Stars are massive spheres of hot gas held together by gravity, mainly composed of hydrogen. Stars generate their own energy through nuclear fusion and have lifecycles where they evolve, burning hydrogen and building heavier elements. The nearest star to our solar system is Alpha Centauri. Stars can be classified based on their temperature, which determines their color, from hottest and bluest to coolest and reddest. Distance to stars can be estimated using stellar parallax. Nebulae are clouds of gas and dust where new stars are forming.

1. 6. STARS

2. Stars are massive, luminous
sphere of hot gas cloud, held
together by gravity, main element
is Hydrogen. Stars
Properties of
1. generate energy by itself
2. Have an evolution to build a
massive element such as Helium
, Lithium and Beryllium
The nearest star to Solar
system is Alpha Centauri

3. Star-forming region in Orion’s
Belt

4. newly-formed star
clusters

5. Cloud Collapse - occurs deep in cloud

6. “Pillars of Creation”
Visible light - Hubble Near Infrared light
Space Telescope (HST) - ESO Very Large
Telescope (VLT)

7. “EGGS” (Evaporating Gaseous Globules)
Dense regions forming new stars -
surrounding gas & dust “eaten into”
by strong stellar winds, UV photons
& ionization fronts

8. QuickTime™ an d a
Sorenson Video deco mpressor
are need ed to see this p icture .
IR (infrared) sees
deeper than visible
light & detects thermal
emission of warm dust

11. Dark clouds &
deeply embedded
young stars with
gas outflows and
Herbig-Haro (HH)
objects

12. Some
young
disks & jets
revealed

13. “proplyds”
(protoplanetary disks)
seen in star-forming
regions

14. 6.1 Stars Evolution
The formation of a star begins
with gravitational instability within
the nebula.
When the hot cloud has
approximately reached the stable
condition of hydrostatic
equilibrium, a Protostar.

15. • Low mass stars , not much light ,
use less fuel , have a long life and
end up not a bomb.
• Massive stars that are very light
and fuel consumption rate is very
high. Will have a short life span.
And ending with a violent
explosion called a supernova.

16. Mass of protostar (M) Star Evolution
comcompare with Mass
of the Sun M
M ≥ 25 M Blue giant star
Final : Black
Hole
9M ≤ M ≤ 25M Blue giant star
Red giant star
Final : Neutron
Star

18. Conclusio
n:
Super massive
Stars
Blue giant star
Supernova
Black hole
Nebula

19. Massive Stars
Red Giant Star
Supernova
Neutron Star +
Nebula

20. Small star
Red giant star
white Dwarf
planetary
nebula

21. 6.2 Birth and
evolution of the Sun

22. G2
5,000 10,000
100
1
100

24. 6.3 Brightness and
Magnitude
Brightness
1
Magnitude

25. 1
2.512
5 2.512 5
100
-26.7
-4.5
-0.5
0.45
1.2

26. Apparent magnitude
describes the relative
brightness of objects as they appears
in sky from the Earth.
Absolute magnitude
the apparent magnitude it
would have if it were at a distance of
10 parsecs (32.6 light-years) from
Earth.

27. 6.4 Color and
Temperature

28. Color of the star related to
surface temperature
, is divided in 7 Spectral
type.
And related to lifetime of
stars. ( ) that
the youngest stars is Blue , the
oldest stars is Red.

30. O O 9.5
30,000
B 30,000- B3
10,000
A 10,000- A2
7,500
F 7,500- F5
6,000

31. 6.5 Determination
of Distance
Parallax)
2

32. •
• Parsec” Parallax Angle of 1
Arc Second
AU
•

34. •
r = 1/p
r= distance)
pc)
p= parallax angle)

35. Regulus)
r = 1/p
= 1/(0.04)
x 3.26 = 81.5
x 206,265 = …………….
AU

36. 6.6 Nebula

37. 1.
Great Nebula)
•
M42

39. 2.
•
•
IC 434

41. 3.
•
• Charles Messier
M1

43. 4.
•
Monoceros)
• NGC 2237

45. 5.
Trifid Nebula)
•

47. The Pleiades

48. 6.7 Stellar system
1. Binary star systems: two stars are
gravitationally bounded and they
orbit each other ex. Sirius , Procyon
2. Triple star systems : Alpha
Centauri A,B,C
3. Star cluster ex. The Pleiades ,
Great Globular Cluster in Hercules
M13.

49. 6.8 Mass of
the Stars
• Mass is the matter of the Star
• Tiny Star have low gravitational
force, low pressure of hot gas,
useless fuel.
• Measuring the mass of distant
stars is Newton’s version of
Kepler’s Third Law of orbital
motion because motion period