1. Unit 2- Stars

2. Stars Earth circles the sun (star). Billions in space
To measure distances between stars we a distance measurement called the Light- year.

3. Light-Year 1 light-year is the distance light travels in one year.
Light moves at 300,000 km/sec
That’s 186,000 mile/sec
Nearest star is 4.3light years away

4. Binary Stars
Most stars are found in pairs that revolve around each other

5. Nova A star getting suddenly brighter Occurs in a binary star system
Gases from one star are pulled into the other.
Causes a nuclear explosion.

6. Nebula Gas and dust clouds in space. Most can’t be seen
If they reflect light from nearby stars they can be seen
Probably the birthplace of new stars

7. Activity on the Sun Storms on the sun: Prominences Solar Flares
Sunspots

8. Prominences- Loops or arches of gas that rise from the chromosphere

9. Solar Flares- Bright bursts of light, huge amounts of energy released

10. Sunspots- Dark areas on the suns surface in the lower atmosphere

11. Stars Characteristics
Are formed by the same forces
Have different
Size
Composition
Temperature
Color
Mass
Brightness

12. Size 5 main categories Medium sized - like our sun
from 1/10 size of sun to 10 times it’s size
Giant stars- 10 to 100 times bigger than the sun
Supergiant stars- 100 to 1000 times bigger than the sun

13. Size White dwarfs- smaller than 1/10 the size of the sun
Neutron stars - smallest stars - about 16 km in diameter

14. Composition of Stars
Determined with a spectroscope by the colors of light it gives off
The lightest element Hydrogen makes up % of a star
Helium is second most
96-99 % is hydrogen and
helium
rest is other elements

15. Temperature Color also indicates temperature hottest surface 50000 °C
Coolest 3000°C

16. Brightness Magnitude - measure of brightness
Apparent magnitude - how bright it looks from earth
Absolute magnitude - how bright it really is
Variable stars - brightness changes from time to time

17. Hertzsprung-Russell Diagram
Found that as temperature increased, so did absolute magnitude(brightness)
90% of stars followed this pattern
Called main sequence stars
Other 10% were once main sequence stars but have changed over time

19. Distance to Stars One method is parallax
Apparent change in position as the earth goes around the sun
Parallax works only to 100 light-years

21. Why Stars Shine Stars are powered by nuclear fusion
Hydrogen atoms join to form helium
Because gravity pulls the atoms in the core so close together
Energy from sun is emitted as either light, heat, UV or x- rays

23. Corona- Outermost layer
Temp=1,700,000ºC
Few particles
Chromosphere-
middle of atmosphere
Temp =27,800ºC
1000’s of km thick

24. Photosphere-
Temp=6000ºC
550 km thick
Surface of the sun
Core-
1,000,000ºC
15,000,000ºC

25. Nebulae
Huge cloud of gas and dust in space
Used to form new stars

26. Star Life Cycles Stars change over time New stars form from nebulae
Gravity pulls the dust and gas together
Mostly hydrogen
Forms a spinning cloud

27. Star Life Cycle
When the temperature reaches 15,000,000 °C fusion begins
Makes a protostar - a new star
What determines the life cycle of the star is how much mass it starts with.

28. Medium-Sized stars
Shine for a few billion years as hydrogen turns to helium.
Helium core shrinks and heats up
Outside expand and cool
Gives off red light
Becomes red giant

29. Medium-Sized Stars Helium in core turns to carbon
Last of hydrogen gas drifts away to become a ring nebula or a planetary nebula.
When last of helium is used up the core collapses and becomes a white dwarf
Incredibly dense- a teaspoon will weigh tons

30. How long It depends on the mass. Smaller stars take longer
From a few to 100 billion years for medium sized stars
The sun will take about 10 billion years

31. Massive Stars Start with at least 6 times the mass of the sun.
Become red giants
The helium in the core becomes carbon and gets hotter.
Carbon atoms fuse to form oxygen, nitrogen and iron

32. Death of Stars
Stars become black dwarfs, neutron stars or black hole depending on its mass.
3 Categories:
Sun-like Stars
Huge Stars
Giant Stars

33. Sun-like Stars
Up to 1.5 times the mass of the sun

34. Huge Stars
1.5-3 times mass of the sun

35. Giant Stars
Over 3 times the mass of the sun

36. Black Dwarf White dwarf- staple star; no nuclear fuel
When all fuel is released turns into a black dwarf

37. Neutron Stars Stars that start out up to 2-8 times the mass of the sun
The core of the exploding star collapses and becomes a neutron star. (Protons and Electrons combine to form neutron.)
As massive as the sun, but only 16 km across.
Give off pulses of radio waves
If these radio waves come in pulses it is called a pulsar

38. Black holes If the star was bigger than 30 times the mass of the sun
The left over core becomes so dense that light can’t escape its gravity.
Becomes a black hole.
Grab any nearby matter and get bigger
As matter falls in, it gives off x-rays.
That’s how they find them