Star Light, Star Bright

1
Star Light, Star Bright
2
3 Factors that determine the brightness of a star

• Temperature
• Hotter the star the brighter
  the star
• Blue..white..yellow.orange..red
• HOTTEST----------------------------------------
  ------COOLEST

3
Size

• Larger the star Brighter the Star
• Smaller the star Dimmer the Star

4
Distance

• Closer the star Brighter the star
• Further the star Dimmer the star

5
Brightness Key Terms

• Luminosity
• Apparent Magnitude
• Absolute Magnitude
• Parallax

6
Luminosity

• Definition- actual or true brightness of a star
• Total amount of energy given off
• Dependent on 2 things

Temperature
Size
6000K
6000K
6000K
10,000K
More luminous
More luminous
7
Apparent Magnitude

• Definition- how bright a star appears when seen
  from earth
• System developed where a number is assigned to a
  star based on brightness
• Smaller Brighter the star
• Bigger Dimmer the star
• Sun -28 , Full Moon -11, Polaris 7
• Hubble can see 28

8
Absolute Magnitude

• Definition- brightness of a star as if all stars
  were seen from the same distance

Earth
Earth
Sun- average star, Abs. Mag of 4.8 (less
luminous, looks brighter because closer) Rigel-
orion, Abs, Mag. of -6.4 (more luminous, further
away)
To Determine apparent magnitude and distance to
earth
9
Moving Stars?

• Parallax- the apparent change in position of a
  star due to the movement of observer

Finger left/right
10
Life Cycle of a Star
11
Life Cycle of Stars
Planetary Nebula
White Dwarf
Red giant
1
Main Sequence Star
Nebula
Protostar
Red supergiant
Supernova
Black Hole
2
Neutron Star
12
Life Cycle Introduction

• http//www.youtube.com/watch?vf_KLOFe2rDY
• http//www.youtube.com/watch?vYU6X3SPZAJo

13
Step 1 Initiation

• Stars are born in nebulae (huge clouds of gas and
  dust)
• Nebula begin to condense when an outside force,
  such as shock wave, acts upon it

14
Step 2 Pre-star

• A protostar forms when a part of the nebula
  contracts, shrinks, and pressure and internal
  temperature increases
• Protostar begins to glow where nebula is
  contracting

15
Step 2 contd A star is born

• As contraction, temperature, density, and
  pressure increase protostar gets larger and
  brighter
• Center becomes so hot fusion begins
• Once fusion begins, a star is born
• TRUE STAR

16
Step 3 Teenager star

• Internal temperature hot enough to start fusion
  at center said to be a main sequence star
• Sun is an example
• Each protostar will turn into one main sequence
  star
• 90 of stars are main sequence stars
• Vary in surface temperature and absolute magnitude

17
Fate determined by Size

• If a normal size star (Sun) follows path 1
• If star is a GIANT follows path 2

18

• Path 1

19
Step 4 Middle-aged star

• Red giant- very bright, once an average star, but
  is now close to end of life
• Has expanded to many times its original size
  (heat causes it to expand)
• Hydrogen core has turned to helium and eventually
  to carbon
• Our sun will become a red giant star in about 5
  billion years

20
Star like our sun begins to die

• Star begins to die when its core temperature
  rises to a point where fuel is used up
• A carbon-oxygen core forms
• Eventually the gases at a stars surface begin to
  blow away in abrupt bursts
• Resulting glowing halo is called a planetary
  nebula

21
Death of a star like our sun

• atoms no longer fuse, fuel is used up
• Outer gases escape leaving the core which
  collapses and shrinks
• Heat still present but will continue to escape
  for about a billion of years

• White Dwarf- small, very dense, hot star at the
  end of its life, mostly carbon with nuclear cores
  depleted (about the size of earth but heavier)

22

• Path 2

23
Step 4 Middle-aged massive star

• Supergiant- largest known type of star
• can be as large as our solar system
• rare but exists
• In a massive star, hydrogen is fused more quickly
  and fusion continues until a iron nuclei is
  formed

24
Death of a Supergiant

• Supernova- exploding star

• Elements are used up very quickly and eventually
  runs out of fuel
• Collapse of the core produces a shock wave that
  blasts the stars outer layers into space
  producing a supernova

25
Option A after a supernova

• When neutron star is first formed, it spins very
  rapidly and gives off radio waves

• After a massive star goes supernova it leaves
  behind its core (called a neutron star)
• -Neutron Star- small, dense star made of neutrons

26
Option B after a supernova

• Black Hole- a star that collapses
• How do we know they exist? Pulls gases off nearby
  stars, as gas is pulled into this nothing space
  x-rays are emitted from the gas as molecules are
  pulled in

27
Cycle continues

• Star is born from great clouds of gas and dust
• Stars mature, grow old, and die
• As a star dies, it makes new clouds of dust gas
  and dust where new stars can begin to form
• More massive a star, the shorter its life

28

• http//www.youtube.com/watch?vHfqcZdNnQ6s

29
Hertzsprung-Russell Diagram

• Graph that compares temperature and absolute
  magnitude (brightness)

30
The Hertzsprung-Russell Diagram (H-R diagram)
Cool and bright
Bright
Hot and bright
Cool and dim
Hot and dim
Sun
Dim
Cool
Hot
31
Supergiants
Cool and bright
Hot and bright
Giants
Main sequence
Cool and dim
White Dwarfs
Hot and dim