Stars, Galaxies & Constellations

1. Stars, Galaxies & Constellations

2. travel in waves speed of light 300,000 km/s 186,000 miles/sec white light contains all colors black is the absence of color Light

3. refracts light Spectra colorbands you see with a spectroscope continous spectrum all colored given off by glowing objects emission spectrum Used to tell the composition of hot objects Fingerprint absorption spectrum Used to tell the composition of cooler objects Spectroscope

4. The shifting in wavelength due to the motion of the object Away = red shift Toward = blue shift Can tell us if a star is moving away or towards us and how fast it is going. Doppler effect

5. Stellar Movement • East to west • Due to west to east rotation • Polaris doesn’t move all other stars revolve around it • Elevation in the sky is determined by Earth’s revolution around the sun

6. Constellation • Ancient astronomers saw patterns • 2450 B.C.E. • most named after mythology • 88 named constellations

7. Circumpolar seen year round revolve around polaris in the northern hemisphere northern or southern ex) ursa major (big dipper) ursa minor (little dipper) cassiopeia Seasonal seen only at certain times of the year due to Earth’s revolution Examples orion = winter lyra = summer can be seen during solar eclipse Types of Constellations

8. astronomical unit used to measure close distances within the solar system example Jupiter = 5.2 AU’s equal to the distance from the Earth to the sun 150,000,000 km light year used for larger distances the distance light travels in a year 9,500,000,000,000 km next closest star Proxima Centauri 4.2 LY Distances

9. Distances Cont. • Parsec • 3.258 light years • 30,860,000,000,000 km • use parallax to find the distances

10. Luminosity • how bright a star is • determined by it’s size and temperature • Magnitude • Two types • Apparent • Absolute

11. how bright they appear to be in the sky Ranked lower numbers equal brighter each number differs by a factor of 2.5 a 1 is 2.5 times brighter than a 2 a 1 is 6.25 times brighter than a 3 we can only see up to a sixth magnitude star with our naked eye Examples sun –26.7 Sirius –1.45 Apparent Magnitude

12. true brightness when view from the same distance from Earth 10 parsecs from Earth Examples Sirius +1.42 Sun +4.83 Absolute Magnitude

13. vary in brightness days to years Reasons pulsating stars expand and contract expand = cool = dim contract = hot = bright Types Cepheid Variables nonpulsating stars two stars revolving around one another “eclipsing binaries” Variable Stars

14. Composition mostly hydrogen and helium determined by spectral analysis Mass hard to tell look at gravity influence more mass = more gravity measured in solar masses how it compares to the mass of our sun Properties of Stars

15. size varies more than mass some smaller than Earth some 2000 times larger than the sun Density vary tremendously Betelgeuse 1/10,000,000 as dense as the sun Others 1 tsp = more than a ton More properties

16. Temperature color depends on temperature cool = red hot = blue/white divided into spectral classes More Properties

17. Birth of a Star • Starts as a nebula • cloud of gas and dust • Outside force starts movement • Shrinks • spins faster • Builds up heat • Fusion starts • Is now a star

18. h-r diagram main sequence 90% Sun Giant Brighter diameter 10 – 100 times sun super giants Brightest diameter more than 100 times the sun white dwarfs end of life were red giants lost outer layers only core left Lifecycles

19. depends on size sun sized uses up hydrogen fuel in the core Shrinks loss of outward force Increased Pressure produces heat Helium starts to fuse Into Carbon & Oxygen star expands red giant outer layer blow away Due to low gravity too far out for gravity to keep core gets left white dwarf Death of A star

20. fusion process do not stop at carbon goes till iron expands to a super giant iron core does not produce energy absorbs it Star Collapses no outward force creates a shockwave that blasts off the outer layers Supernova 10 – 100 times as bright as the sun leaves behind neutron star core collapse electrons into core trillions times more dense than the sun spin to form pulsars Death of a massive star

21. must start out 15 times as massive as the sun gravity is so strong not even light makes it out densest object some feel there is a massive black hole at the center of the milky way galaxy Formation of a Black Hole

22. million or billions of stars moving together as a unit 50 – 100 billion galaxies in the “observable universe” we live in the milky way galaxy several billions of stars all stars you see are part of it Diameter - 100,000 ly Thickness - 10,000 ly local group a group of 30 galaxies that the milky way is a part of Types Spiral elliptical irregular Galaxies

23. big bang model 10 – 20 bill years ago all matter was in a hot dense state that started to expand rapidly and cool condensed into what we have today did not expand into space created it light elements first then heavy ones Evidence Expansion red shift Cosmic background radiation Origin of the Universe