1) Astronomy is the scientific study of celestial objects like stars, planets, comets, and galaxies. 2) There is evidence that the universe began in a massive explosion called the Big Bang around 13 billion years ago, and has been expanding ever since. 3) Key evidence for the Big Bang theory includes the Doppler effect, which shows that distant galaxies are moving away from us, and the discovery of cosmic microwave background radiation filling the universe.

1. Unit 2: Astronomy Earth Science- Ms. Gill Note Packet #3A
Name: ___________________________ Period: _____ Date:__________________
Page #___
A. What is Astronomy?
Astronomy is the scientific study of matter in outer space, especially the positions,
dimensions, distribution, motion, composition, energy, and evolution of celestial objects
and phenomena. (phenomena: is a hard to explain or almost magical occurrence)
B. There are many different Celestial Objects in our Universe
Celestial objects appear in the sky during day and night. They include:
-The Sun -The Moon
- Planets -Stars
-Comets -Asteroids
-Meteorites -Black Holes
C. But where did these objects originate?
-This Big Bang, which actually sounded more like a low hum, is estimated to have
occurred between 12-15 billion years ago!!!
-According to the Big Band Theory, all the matter in the universe started out as a
single point! That point was extremely dense. It became unstable and exploded
outward.
-Today the universe continues to expand this is called Hubble’s Law – which states
that nearby galaxies are moving away slowly while more distant galaxies are moving
away more quickly.

2. Unit 2: Astronomy Earth Science- Ms. Gill Note Packet #3A
L
Page #___
D. The Universe is still expanding! Here is the proof!
Scientists have two major pieces of evidence that support the Big Bang Theory.
1) The Doppler Effect
2) Cosmic Background Radiation
Figures A & B: Raisin bread analogy of
the expanding universe
E. So what is the Doppler Effect?
When an object is moving relative to an
observer it distorts the way the observer
perceives the object’s electromagnetic
radiation. Whoa! What does that mean? Think
about when an ambulance drives by, going very
fast. The pitch of the siren changes as the
ambulance approaches you and passes you.
This is because the sound waves’ frequency is
increased as it approaches you and decreased
as it drives away. Visualize this concept using
this diagram and the animation on my eboard.
In 1929, Edwin Hubble observed a similar phenomenon
occurred with the light emitted from stars.
He discovered that if an object is moving toward
earth it’s light shifted toward the blue end of the
electromagnetic spectrum since the wavelength is
“squeezed together” producing a shorter wavelength.
This is called blue-shift! (Blue to You)
But if the object is moving away from earth, its light
is shifted toward the red end of the spectrum, since
the wavelength is “stretched out” making it longer.
This is called Red-shift! (Red Away)
All galaxies show red-shift in their spectra,
meaning they are moving away from us.

3. Unit 2: Astronomy Earth Science- Ms. Gill Note Packet #3A
Page #___
F. How big is the Universe?
It is very humbling to contemplate the size of our Universe because it is unbelievably
BIG and therefore it can make you feel VERY small. However it’s also impressive that
our civilization has acquired such great knowledge, and it reminds us that we as people
are a part of larger system. It is important for us to respect the natural equilibrium
of our planet and the universe to whom it belongs. We must work to limit our
environmental impact and continue to educate our peers about the delicate balance of
this system.
G. Measuring Distance: In order to grasp and describe the vast size of our Universe,
we must first develop a measurement standard.
• Distances between celestial objects are extremely large.
• Rather than miles, astronomers refer to a ____________________ as a
standard unit of distance.
• One light-year is the distance light travels in one year.
• The speed of light is 186,000 mps (300,000 kps).
• Thus, one light-year is about 6 trillion miles.
• The nearest star to us (Proxima Centauri) is 4.2 light-years away.
Astronomical unit:
• Another unit of distance is the _________________________ (AU).
• One AU is the distance from the Earth to the Sun (93 million miles)
• Distances to other objects are given in multiples of AU.
What is (approximately) the size of the solar system?
Have you ever heard someone say that you’re seeing the past when you look up at the
stars? It sounds romantic and perhaps even silly, but it is correct. For example, when
an astronomer views the Andromeda galaxy, he/she is seeing how it was 2.5 million
years ago. This is because it has taken that long for the light to reach us here,
offering a window into the past that no history book ever could!
H. Did you know…
A light year is the distance light travels in a single year – 9,460,528,000,000
kilometers. So the light we see coming from Proxima Centauri left the star 4.2 years
ago. Even being the nearest star, Proxima Centauri is incredibly far away. It would
take our fastest spacecraft more than 50,000 years to make the journey.

4. Unit 2: Astronomy Earth Science- Ms. Gill Note Packet #3A
Page #___
I. Components of our Universe.
The best definition of the Universe is: EVERYTHING!
We are all apart of the universe along with everything else you can think of.
Outside of the edge of the universe is nothing. This is confusing because its hard to
imagine “nothing”. The universe is expanding into nothing because nothing is in it’s way.
All matter makes up the universe.
I like to think of the components like a system of “Russian Dolls.” These components
are organized from largest to smallest and they fit inside of each other:
The universe is made of billions of Galaxies
Galaxies are made of billons of Stars
Stars are the Center Solar Systems
Solar Systems are made of planets, moons, comets, asteroids and meteorites.
Planets moons comet, asteroids and meteorites are made of matter.
J. Galaxies
A ______________ is a collection of
millions or billions of stars. Galaxies
can be spiral, elliptical, spherical or
irregular in shape. The Sun is part of
the _________ galaxy, which is a
spiral galaxy. The Sun is located on
one of the spiral arms, far from the
galactic center. When you look up on a
clear night there is a hazy lighter
band that runs across the sky. When
you look at this band you are looking at
the side of the spiral arm that is
adjacent to the arm that our sun is in.
Each arm is made of millions of stars.
The stars themselves are too far away
to see individually, but together their
light combines to make the sky lighter
in that area.

5. Unit 2: Astronomy Earth Science- Ms. Gill Note Packet #3A
K. Billions of Stars make up a galaxy, but what is a Star… are they all the same?
Page #___
Must Know Facts about Star Characteristics
A) A star is a huge, shining massive ball of gas in space that produces a large amount of
light and energy.
B) About 75% of stars are apart of groups that orbit each other.
C) They are grouped in large structures called galaxies. (Milky Way).
D) Stars have life-cycles like humans.
E) A stars color depends on surface temperature.
F) Stars vary in their size, mass, density, temperature and composition.
G) ____________________ is the actual brightness of a star.
H) Luminosity depends only a star’s _____________ and __________
I) Most stars have planets that orbit them because of their immense gravity
Composition
Stars are primarily made of
__________________ and Helium.
Many other elements are present in stars
in small amounts. A star’s composition can
be determined by
___________________________.
Spectral Analysis
_____________________ is the
study of the electromagnetic spectrum
emitted by a star, using a
_______________________.
Each element in the star emits radiation
is a specific set of ______________
Color and Temperature
 A Star’s color that we see with the
naked eye depends upon its surface
temperature.
 As materials become hotter, their
color changes from:
Red to Orange to Yellow to White to Blue
What color are the stars in the
Constellation Orion? (ESRT p 15)
Betelgeuse is ________
Rigel is ____________
How Do Stars Radiate Energy?
A stars energy is the result of nuclear
fusion, in which Hydrogen atoms combine
to form Helium atoms, releasing energy.
This Electromagnetic energy is radiated by
stars.

6. Unit 2: Astronomy Earth Science- Ms. Gill Note Packet #3A
The Main Classifications of Stars:
______________
______________
______________
______________
______________
Our Sun is classified as a
__________________
__________________
The H-R Diagram
The Hertzsprung-Russell
(H-R) Diagram on the right
is a graph of stars, comparing
luminosity and temperature.
Stars are categorized according
to these two properties!
Page #___
The H-R Diagram
• The Main Sequence is the band
into which most stars fall. They
lie somewhere in between a:
High temperature, high luminosity
&
Low temperature, low luminosity
• Red Giants and Supergiants –
cooler, very luminous stars that
are very large
• White Dwarfs are hotter, low
luminosity stars that are small
Star Life Cycles
• Stars are born in a cloud of gas and dust,
called a _________________.
• Most stars remain as
______________________ stars, until
their hydrogen fuel is depleted
• An average star, like the sun, would go
through the Red Giant phase, eventually
becoming a _____________________.
• A large star would become a
___________________, then explode
as a supernova. The result may be a
neutron star, pulsar or black hole.

7. Unit 2: Astronomy Earth Science- Ms. Gill Note Packet #3A
The Main Classifications of Stars:
______________
______________
______________
______________
______________
Our Sun is classified as a
__________________
__________________
The H-R Diagram
The Hertzsprung-Russell
(H-R) Diagram on the right
is a graph of stars, comparing
luminosity and temperature.
Stars are categorized according
to these two properties!
Page #___
The H-R Diagram
• The Main Sequence is the band
into which most stars fall. They
lie somewhere in between a:
High temperature, high luminosity
&
Low temperature, low luminosity
• Red Giants and Supergiants –
cooler, very luminous stars that
are very large
• White Dwarfs are hotter, low
luminosity stars that are small
Star Life Cycles
• Stars are born in a cloud of gas and dust,
called a _________________.
• Most stars remain as
______________________ stars, until
their hydrogen fuel is depleted
• An average star, like the sun, would go
through the Red Giant phase, eventually
becoming a _____________________.
• A large star would become a
___________________, then explode
as a supernova. The result may be a
neutron star, pulsar or black hole.