Earth Science
Chapter 2
Astronomy: Stars and Galaxies
Cosmology: The study of the universe as a whole. The “Big Bang” theory.
A.
B.
C.
Our Place in Space
1. Earth is the 3rd planet from the Sun (about 93 million miles
away) in a system of 9 planets, comets, and asteroids.
2. Our solar system is on one of the spiral arms of the Milky Way
Galaxy. A little over half way from the Galaxies center.
3. The Milky Way is a rather large spiral galaxy
a. Diameter: 100,000 Light Years
b. Thickness: 2,000 Light Years
*Conversion: 1 L.Y. = 9.5x10^15 m
4. Our galaxy is one of 19 other galaxies in the “local cluster”
a. Largest of local cluster is Andromeda Galaxy (2
million L.Y. away.
5. There are about 100 billion galaxies in the universe.
6. Each Galaxy has an average of about 100 billion stars.
7. On a larger scale, the universe seems to be made of large galaxy
clusters speeding away from each other.
Galaxies:
1. Spiral Galaxies (Milky Way)
a. Shaped like pinwheels
b. Most common type of galaxy
2. Elliptical Galaxies
a. flat shaped
b. very little dust and gas
c. generally contain older stars
3. Irregular Galaxies
a. No particular shape
b. Not as common
c. Closest to Milky Way
Scientific Methods and tools to measure and view the Universe
1. Spectroscope:
a. Used to break up the white light into the stars
characteristic colors.
b. Light passes through a beam sending the light to a
prism. The prism separates the light into a spectrum
showing the “true” colors of the star.
2. Measuring methods
a. The Red Shift
D.
E.
i. 1920’s Edwine Hubbe used the Hale
Telescope to discover that some of the
“nebula” observed were actually distant
objects outside of our Milky Way.
ii. These distant galaxies had spectral lines
which shifted toward the red end of the
spectrum.
iii. The more the light is shifted to the blue or
red end of the spectrum, the faster the star is
moving toward or away from Earth
b. Doppler effect
i. The apparent change in wavelengths that
occurs when an object is moving toward or
away from Earth
ii. Example: railroad train horn
The Big Bang Theory:
1. The universe began to expand with the explosion of concentrated
matter and energy causing continual expansion ever since.
a. All the matter and energy of the universe was
concentrated in into a single place of very hot
temperatures and was very dense.
b. 15-20 billion years ago the explosion occurred (big
bang) shooting the concentrated matter and energy
in all directions.
c. Left over energy is called background radiation
i. Scientists have discovered this radiation to
be constant throughout supporting the
theory.
d. following the big bang, gravity began to pull matter
into clumps
i. these clumps became the galaxies
Possible Futures of the Universe:
1. Open
a. Matter will continue to race away from the center of
the universe causing continual expansion or eternal
universe. (be careful, eternal in this case does not
mean forever)
b. Stars will eventually die using the last of their
energy leaving a universe with “total emptiness”
c. End will not occur for billions of years
2. Closed
a. The gravitational attraction between the galaxies
will cause their movement away from each other to
slow down.
F.
G.
b. The expansion will come to a halt, and gravity will
begin to pull the galaxies back toward each other at
the center of the universe.
c. The matter will again be packed into a tight area
causing another big bang starting the process over
again.
d. May occur once every 80-100 billion years.
3. Flat Universe
a. The balance between expansion and contraction is
just right.
b. Expansion will stop, gravitational pull will not be
strong enough to pull the matter back together
c. Current evidence is pointing to this theory.
Multiple star systems:
1. Alpha Centauri – a three star system closest to Earth 4.3 L.Y.
away.
a. Proximi Centauri is the actual closest star to Earth.
2. Most common are binary stars ( two star system)
Star Characteristics:
1. Size: five main groups (smallest to largest)
a. Neutron (16 km)
b. White dwarf (distance across Asia)
c. Medium sized (our sun)
d. Giant (10-100x our sun)
e. Supergiant (1000x)
2. Mass: determined by composition of star
a. Scientists use a spectroscope (fig. 2-22 pg. 67)
b. Mostly Hydrogen (60-80% of total star mass)
c. Helium (15-39% total star mass)
d. Neon, oxygen, carbon, nitrogen (other elements 4%
composition)
3. Color:
a. Blue or Blue-white
b. White
c. Yellow
d. Red-Orange
e. Red
4. Temperature: Determined by color. (Average surface temp)
a. Blue/Blue-white = 35,000 degrees C
b. White = 10,000
c. Yellow = 6,000
d. Red-orange = 5,000
e. Red = 3,000
5. Brightness: Determined by size, temperature and distance from
Earth
a. Apparent Magnitude – brightness as seen from
Earth
b. Absolute Magnitude – Actual brightness
H.
I.
J.
K.
L.
M.
Hertzspurng-Russell Diagram (H-R Diagram)
1. A diagram of stars to show the relationship between absolute
magnitude and temperature. As magnitude increases so does the
temp
2. Main sequence stars make up more than 90 % of all stars
3. 90% of stars lives are spent as main sequence stars
Measuring Star Distance
1. Star Parallax
a. Refers to the apparent movement of the star in the
sky when in fact the Earth is the only thing moving.
See fig. 2-26
b. This is a good method for stars less than 100 light
years from Earth
2. Brightness and apparent magnitude
a. Mathematical formula not as accurate as star
parallax and only can be used for start up to 7
million L.Y. away
3. Spectroscopes
a. Scientists measure the amount of red shift and use a
complex mathematical formula…controversial.
Shiny Stars:
1. Stars core contain extreme gravity
2. Gravity pulls the inner core atoms so close they fuse together
called NUCLEAR FUSION.
a. During nuclear fusion, two hydrogen atoms fuse
together and form Helium and energy (in the form
of heat and light)
i. X-ray, infrared, ultraviolet, radio and visible
light
Nova:
1. A star that suddenly increases in brightness for a few hours or
days and then dims again.
2. A nova is caused by a gas given off by a stars companion star
which strikes the surface of the nova star creating a nuclear
explosion.
Nebulae:
1. Massive clouds of dust and gasses which are the birth places of
new stars.
2. Light given off by nebulae include x-ray, ultraviolet, and
infrared. (none of these are visible by the naked eye)
Evolution of Stars:
1. Protostars: (This birth of a star can take millions of years)
a. New born stars formed by nebulae hydrogen gas
spinning around and eventually causing atoms to
collide together.
b. Hydrogen gas heats up during the collision. When
the temp of the spinning cloud of Hydrogen reaches
15,000,000 degrees C, nuclear fusion begins
creating the new star.
2. Medium sized stars:
a. Life of the star is determined by how much mass it
started with.
b. They hydrogen in the core burns up leaving Helium
to shine and the core shrinks. As it shrinks it heats
up.
c. The outer core is still composed of hydrogen, the
heat of the inner core causes the outer hydrogen to
expand and cool creating a red color and a “red
giant star”.
d. When the nuclear fusion ceases in the core, the red
giant cools and gravity causes the remaining star
matter to collapse inward creating a ….
3. White dwarf:
a. Extremely dense matter left from red giant stars
b. Shines with a hot white light
c. Eventually will die out and become a black dwarf
(no light).
d. Time of death determined by size of star. The
bigger the star the sooner the death.
4. Massive Stars:
a. Have greater mass than medium sized stars
b. Continue through same cycle as medium sized stars
until they become red giants or supergiants
c. They do not become white dwarfs instead they
continue with nuclear fusion in the core until iron is
made. Iron atoms will not fuse together.
5. Supernova:
a. Iron core of Massive Star absorbs energy
b. When energy is released the star breaks apart
causing an explosion called a supernova
6. Neutron Star: (high mass)
a. Remains of a supernova spinning rapidly creating
radio waves
b. Some neutron stars radio waves can be detected in
pulses and are called pulsars
7. Black Holes: (Very High Mass)
Core of a supernova gets swallowed up by it’s own
gravity
b. It is so strong that not even light can escape
c. Thus the creation of a black hole
i. Scientists can find them by x-rays given off
of matter just before entering the hole
ii. It is unknown what happens to the matter
after it is swallowed by the black hole
1. some think the matter is squeezed
out of existence
2. others think black holes are
passageways to other parts of the
universe, to other universes, or into
time
a.