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Astronomy
Earth and Moon
Solar System
Stars and Galaxies
Effects of Gravity
• Gravity – force of attraction between any
two objects
• Mass – amount of matter that an object
contains
• Orbit – curved path that an object follows
as it revolves around another object
Earth’s Movement
• Revolution – movement of one object in its
orbit around another object; a single
revolution takes about 365 days
• The various positions of the Earth in
relation to the Sun will cause seasons in
some parts of the world
• Solstices – Sun is directly on the Tropic of
Cancer or Tropic of Capricorn
• Equinoxes – Sun is directly on the Equator
Moon’s Movement
• Revolves completely around the Earth in
about 29 days
• Rotates on it’s axis about once every 29 days
• Therefore, we always see the same side of
the Moon
• Phase – change in the Moon’s appearance
as it orbits the Earth
• 4 main phases: New, First Quarter, Full,
Third Quarter
Eclipses
• Lunar eclipse – passing of the Moon
through the Earth’s shadow; Earth is
between the Sun and the Moon
• Solar eclipse – passing of the Moon
between the Earth and the Sun; Moon
casts a shadow on the Earth
Solar Eclipse
Lunar Eclipse
Tides
• Tides – regular rising and falling of the
Earth’s major bodies of water
• Moon’s gravity causes ocean water to pile
up on the side of the Earth facing the
Moon
• Other factors that affect tides are wind,
ocean temperature, and water flowing into
the ocean
Moon’s Surface
• Maria – low, flat plains on the Moon’s
surface that appear as dark areas
• Crater – circular low area surrounded by a
rim, usually caused by an object hitting the
ground
• Apollo Missions: Between 1969 and 1972,
seven trips to the Moon.
– Measure moonquakes, moon rocks and dust,
approximately 4.6 billion years old
– No other people have visited the Moon since.
The Solar System
• Star – glowing ball of hot gas that makes
its own energy and light
• Planet – large object in space that orbits a
star, such as the Sun
• Moon – natural satellite that orbits a planet
• Solar system – a star, such as the Sun,
and all of the objects that revolve around it
in space.
The Solar System
The Sun
• Made of hydrogen (H) and helium (He)
• Rotates on an axis; parts rotate at different
rates
• Temperature: Outer 5,500 °C, Inner
15,000,000 °C.
• Nuclear reactions fuse two hydrogen
atoms to make one helium atom
Parts of the Sun
• Atmosphere – envelope of gas
surrounding an object in space
• Photosphere – inner layer of the Sun’s
atmosphere that gives off light
• Chromosphere - middle layer of the Sun’s
atmosphere that can be seen during an
eclipse; has a distinctive red color
• Corona – outer layer of the Sun’s
atmosphere
• Sunspots – cooler areas of the Sun that
give off less energy
The Inner Planets
• Inner planets: Mercury, Venus, Earth,
Mars; closest to the Sun
• All are solid and have a high density
• Similar in size and have a low mass
• Rocky
Mercury
• Closest to the Sun
• Fastest moving;
revolves in 88 days
• Virtually no
atmosphere
• Many craters
• Surface Temperature:
427 °C facing Sun,
-187 °C away from
Sun
Venus
• Hottest planet:
460 °C
• Greenhouse effect:
warming of the
atmosphere because
of heat trapped by
Sun
• Rotates from east to
west; 243 Earth days
Earth
• Mild surface
temperature that
changes little
• Dense protective
atmosphere
• Only planet to
have liquid water
Mars
• Reddish color; iron
oxide
• Similar rotation with
Earth; 24 hrs, 38 min.
• Longer revolution; 687
Earth days
• Thin atmosphere;
colder
• Two moons
• Only frozen water
exists
The Outer Planets
• Jupiter, Saturn, Uranus, Neptune
• Made of frozen gas and liquid, with a small
solid core
• All have a ring system
• Large size and high mass
• Low density
• Many moons
• High gravity
Jupiter
• Largest planet
• Colorful bands of
gases where
storms take place
• Fast rotation; 10
hours
• Great Red Spot;
spinning windstorm
which has lasted
300 years
Saturn
•
•
•
•
•
Second largest planet
1000 individual rings, most visible and largest
Stormy bands of clouds along the surface
Rotates quickly; 11 hours
Revolves once every 29 years
Uranus
• Rotates on its side; once every 17 hours
• Revolves once every 84 years
• At least 11 rings and 22 moons
Neptune
• Greenish blue atmosphere because of methane
gas
• Four rings
• Great Dark Spot – as big as the Earth
• Rotates once every 16 hours
• Revolves once every 164 years
Pluto
• No longer considered
a planet; dwarf planet
• No rings and thin
atmosphere
• One moon
• Crosses Neptune’s
orbit part of the time
• Rotates once every 6
days
• Revolves once every
248 years.
Other Objects in Solar System
• Asteroids – rocky objects, smaller than a planet,
that orbit a star
• Asteroid belt – region between Mars and Jupiter
where most asteroids orbit Sun
• Meteor – brief streak of light seen when an
asteroid enters the Earth’s atmosphere and
burns up
• Meteorite – asteroid that hits the surface of a
planet or moon after traveling through space
• Comet – ball of ice, rock, frozen gas, and dust
that orbits the Sun
Asteroids
Meteors and Meteorites
Comets
Stars
• Stars shine because of a process called
fusion
• Fusion – process by which particles
combine to form a new particle
• The source of energy for the Sun is
hydrogen fusion
• By combining hydrogen atoms, the Sun
produces a constant supply of energy in
the form of heat and light.
Stars
• Magnitude – brightness of a star;
determined by distance from Earth and
amount of energy
• Apparent magnitude – how bright a star
looks
• Absolute magnitude – how bright a star
actually is if all the stars were the same
distance from the Earth
• The more negative the magnitude, the
brighter the star.
• Color – blue is hottest, red is coldest
Distance to Stars
• Light-year – distance that light travels in
one year
– 1 light-year = 9.5 trillion kilometers
• Astronomical Unit (AU) – the distance
between the Earth and the Sun
– 1 AU = 149,598,000 kilometers
• Parallax – the apparent shift in a star’s
position because the position of the Earth
– Used to measure distances of starts
Distance to Stars
The Life of a Star
• A star’s life cycle begins in a nebula, a
cloud of gas and dust in space.
• Balance between gravity and fusion.
Gravity causes a collapse, fusion causes
heat and expansion
• Main sequence star – star, like our Sun,
that is fusing gases together giving off light
and heat.
The Life of a Star
• As fusion uses up hydrogen, the star
expands to about 100 times it’s original
size – Red Giant.
• Gravity overtakes the mass of the star,
and it collapses.
• Temperature begins to increase and the
outer layer is blown off forming a nova;
brilliant explosion of a Red Giant.
• Center of nova becomes a small, white,
hot dense star – white dwarf
The Life of a Star
• Star more massive than the sun, as it uses
up hydrogen, it becomes a supergiant
• Supergiant collapses and becomes a
supernova, a brilliant explosion of a
supergiant.
• After the gases have left, a neutron star
may remain; very small, very dense star
• However, if gravity is large, a black hole
may form; a region in space with
tremendous gravity that light cannot
escape.
Constellations
• Constellation – pattern of stars seen from the
Earth
Galaxies
• Galaxy – group of billions of stars
• Our galaxy is the Milky Way galaxy
– 100,000 light years thick and 10,000 light
years wide
• Three types based on shape:
– Elliptical
– Irregular
– Spiral