Star Classification
Classifying Stars
 What are some ways that we could group these stars? How do
you think scientists group stars?
Analysis Questions
 How did your lab group choose to classify the
stars?
 What additional ways do you think that scientists
classify stars?
 What did you notice about the star’s color and
temperature?
We Classify Based on
Characteristics
 Stars are huge balls of glowing gas
that produce energy through
fusion.
 Stars looks so small because they
are so far away.
 Only a few thousand stars can be
seen without a telescope.
 Light Year – the distance that light
travels in one year.
 Equivalent to 9.5 trillion kilometers
or 24 trillion miles.
 Sun is our closest star, and the next
closest is Alpha Centauri which is
4.3 light years away.
Brightness
 Some stars are brighter than others.
 The distance between the star and Earth, and
the amount of light a star gives off
determines the star’s brightness.
 Stars close to Earth can appear bright, even if
they do not give off much light. Additionally,
very bright stars may appear faint if they are
far away.
Apparent magnitude: brightness of the star as it
appears from earth
Absolute magnitude: the brightness of the star
determined scientifically
Distance
 Parallax – the apparent shift in position of an object when
viewed from different locations.
 This is how we determine a star’s distance from us.
Size
 The diameter of the Sun is about 100
times larger than the diameter of the
Earth.
 The mass determines how big a star will
become.
 Stars can be bigger than the Sun!
 Giant and Supergiant stars are larger.
 Betelgeuse is 600 times greater in
diameter than the Sun.
 Stars can be smaller than the sun!
 White dwarfs are smaller than the Sun.
 About 100 times smaller than the Sun’s
diameter.


Size of Earth
The sun will end its life as a black dwarf.
Color and Temperature
 Stars vary in color. These differences are because of the
difference in temperature.
 We group stars by color.
 Blue  White Yellow  Orange  Red
 As you read colors from left to right, blue is the hottest star to red
the coolest temperature.
Hertzsprung–Russell diagram
Based off of this data, what is the
best way to classify these stars?
 A. Color
 B. Temperature
 C. Brightness
 D. Size
Star #
Known Information
45
6,000 degrees Celsius
78
7,000 degrees Celsius
239
10,000 degrees Celsius
789
8,000 degrees Celsius
7855
1,000 degrees Celsius
391
7,000 degrees Celsius
Based off of this data, what is the
best way to classify these stars?
 A. Color
 B. Temperature
 C. Brightness
 D. Size
Based off of this data, what is the
best way to classify these stars?
 A. Color
 B. Temperature
 C. Brightness
 D. Size
Star Classification Wrap-up
 Stars are divided into five (5) main groups: Neutron Stars,
Dwarf, Medium-sized, Giants and Supergiants
 Composition (what stars are made of) is determined by the
use of a spectroscope. This instrument breaks up the
visible light into its chararteristic colors.
 Hydrogen is the most common element in a stars
composition. Helium is the next most common element.
These 2 elements compose approximately 96-97% of a
star.
Star Classification Wrap-up
 The color of a star is determined by its surface temperature.
What are the colors from the hottest to the coolest?
 The brightness of a star depends on its size, temperature and
distance from the Earth.
 Nuclear fusion is the process of changing (or fusing) atoms of
hydrogen into helium atoms. During this nuclear fusion
process, energy and light are also created which is why a star
shines.
 The Hertzprung-Russell Diagram shows the direct correlation
between the stars absolute magnitude and its temperature.
Exit Ticket
 1. How is a star’s temperature related to its color?
 2. Is a blue star hotter or cooler than a red star?
 3. What are two factors that impact how bright a star
appears to us on earth?
 4. What is the apparent magnitude of a star?