Stars are giant balls of hot gas formed through the fusion of hydrogen into helium. They vary greatly in size, temperature, color, and stage of life. Astronomers classify stars based on these characteristics, such as by temperature (hot blue/white vs cooler red/orange) or stage (young dwarf stars vs older supergiant stars). Stars are born from collapsing clouds of dust and gas, begin nuclear fusion, and eventually die when they run out of fuel to burn.

1. Characteristics of star

2. •A star is a great ball of gas
formed mostly from
elements hydrogen which
is converted to helium
through a thermonuclear
reaction called fusion.

3. •A star is huge sphere of very
hot glowing gas.
•When stars are grouped
together we call the
constellations.
•The Big Dipper is constellation
that we see often.

4. •Classifying of
Stars

5. •Stars are classified
according to their
temperature and
brightness.
•Hot Stars are Blue or White
•Coolest Stars are Red or
Orange

6. •Classifying Star
Contellation

7. • A young star is called a dwarf star
• They can be colored red, yellow,
or white.
Our Sun is a yellow dwarf
• Older Stars are called
Supergiant
They can be colored red or
blue.

8. •How Stars are
Born?

9. • Stars are formed from giant clouds of
dust and gas.
• Then, from gravity, the clouds collapses
into a rotating gaseous ball.
• Once of the new star get hot enough it
will begin to create energy from a
process called nuclear fusion.
• This created energy allows the star to
glow for billion of years.

10. •Where stars are
born ?

11. • The Eagle Nebula

12. •The Death of
Stars

13. •A star dies when it
runs out of gases to
burn.
•The stars will first
expand into a red,
super giant.

14. •Brightness

15. • Brightness is related to the distance
from the earth and the age of the
star.
• Hipparchus developed the idea of
classifying stars by their brightness.
1st magnitude stars are the
brightness.
6th magnitude stars are the
weakest.

16. •Apparent Magnitude- refers
to the brightness of a stars as
it appears to as.
•Absolute Magnitude- refers
to the actual amount of light
given off by a star at a
standard distance

17. •Color

18. • Cool stars (i.e., Spectral Type K and
M) radiate most of their energy in
the red and infrared region of the
electromagnetic spectrum and thus
appear red, while hot stars (i.e.,
Spectral Type O and B) emit mostly
at blue and ultra-violet wavelengths,
making them appear blue or white.

20. Asltronomers

21. • Astronomers prefer to express star
colors in terms of a difference
in magnitudes, rather than a ratio
of fluxes. Therefore, going back to blue
Bellatrix we have a color index equal to
• B - V = -2.5 log (Fb/Fv) = -2.5 log (1.22) =
-0.22,
• Similarly, the color index for red
Betelgeuse is
• B - V = -2.5 log (Fb/Fv) = -2.5 log (0.18) =
1.85

23. •Temperature

25. • The strength and pattern of the absorption lines
does vary among the stars. Some stars have strong
(dark) hydrogen lines, other stars have no
hydrogen lines but strong calcium and sodium
lines. Are their abundances different? No. When
scientists learned more about the physics of the
atom, they discovered that the temperature of the
star's photosphere determines what pattern of
lines you will see. Because of this, you can
determine the temperature of a star from what
pattern of absorption lines you see and their
strength. As a way to check this, the spectra from
all of the gas clouds from which stars form show
approximately the same abundances everywhere.

27. •The size of stars varies from a
diameter of about 16
kilometers to a diameter far
larger than the sun's. Some of
the largest stars have
diameters 1,000 times the
size of Earth's. Antars is about
600 times the size of the sun.

28. •Distance

29. • It is crucial to be able to measure
the distances to stars if we are to
derive intrinsic luminosities.
There are several methods for
measuring distances to stars, but
the most reliable by far (when it
can be applied) is Trigonometric
Parallax.

30. • Our solar system is in a region of
the Milky Way galaxy where stars
lie about 4-5 light years apart.
Elsewhere in the milky way,
distance between the stars can be
greater or smaller. In certain
group of stars, stars can be less
than 0.01 light year apart.