Unit 6
Astronomy
• 1.1.1 explain how the formation of the solar system created the
sequence of bodies and the relative motion that defines our solar
system
• explain the hierarchy of the solar system compared to the universe
• 1.1.2 explain how the relative motions of the earth, sun and moon
cause ocean tides
• explain the reason that Earth has four seasons based on the tilt of
Earth’s axis of rotation and Earth’s motion relative to the sun
• relate Earth’s initial formation to its present day spherical shape
• 1.1.3 explain how the sun produces energy which is transferred to
the Earth by radiation
• 1.1.4 explain how incoming solar energy makes life possible on
Earth
1.1.1 be able to describe the motions of precession and nutation & their effect on
Earth’s orbit around the sun
be able to describe Earth’s primary motions relative to those of the solar system
and galaxy
be able to demonstrate how bodies in space both create and are affected by
the gravitational attraction of adjacent bodies resulting in elliptical orbits
be able to explain barycenter
1.1.2 be able to demonstrate the relative positions of Earth to the sun during different
seasons
1.1.3 identify combustion and burning objects
describe, compare and contrast nuclear fusion and fission
be able to explain the equilibrium between gravity and particle motion in the
core of a star
navigate the electromagnetic spectrum and identify features of associated wave
energy
1.1.4 explain how the seasons are a result of the Earth’s tilted axis and the amount of
solar energy that Earth receives
Modern Astronomy
• Ancient Greeks believed:
– Geocentric Model
• theory that the Earth is the center of the
solar system
• Modern science believes:
– Heliocentric Model –
• theory that the Sun is the center of the
solar system
• developed by Nicolaus Copernicus in 1543
The Sun-EarthMoon system
Tools of Astronomy
• Light – electromagnetic radiation
– Visible light (what humans can see)
– Infrared
– Ultraviolet
– Radio waves
– Microwaves
– X rays
– Gamma rays
• Electromagnetic radiation is arranged by
wavelength and frequency
– Can be classified by either wavelength or
frequency
• Frequency and wavelength are related
c = λf
– c = speed of light = 3.0 x 108 m/s
– f = frequency
λ = wavelength
Telescopes
• 3 benefits:
– Can attach different detectors to observe all
wavelengths
– Brings much more light into focus than the human
eye
– Allow use of specialized equipment
• 2 types:
– Refracting: use lenses to focus light
– Reflecting: use mirrors to focus light
Instruments in Space
• Earth’s atmosphere blocks some infrared (IR)
radiation & ultraviolet (UV) radiation, X rays
and gamma rays
• Images from wavelengths that do pass
through Earth’s atmosphere are blurred
• Can allow for close-up observations and
collection of samples
Sun-Moon-Earth Interactions
• Daily Motion
– Rotation of the Earth
– 15o every hour
• Annual Motion
– Earth’s orbit along the ecliptic around the Sun
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Earth’s tilt
Solstices
Equinoxes
Moon phases
Eclipses
Earth’s Tilt
• Earth’s axis is tilted about 23.5o relative to the
ecliptic
– This along with Earth’s orbit gives us seasons
– Causes the Sun’s altitude to change throughout
the year
– Solstices
– Equinoxes
Solstices
Summer Solstice – around June 21
Sun is directly overhead at Tropic of Cancer
Winter Solstice – around December 21
Sun is directly overhead at Tropic of Capricorn
Equinoxes
• Autumnal Equinox – around September 21
– Sun is directly overhead at the equator
• Vernal Equinox – around March 21
– Sun is directly overhead at the equator
• Length of day and night are the same
Barycenter = center of mass
Precession
Nutation
Rotation
THE MOON
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Solid, rocky body
Radius is about 27% of Earth’s
Mass is about 1% of Earth’s
Age of the moon is about 3.1 to 3.8 billion yrs
Formation of the Moon
• 3 Theories
– Capture Theory: during the formation of the solar
system a large body got too close to the forming
Earth and got trapped by gravitational pull
– Simultaneous Formation: moon and Earth formed
at the same time in the same area
– Impact Theory: a Mars-sized object hit Earth
about 4.5 billion yrs ago during the formation of
the solar system
Lunar Surface Features
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•
•
•
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Highlands
Maria
Impact craters
Ejecta and rays
Rilles
Regolith
Phases of the Moon
Tides
• Effect of the Moon’s gravity on Earth
• Occur every 12 hours
Spring tides
higher than
normal
because the
Moon and Sun
are aligned
Neap tides
lower than
normal
because the
Moon and
sun are at
right angles
to each other
Eclipses
• Solar
– Moon passes between the Earth and Sun
• Lunar
– Moon passes through the Earth’s shadow
The Solar
system
Johannes Kepler
• Developed three laws
• Kepler’s 1st Law – planets orbit the Sun in an
ellipse (oval shape)
• Kepler’s 2nd Law – an imaginary line between a
planet and the Sun covers the same amount
of area in the same amount of time
• Kepler’s 3rd Law – the size of a planet’s ellipse
is related to its orbital period
P2 = a3
P = orbital period
a = semimajor axis
• Galileo Galilei – 1st person to use a telescope
– Discovered 4 moons around Jupiter
• Isaac Newton – developed the law of universal
gravitation
F = G m1m2
F = force (in Newtons)
r2
m1 & m2 = mass of the bodies (in kg)
G = 6.6726 X 10-11 m3/kg/s2
r = distance between the bodies (in m)
• Center of mass – balance point between two orbiting
bodies
– Between the Earth and the Sun this point is nearly on the
Sun’s surface
How the Solar System Formed
• Collapsing interstellar cloud
Terrestrial Planets
• MERCURY
Location: closest to the Sun
Moons: no moons
Atmosphere: very thin, mostly oxygen and sodium
Surface: much like Earth’s moon
Interior: solid nickel-iron core
Day Length: 58.5 Earth days
• VENUS
Location: 2nd planet from the Sun
Moons: no moons
Atmosphere: thick, mostly carbon dioxide
Surface: relatively smooth due to lava flows
Interior: liquid metal core
Day Length: 243 Earth days
• EARTH
Location: 3rd planet from the Sun
Moons: one moon
Atmosphere: thick, mostly oxygen and nitrogen
Surface: life sustaining
Interior: solid nickel-iron core
Day Length: 24 hours
• MARS
Location: 4th planet from the Sun
Moons: 2 moons – Phobos, Deimos
Atmosphere: thin & windy, mostly carbon dioxide
Surface: craters in the south, plains in the north,
ice caps at both poles
Interior: solid nickel-iron core
Day Length: almost 25 Earth hours
Gas Giants
• JUPITER
Location: 5th planet from the Sun; has a ring
Moons: 4 major – Io, Europa, Ganymede, Callisto
Atmosphere: very thick, mostly hydrogen
Surface: no true surface; gas & liquid gas
Interior: may have an Earth sized solid core
Day Length: 10 Earth hours
• SATURN
Location: 6th planet from the Sun; has many rings
Moons: 1 major - Titan
Atmosphere: thick, mostly hydrogen
Surface: no true surface, gas & liquid gas
Interior: may have a small, solid core
Day Length: nearly 11 Earth hours
• URANUS
Location: 7th planet from the Sun; has 10 rings
Moons: 2 major - Titania, Oberon
Atmosphere: thick, mostly hydrogen
Surface: no true surface, gas & liquid gas
Interior: may have a small, solid core
Day Length: 17 Earth hours
• NEPTUNE
Location: 8th planet from the Sun; has 6 rings
Moons: 1 major - Triton
Atmosphere: thick, mostly hydrogen
Surface: no true surface, gas & liquid gas
Interior: may have a small, solid core
Day Length: 16 Earth hours
• PLUTO – a planetoid
Location: 9th from the Sun
Moons: 1 moon - Charon
Atmosphere: thin atmosphere of methane and
nitrogen
Surface: mix of ice and rock
Interior: unknown
Day Length: about 6 Earth days
Galaxies and the
Universe
• Our solar system is in the Milky Way Galaxy
• Most scientists believe that
there is a massive black hole
at the center of our galaxy
• It is called Sagittarius A*
• It is thought to be about 93 million miles
across
• It is thought to weigh about the same as 4
billion Suns
Formation of the Universe
• Age is about 13.5 billion years
• Big Bang Theory (not the TV show)
– Expansion of space and matter
• Steady-state theory
– Universe looks the same on large scales
– New matter is created and added to the universe
as it expands
Death of the Universe
• Big Crunch – universe stops expanding and then
collapses back in on itself
• Big Freeze – universe never stops expanding,
becomes progressively too cold to support life
• Flat Universe – universe stops eventually stops
expanding and also becomes too cold for life
• Big Rip – rate of expansion is increasing due to
dark matter which will eventually tear the
universe apart