Unit 3 Astronomy
 Each
element and type of star has a
unique pattern of color in a
spectroscope
 Spectroscope: An instrument that
separates light into its component
colors- similar to what a prism does to
light
Red-shift: movement of spectral
(“rainbow”) lines of distant stars toward
the red end of the spectrum (“rainbow”);
AKA: Doppler shift
 Evidence that distant galaxies are
moving away from us
 The more distant the galaxy, the greater
the red shift

Sample Regents Question
In the diagram below, the spectral lines of hydrogen gas
from three galaxies, A, B, and C, are compared to the
spectral lines of hydrogen gas observed in a laboratory.
A) Galaxy B is moving away from Earth, but galaxies A and C
are moving toward Earth.
B) Galaxy A is moving away from Earth, but galaxies B and C
are moving toward Earth.
C) Galaxies A, B, and C are all moving away from Earth.
D) Galaxies A, B, and C are all moving toward Earth.

Other Proofs
 Can
still hear the sound of the
original Big Bang using sensitive
receivers
 The use of the Hubble Space
Telescope and other instruments
have led to the predicted age of
the universe: 13.7 billion years
Size of the Universe- FYI
(do not write)
Light-year: the distance light can travel
in 1 year, which is about 6 trillion
kilometers
 It is assumed that no object or energy
can travel faster than light
 Light could circle the Earth 7 times in 1
second
 The universe is thought to be about 25
billion light-years in diameter

The Future
Some astronomers think the universe
will keep expanding forever
 Others think that gravity will eventually
cause the collapse of the universe in a
big crunch
 Recent observations have led to the
belief that the universe is expanding at
an increasing rate

Unit 3- Astronomy
Structure of the Universe

The universe includes everything we
know and don’t know
Galaxy
Galaxy- includes billions of stars and
various amounts of gas and dust
 Each galaxy will have over 100 billion
stars, and there are billions of galaxies
 Type of galaxy is based on shape:
elliptical (football-shaped), irregular, and
spiral
 The Milky Way galaxy is a spiral galaxy,
which has over 200 billion stars

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Along with the Earth rotating on its axis and
revolving around the sun, the Earth is also
revolving around the center of the Milky Way
galaxy
Period of Revolution Around the Milky Way: 220
million years
Neighbor: Andromeda Galaxy
Takes 2 million years for the light from Andromeda
to reach us
Andromeda is one of about 30 galaxies in our
local group
Solar System
 Solar
System- includes a star (like the Sun)
and those celestial objects bound to it by
gravity
SAMPLE REGENTS QUESTION
In which one of the following lists are
celestial features correctly shown in order of
increasing size?

A) universe -> galaxy -> solar system -> planet
B) galaxy -> solar system -> universe -> planet
C) planet -> solar system -> galaxy -> universe
D) solar system ->galaxy -> planet ->universe
DON’T FORGET UGSS!
Universe
(largest/oldest)
 Galaxy
 Solar System (smallest/youngest)