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EARTH SCIENCE REGENTS REVIEW
UNIT 3 – EARTH IN THE UNIVERSE
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ASTRONOMY - The study of objects in space.
 Universe- Includes all known matter (everything).
 Celestial Object – Any object outside or above Earth’s
atmosphere.
 Galaxy- A large group (billions) of stars (held together
by gravity). Our galaxy is a spiral galaxy called the
Milky Way. Our solar system is in one of the arms of
the Milky Way.
 Solar System- The sun and all the objects that revolve
it.
1) ORIGIN OF THE UNIVERSE
A) BIG BANG THEORY – Theory that the Universe was
created from an explosion approximately 10-14 billion years
ago.
 The latest calculations now show that the universe is
13.7 or 13.8 billion years old.
 Most of the atoms were hydrogen and helium.
 The Universe has been cooling off ever since.
EVIDENCE OF THE BIG BANG THEORY
 Background Radiation – Radiation has been found
(microwaves) in all directions in the Universe.
 Electromagnetic Spectrum (Doppler Effect)
1) “RED SHIFTED” –
 Universe is expanding
 The light from a star that is moving AWAY from us
will be shifted towards the red (infrared) end of the
visible spectrum (Red Shift). Red light has a longer
wave length. Most objects are moving away from us.
 It is the space between the galaxies that is expanding.
2) “BLUE SHIFTED” –
 A star that is moving towards us will be shifted
towards the blue (ultraviolet) end (of the spectrum (
Blue Shift). Blue light has a short wavelength.
HUBBLE’S LAW
** THE FURTHER A STAR IS SHIFTED
TOWARD THE RED END OF THE SPECTRUM,
THE FASTER IT IS MOVING AWAY FROM US.
**
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2) STRUCTURE OF THE UNIVERSE
A) GALAXY – Billions of stars held together by gravity.
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We are in the Milky Way Galaxy
There are over 200 billion stars in our galaxy.
It is a spiral galaxy (and it bulges in the center).
We are located on one of the outer arms (ORION) on the left
side.
 It is approximately 100,000 light years long.
HERE WE ARE !!!
OUR SOLAR SYSTEM
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B) STARS – A large ball of gas held together by gravity.
 Our Sun is an average star (medium mass). It is
approximately 4.6 billion years old. It will live for about
another 4.6 billion years. It is composed mainly of hydrogen
(which is the most abundant element in the universe).
 Most stars live their lives on the Main Sequence. The HR
Diagram (Classification of Stars Chart – E.S.R.T.) is not a
map. It is a classification system .
LIFE CYCLE OF STARS
 THE MASS AT BIRTH DETERMINES THE PATH THE STAR WILL
LEAD (low or medium mass compared to a high mass star).
1) Stars begin their lives as Molecular Clouds called Nebula
(called stellar nurseries).
2) Protostar: forms when a nebula is dense and cool
enough to begin contracting into a star (GRAVITY).
3) When hydrogen begins to fuse into helium the
protostar becomes a star (process called Nuclear
Fusion).
4) When stars use up all of their hydrogen they begin to fuse
helium. The star expands, becoming a Red Giant (or Red
Supergiant) .
5) When the helium is used up for our sun, the star fuses
carbon, the star is now a white dwarf. The star eventually
runs out of fuel and burns out (becoming a black dwarf).
6) Large stars and binary stars may Supernova (blow up)
instead of burning out. When they supernova a black hole
or a neutron star might form.
***SOME OTHER STAR NOTES***
 Luminosity of a star measures how bright it would be in
relation to the sun if all stars were the same distance from an
observer (Absolute magnitude).
 Apparent Magnitude – This takes into account the absolute
brightness and its distance from us. This is basically “How
the star looks to us at night”.
 Light Year – The distance light travels in a year (approx 6
trillion miles).
STAR TYPES
1.
2.
3.
4.
5.
Main Sequence
Giant Stars
Super Giants
White Dwarfs
Black Dwarfs
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C) SOLAR SYSTEM
 Consists of 8 planets and one star (Sun).
1. INNER PLANETS (Terrestrial Planets)– Mercury,
Venus, Earth, Mars
 Rocky Surfaces
 High Density
 Low Mass
Note: Venus is the hottest planet due to the composition of its
atmosphere - large amounts of Co2.
Note: Asteroid Belt - The area between Mars and Jupiter
that contains asteroids or minor planets that orbit the
Sun.
2. OUTER PLANETS (JOVIAN PLANETS) – Jupiter,
Saturn, Uranus, Neptune (also called the Gas Giants).
 Gas Surfaces
 Low density
 High Mass
 Evolution of the Solar System: Scientists believe that our
solar system started to form approximately 4.6 billion years
ago (see handout on beginning of the solar system).
 Astronomical Unit – The distance between the Earth and
the Sun (approximately 93 million miles).
 It takes about 225 million years for our solar system to move
around the Milky Way Galaxy.
 Venus and Uranus rotate clockwise which is opposite of the
other planets (counterclockwise).
D) OTHER CELESTIAL OBJECTS
1. MOONS – bodies that orbit a planet (seen by
reflected light only).
2. ASTEROIDS – Rock fragments that revolve around
the sun.
3. COMETS – Loose mass of rock, ice, dust, and gas
that move throughout space together.
4. METEOROIDS – Fragments of rock that travel
through space.
5. METEORS – “Shooting Star” meteoroid that has
broken through our atmosphere.
6. METEORITE - chunk of rock that reaches Earth’s
surface.
NOTE: 1) An impact crater is when comets, meteorite, and asteroids
land on a planet and create a depression (hole) in the
crust.
2) An impact event is when comets, meteorites, and asteroids
collide with a planet.
3) PLANET MOTIONS
 ROTATION – The time it takes for a planet to make one spin on
its imaginary axis (Times vary by planet -see E.S.R.T.). (Earth
rotates from west to east looking at it from the equator and
counterclockwise looking down from the North Pole).
 REVOLUTION – Movement around the sun called an orbit.
(Times vary by planet - see E.S.R.T.). (Earth revolves around the
sun in a counterclockwise direction).
 ECCENTRICITY OF A PLANETS ORBIT – The degree of
ovalness of an ellipse.
1. Path of an orbit is called an ellipse.
2. Two fixed points are called foci.
3. KEPLERS THREE LAWS
A. FIRST LAW – All planets orbit the sun in an elliptical
orbit.
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B. SECOND LAW – Equal areas are swept (covered) in
equal times (due to velocity).
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C.
THIRD LAW – Period of revolution directly
proportional to distance from sun (The greater the
distance from the satellite you are orbiting, the
longer the period of revolution.
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*KEY NOTES*
 Maximum eccentricity = 1 (straight line).
 Minimum eccentricity = 0 (circle).

The closer you are to the object you are orbiting the faster your
speed (more KE, less PE). (We are closest to the Sun on
approximately January 3rd. This is called perihelion.
 The further you are to the object you are orbiting the slower
your speed (more PE, less KE). We are furthest from the Sun
on approximately July 4th. This is called aphelion.
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ECCENTRICITY FORMULA:
E= DISTANCE BETWEEN FOCI
LENGTH OF THE MAJOR AXIS
 APPARENT DIAMETER – The closer the object (planet) is,
the larger it looks to you (Due to elliptical orbits). (You are not
always the same distance at every point from the object you
are revolving around).
(Therefore the apparent diameter of the sun, as well as other
planets, varies in a cyclic manner ).
3) INERTIA / GRAVITY
A. INERTIA - The concept that an object at rest will stay at rest
and an object in motion will maintain the direction and speed of
that motion unless an opposing force affects it.
B. GRAVITY – Attractive force that exists between any two forces
in the universe.
 Based on MASS and DISTANCE. The closer the object, the
larger the mass – the GREATER the gravitational force.
C.
The balance of the force of inertia and gravity
creates an orbit.