordinates programs for the peaceful exploration of
space and arranges cooperative programs involving
the United States and other nations to develop
scientific and engineering resources for peaceful
purposes.
2. Big Bang Theory:
a. Most astronomers believe the Universe began in a Big Bang about 14 billion years
ago.
b. At that time, the entire Universe was inside a bubble that was thousands of times
smaller than a pinhead. It was hotter and denser than anything we can imagine.
c. Then it suddenly exploded. The Universe that we know was born. Time, space and
matter all began with the Big Bang.
d. In a fraction of a second, the Universe grew from smaller than a single atom to
bigger than a galaxy. And it kept on growing at a fantastic rate. It is still expanding
today.
e. Over the next three minutes, the temperature dropped below 1 billion degrees
Celsius. It was now cool enough for the protons and neutrons to come together,
forming hydrogen and helium nuclei.
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After 300 000 years, the Universe had cooled to about 3000 degrees. Atomic nuclei
could finally capture electrons to form atoms. The Universe filled with clouds of
hydrogen and helium gas.
3. Information about our Solar system:
a. A Solar system = A system of planets, moons, asteroids, comets, dust, gas, and any
other objects that orbit a star, tied to it by the star’s gravitational force.
b. Our Solar System consists of the Sun and those celestial objects bound to it by
gravity.
c. These objects are the eight planets, their 166 known moons,[1] five dwarf planets,
and billions of small bodies.
d. The small bodies include asteroids, icy Kuiper belt objects, comets, meteoroids, and
interplanetary dust.
e. The 4 planets orbiting closer to the Sun are the rocky planets as they all consists of
a rocky surface and a rocky core even they are molten rocks in their cores:
Mercury ---Venus -- Earth -- Mars
f. The further 4 planets are known as “ Gas Giants” as they are much larger than the
Earth and they consist mainly of gases. They may have molten rocky cores at an
extreme high temperature –more than 10,000 0C.
Jupiter – Saturn -- Uranus – Neptune
g. Special features of each planet:
Planet
Special Features
Mercury
 Smallest planet and closest to the Sun
 Lack of Atmosphere, having numerous craters on the surface
as a result of impacts from asteroids
 Biggest extremes of temperature among all planets.
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Symbol
Venus
Earth
 Almost the same size as the Earth but the atmosphere
consists of corrosive sulphuric acid
 Venus rotates from East to West, which is just the opposite
of Earth and most of the other planets.
 A day is long than a year on Venus
 Hottest planet (4830C) because the heat is trapped by the
high level atmospheric carbon dioxide.
 Earth is the only planet which supports animal and plant life.
 The only planet with oceans of warm water.
Mars
 Red planet; many similarities to the Earth
 During the Martian winter, the planet has ice caps at the
north and south poles like Earth does, but these caps are
made of frozen carbon dioxide, or "dry ice".
 The largest volcano in the Solar System is on Mars.
Jupiter
 The largest planet; having the highest gravity
 All gases – mainly hydrogen and helium (no surface for
spacecraft to land on)
 Great Red Spot – about 20,000 km in diameter - a huge, high
storm that has been swirling around Jupiter for hundreds of
years. (it was 40,000 km in diameter a century ago)
 Have greatest number of moons 63 – the largest moon is
bigger than Mercury and almost the same size as Mars
 The large beautiful ring of about 260000 km in diameter,
other gas planets have faint rings .
Saturn
Uranus
 "laying on its side" as it faces the Sun. Earth faces the sun
standing almost straight up, with the north and south poles
at the top and bottom. Uranus, however, has its south pole is
facing the Sun.
 It rotates, or spins, from east to west which is the exact
opposite of the way that Earth spins.
 Its north pole stays dark for 42 years at a time.
Neptune
 Neptune's blue color is caused by the methane (CH4) in its
atmosphere; this molecule absorbs red light.
 Great Dark Spot in the southern hemisphere – about the
same diameter as the Earth.
 Neptune can have winds up to 3800 km per second.
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4. Pluto – Not one of us!!
a. Pluto was discovered and known as the last planet of our solar system since 1930.
b. In 2006 it was re-classified as a “Dwarf Planet”.
c. Due to this in 2006, the IAU (International Astronomical Union) got together and
defined specifically what a 'Planet' is:
 The object must be in orbit around the Sun.
 The object must be massive enough to be a sphere by its own gravitational
force.
 It must have cleared the neighbourhood around its orbit.
d. Pluto fails to meet the third condition, since its mass was only 0.07 times that of the
mass of the other objects in its orbit. (Earth's mass, by contrast, is 1.7 million times
the remaining mass in its own orbit).
e. The IAU further resolved that Pluto be classified in the simultaneously created
dwarf planet category.
f. A dwarf planet = a celestial body that orbits the sun and is large enough to assume
a nearly round shape, but that does not clear the neighborhood around its orbit and
is not a satellite of a planet.
g. Pluto is situated in a space
beyond the Neptune orbit,
known as the “Kuiper Belt”.
h. Kuiper Belt – discovered in
1992. It is similar to the
Asteroid Belt between the
orbits of Mars and Jupiter.
Kulper Belt is much wider,
containing at least 3 dwarf
planets (including Pluto) and
other Kulper Belt Objects
(KBOs).
i. But while the asteroid belt is
composed primarily of rock and
metal, the Kuiper belt objects
are composed largely of frozen
volatiles such as methane,
ammonia and water.
j. Pluto has a very eccentric orbit;
that means that its distance from the sun varies a
lot during its orbit around the sun. Sometimes it is
even closer to the Sun than the planet Neptune (it
was that way from January 1979 to February 11,
1999)! Pluto also rotates about its axis in the
opposite direction from most of the other planets.
k. In 2015, a spacecraft called New Horizons
(launched by NASA in 2006) will visit Pluto.
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5. Some other common space objects in our Solar System:
Space object
What are they?
Moon
any natural satellite of a planet, a celestial object that is revolving around a
planet. There are 169 moons in our Solar system as of 2006.
Comet
a relatively small celestial body consisting of a frozen mass that travels
around the sun in a highly elliptical orbit, it exhibits a visible coma
(atmosphere) or a tail.
Asteroid
any of numerous small celestial bodies composed of rock and metal that
move around the sun (mainly between the orbits of Mars and Jupiter); it is
irregular in shape. (50 – 1000 km in length)
Meteoroid
A solid rock fragment moving in interplanetary space, of a size
considerably smaller than a asteroid.
Meteor
The visible path of a meteoroid that enters Earth's atmosphere, commonly
called a "shooting star" or "falling star".
Meteorite
A stony or metallic object that is the remains of a meteoroid that has
reached the earth's surface.
6.
Asteroid Ida 55 km
The largest Meteorite –
50 tonnes; 9 m3; hit the earth
80,000 years ago.
Comet with a glowing tail
A Meteorite
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6. Summary of the History of Space Exploration:
Year
Event
1957
the Soviets launched the first artificial satellite, Sputnik 1, into space.
1958
The first U.S. satellite, Explorer 1, went into orbit
1959
The first successful space probe was the Soviet Luna 1 flyby of the Moon
1961
First man (a Russian) to orbit the Earth in Vostok 1
1958
The first U.S. satellite, Explorer 1, went into orbit
1967
Mariner V landed on Venus
1969
Astronaut Neil Armstrong took “a giant step for mankind” as he stepped onto
the moon – Apollo 11 mission.
1971
The first successful objects to land on the surface of Mars were two Soviet
probes, Mars 2 and Mars 3 from the Mars probe program, launched in 1971,
but both lost contact within seconds of landing.
1975
Mariner 10 probe, which flew past the rocky world three times
1977
The Launch of Voyager 1 - an 733-kilogram probe; Voyager 1 had as its
primary targets the planets Jupiter and Saturn and their associated moons
and rings; its current mission is the detection of the heliopause and particle
measurements of solar wind and the interstellar medium. Voyager 1 is the
farthest human-made object from Earth
1970s
Skylab, America’s first space station;
the world’s first internationally crewed (American and Russian) space
mission.
1981
the launch of the space shuttle Columbia ushered in a period of reliance on
the reusable shuttle for most civilian and military space missions.
1986
the shuttle Challenger exploded after launch, killing its crew of seven.
1990
Hubble Space Telescope was completed in 1985. The launch of Hubble was
delayed due to the 1986 Space Shuttle Challenger disaster. Hubble was
launched on the space shuttle on April 25, 1990.
1997
Cassini-Huygens mission - the launch of a sophisticated robotic spacecraft
equipped with 12 scientific experiments to orbit Saturn for a four-year period
and study the Saturnian system in detail. It took 6 years to reach Saturn in
2004.
1998-2008
The International Space Station (ISS) is now in orbit and permanently
crewed. In the decade since, 44 manned flights and 34 unmanned flights have
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carried further modules, solar arrays, support equipment, supplies and a total
of 167 human beings from 15 countries to the ISS, and it still has a ways to go
until it is done. Originally planned to be complete in 2003, the target date for
completion is now 2011.
2001
The first Space Tourist was Dennis Tito.
2003
NASA launched a robotic probe to Mars.
2003
Galileo plunged into Jupiter's crushing atmosphere. Galileo was the first to
measure Jupiter's atmosphere with a descent probe and the first to conduct
long-term observations of the Jovian system from orbit. It was also the only
direct observations of a comet colliding with a planet.
2003
China sent first man to Space successfully.
2004
The Crew Exploration Vehicle (or CEV) was the conceptual component of the
Vision for Space Exploration that later became known as the Orion spacecraft.
The concept for the vehicle was officially announced in a speech given by
George W. Bush at NASA Headquarters on January 14, 2004.
2004
NASA’s Rovers – the Opportunity and the Spirit Rovers were successfully
landed on Mars surface and explore the surface for a lengthy period of time –
few years. They are looking for water and life on Mars.
2005
Huygens probe separated from the Cassini orbiter on December 25, 2004,
and landed on Titan (one of the Saturn’s moons) on January 14, 2005. It
returned 350 pictures from the surface.
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Tools and Equipment used for space exploration:
a. From Robots to Spaceships, many devices and equipment are required and yet to
invented for space exploration.
b. Space Stations provide a working platform in Earth orbit. The former USSR
launched the first space station, Salyut 1 in 1971. Skylab, America's first space
station launched 2 years later in 1973. Currently, the International Space Station is
a joint effort between many nations.
c. The space shuttle system is made up of three main components: The two Solid
Rocket Boosters (SRBs), which provide 80 percent of launch thrust; >The huge
rust-colored External Tank (ET), which feeds fuel to three Space Shuttle Main
Engines (SSMEs) during launch; The orbiter itself, which serves as the crew's home
in space and is equipped to dock with the International Space Station.
d. Space Shuttles can take off and land again to be used in the future.
e. Ever since Alan Shepard's history making flight in 1961, NASA astronauts have
relied on spacesuits to help them work and keep them safe. The suits have served
as personal spacecraft, protecting explorers during launch and entry, while
working on the International Space Station, or walking on the moon.
7. What is a Space Probe?
a. a rocket-propelled guided unmanned space vehicle designed to voyage beyond
Earth orbit. It is used to make observations and send back information to Earth
regarding these observed objects.
b. A space probe destined for a planet or other celestial body can be classified as a
"flyby", an "impactor", an "orbiter" or a "lander" mission.
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c. Probes can be named according to where to intend to go: planetary probes, lunar
probes, solar probes and probes to asteroids and comets. Probes can go to the
interplanetary (within our Solar system) or interstellar space (all the space within
a galaxy not occupied by stars or their planetary systems).
d. Upon landing some landers have released "rovers" which travel across the surface
of the celestral body upon which they have landed.
e. Some rovers have been designed to transport members of a human spaceflight
crew; others have been partially or fully autonomous robots.
Mars Rovers
Moon Rover – Apollo 15 mission
Mars Pathfinder 1997
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New Rovers by China
8. Artificial Satellites:
a. a manufactured object that continuously orbits Earth or some other body in space.
Most artificial satellites orbit Earth.
b. People use them to study the universe, help forecast the weather, transfer
telephone calls over the oceans, assist in the navigation of ships and aircraft,
monitor crops and other resources, and support military activities.
c. Artificial satellites also have orbited the moon, the sun, asteroids, and the planets
Venus, Mars, and Jupiter. Such satellites mainly gather information about the
bodies they orbit.
d. Piloted spacecraft in orbit, such as space capsules, space shuttle orbiters, and space
stations, are also considered artificial satellites.
e. So, too, are orbiting pieces of "space junk," such as burned-out rocket boosters and
empty fuel tanks that have not fallen to Earth.
f. Today, about 3,000 useful satellites and 6,000 pieces of space junk are orbiting
Earth.
g. Artificial satellites are classified according to their mission. There are six main
types of artificial satellites: (1) scientific research, (2) weather, (3)
communications, (4) navigation, (5) Earth observing, and (6) military.
h. A satellite remains in orbit because of a balance between the satellite's velocity
(speed at which it would travel in a straight line) and the gravitational force
between the satellite and Earth.
i. A high altitude, geosynchronous orbit lies above the equator at an altitude of about
35,900 kilometers. A satellite in this orbit travels around Earth's axis in exactly the
same time, and in the same direction, as Earth rotates about its axis. Thus, as seen
from Earth, the satellite always appears at the same place in the sky overhead.
9. What is GPS? Global Position System:
a. A system based on satellites that allows a user with a receiver to determine precise
coordinates for their location on the earth's surface.
b. The Global Positioning System (GPS) is a U.S. space-based radionavigation system
that provides reliable positioning, navigation, and timing services to civilian users
on a continuous worldwide basis -- freely available to all.
c. A civilian under international humanitarian law is a person who is not a member of
his or her country's armed forces.
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d. For anyone with a GPS receiver, the system will provide location and time. GPS
provides accurate location and time information for an unlimited number of people
in all weather, day and night, anywhere in the world.
e. The GPS is made up of three parts: satellites orbiting the Earth; control and
monitoring stations on Earth; and the GPS receivers owned by users.
f. Equipped with these GPS receivers, users can accurately locate where they are and
easily navigate to where they want to go, whether walking, driving, flying, or
boating.
g. GPS has many applications/uses: transportation systems worldwide, providing
navigation for aviation, ground, and maritime operations, disaster relief and
emergency services, banking, mobile phone operations. Farmers, surveyors,
geologists and countless others perform their work more efficiently, safely,
economically, and accurately using the free and open GPS signals.
h. The Global Positioning System (GPS) is actually a constellation of 27 Earth-orbiting
satellites (24 in operation and three extras in case one fails).
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10. What is a Light Year?
a. 1 light year = 9.4605284 × 1015 meters (a unit of very long distance)
b. the distance that light travels in a vacuum in 1 year; 9.46 trillion kilometers or
9,460,000,000,000 km
c. Basic formula on Speed = Distance / Time
Distance = Speed x Time
d. Speed of light = 299 792 458 m/s roughly equals to 300,000 km/s
Time in one year = 365 x 24 x 3600 seconds = 31536000 s
Distance = 300,000 x 31,536,000 = 9,460,800,000,000 km (same as above)
e. In our solar system, we tend to describe distances in terms of the Astronomical
Unit (AU). The AU is defined as the average distance between the Earth and the
Sun. It is approximately 150 million km Mercury can be said to be about 1/3 of an
AU from the Sun and Pluto averages about 40 AU from the Sun. The AU, however, is
not big enough of a unit when we start talking about distances to objects outside
our solar system.
f. Some distances in space:
i. The nearest star from Earth (Proxima
Centauri) is 4.24 light-years away.
ii. The Crab supernova is about 4,000 lightyears away.
iii. The Milky Way Galaxy is about 150,000
light-years across.
iv. The Andromeda Galaxy is 2.3 million lightyears away.
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11. What is a Star in the Universe?
a. a celestial body of hot gases that radiates energy derived from thermonuclear
reactions in the interior. It is held together as a spherical body by its own gravity.
b. Our Sun is one of the trillion stars in the universe.
c. Astronomers estimate there are about 100 thousand million stars in the Milky Way
alone. Outside that, there are millions upon millions of other galaxies also!
d. There are something like 1011 to 1012 stars in our galaxy, and there are perhaps
something like 1011 or 1012 galaxies.
e. With this simple calculation you get something like 1022 to 1024 stars in the
Universe.
12. Stars are classified by their spectra (the elements that they absorb) and their temperature.
There are seven main types of stars. In order of decreasing temperature, O, B, A, F, G, K,
and M. An easy mnemonic for remembering these is: "Oh be a fine girl, kiss me."
Temperature: Celsius = Kelvin + 273.
0° C = -273° Kelvin
13. What is a Constellation?
a. A group of stars that make a shape, often named
after mythological characters, people, animals, and
things.
b. The 88 official constellations defined by the
International Astronomical Union IAU are mostly
based upon those of the ancient Greek tradition,
passed down through the Middle Ages, which
includes the 'signs of the zodiac,' twelve
constellations through which the sun passes and
which thus have had special cultural significance.
c. Crux, the Southern Cross, is one of the easiest
constellations to spot in Southern Hemisphere
skies. It consists of four relatively bright stars in
close quarters.
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14. Overview of Galaxies:
a. As mentioned before, there are something like 1011 to 1012 stars in our galaxy, and
there are perhaps something like 1011 or
1012 galaxies.
b. Our solar system belongs to the Milky
Way Galaxy. There are around 400
billion to 3 trillion stars.
c. It belongs to one of the 3 main types of
Galaxies based on the shapes:
i. Spiral –flat disk with a central
bulge and spiral arms around eg.
Milky Way
ii. Elliptical - basically all bulge with
no disk. They can range from
spherical to elongated, footballlike shapes. Eg. Andromeda Galaxy. (2.5 million light years away from us)
iii. Irregular – no definite shape
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30 light year
thick
15. Formation of a New Star in the Universe:
a. all stars are formed from nebulae (the plural of nebula).
b. Nebula is a term for a cloud of gas, and stars form from gas.
c. A giant molecular cloud of gas may collapse and breaks up into separate pieces.
d. The matter starts to concentrate and increase in mass and gravity.
e. Heat starts to produce and can be detected as infra-red (heat) radiation.
f. Eventually, these pieces condense under the heat and pressure into gaseous
spheres called protostars.
g. Nuclear fusion produces helium and energy from fusing hydrogen nuclei. A new
star is formed.
h. The "burning" of Hydrogen stops the gas cloud from shrinking. At this point, the gas
cloud becomes a star. This is the present state of our Sun.
16. Fate of a star:
a. A star's life span and eventual fate are determined by the original mass of the star.
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b. After billions of years, most of the Hydrogen fuel has been "burned", and the star
begins to shrink again. The star has to turn to another source of fuel, Helium.
c. Very large, massive stars burn their fuel much faster than smaller stars. Their main
sequence may last only a few hundred thousand years.
d. Smaller stars will live on for billions of years because they burn their fuel much
more slowly. Our Sun is a medium size star.
e. When the smaller stars used up most of its fuel, it will turn into a red giant as the
core is contracted and the outer layers grow in size and becomes a red giant star.
Eventually, when the remaining energy is used up, the outer layers become loose
and form a Planetary Nebula and being blown away; a white dwarf is remained.
f. Stars more massive than ~ 6 solar masses form a red super giant. It will then
collapse and trigger a violent explosion known as a supernova.
g. After a supernova, if the remaining mass of the star is about 1.4 times that of our
Sun, the core is unable to support itself and it will collapse further to become a
neutron star.
h. If the remnant is more massive than around 3 solar masses it will probably end up
as a blackhole.
i. A blackhole = a region of space resulting from the collapse of a massive star;
extremely high gravitational field; so high that electromagnetic waves, including
visible light can’t escape out.
j. Black holes are detected as surrounding material (like gas) is funneled by the force
of gravity into a disc around the black hole. The gas molecules in the disc swirl
around the black hole so fast that they heat up and emit X-rays. These X-rays can be
detected from Earth.
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