1. Stars and Their Characteristics
28.2

2. Constellations
Constellation- groups of stars that appear to form patterns
88 constellations can be seen from n. and s. hemispheres
So far away that only after thousands of years might the motions be observed
Big Dipper- asterism (small-star grouping)
Part of Ursa Major- Great Bear

3. Stars Polaris- north star
Doesn’t appear to move
Circumpolar stars- seem to move around Polaris because Earth rotates
Position of Earth

4. Distance to Stars Light year- distance light travels in a year
Used instead of kilometers/astronomical units
Parallax- basic way to measure star distance
The nearest stars have the largest parallax angles, while those of distant stars are too small to measure

5. Elements in Stars sphere of mostly hydrogen and helium gases
small percentage may be heavier elements (oxygen, carbon, nitrogen, etc..)
no two stars contain exactly the same elements in the same proportions
wavelengths depend on both composition and temperature

6. Mass, Size, and Temperature of Stars
mass can be determined by the inertial properties of the body or by its gravitational effect on the bodies around it
more mass = more gravitational effect
stars vary more in size than they do in mass; and even more in density
range of colors a star emits depends on its surface temperature
Blue= hottest; red = coolest

7. Luminosity and Absolute Magnitude
Luminosity (apparent magnitude)- brightness of a star at its current distance from Earth
depends on its size and temperature
Bigger stars tend to be brighter
Bluer stars tend to be brighter
absolute magnitude- measure of how bright the star would be if all stars were at the same distance from Earth
The more negative the number, the brighter the star
Object mv Mv
Sun
-26.8
4.83
Sirius
-1.47
1.41
Vega
0.04
0.5
Betelgeuse
0.41
-5.6
Polaris
1.99 -3

8. Variable Stars
variable stars are those stars that show regular variation of brightness
pulsating stars change brightness as they expand and contract
Cepheid variable- yellow supergiants whose cycles of brightness range from about 1 day to 50 days
the slower the cycle, the greater the luminosity of the star
can calculate the distances to galaxies in which they can identify Cepheid stars
non-pulsating star can change brightness because is part of a binary star system
results in eclipses

9. H-R Diagram Hertzsprung-Russell Diagram
diagram plots the luminosity of stars against their surface temperatures
most stars (90%) are in a band that runs from the upper left (high, high) to the lower right (low, low)
main sequence stars
main sequence stars vary in surface temperature and absolute magnitudes
commonality: actively fusing hydrogen into helium

10. H-R Diagram cont…
giant stars- great luminosity and diameter; x greater than sun
supergiants- higher luminosity; diameter > 100x than sun
white dwarfs- stars near end of life
once red giants that lost atmosphere

11. HR Diagram

12. Stellar Evolution Birth of a Star
begins as a nebula- cloud of dust and gas (99% hydrogen)
nebula may condense when an outside force acts upon it
particles move closer together under gravity
increase density = increase temperature
if nebula glows, called protostar
center will become hotter until fusion takes place and a star is born

13. Nebula and Protostar

14. Stellar Evolution Death of a Star (size of the sun)
remain same size (main sequence) for billions of years because energy produced through fusion equals gravitational pull
hydrogen is used up so gravity takes over, which then produces heat by contraction
entire star expands (Red Giant)
core temperature rises enough for helium to fuse into heavier elements, producing a carbon-oxygen core
surface gases are blown away, leaving core (white dwarf)
planetary nebula- glowing halo of gases
fades as gases dissipate into space leaving white dwarf behind
once all fuel is used up, the core will no longer glow, becomes a black dwarf

15. Main Sequence and Red Giant

16. White Dwarf, Planetary Nebula, and Black Dwarf

17. Stellar Evolution Death of a Massive Star
fusion process will continue until iron nuclei are formed
absorbs energy, so iron core quickly collapses
supernova- explosion that produces a brilliant burst of light
produces many elements: copper, uranium, silver, and lead
Remnants of Massive Stars
neutron star-dense mass of neutrons formed through gravity
pulsar- a distant neutron star that emits rapid pulses of light and radio waves instead of steady radiation
black hole- remnant of a star at least 15 times as massive than the sun
gravitational force is so strong that light cannot escape

18. Supernova and Neutron Star

19. Pulsars and Black Holes