1. Chapter 2 Stars and Galaxies

2. Where are you? • The Earth circles the sun • The sun is one of billions of billions of stars. • To measure distances between stars we a distance measurement called the Light- year • 1 light-year is the distance light travels in one year.

3. Light-Year • Light moves at 300,000 km/sec • That’s 186,000 mile/sec • It would reach the sun in about 5 minutes • How far would it go in a year? • Nearest star is 4.3 light years away

4. Binary Stars • Most stars are found in pairs • These stars revolve around each other • If a dim star passes in front of a bright star, it will block its light. • Called an eclipsing binary • Algol dims every 69 hours • The closest star -Alpha Centari is actually a triple star system

5. Binary System Side Top

6. Constellations • Groups of stars that appear to stay together • Zodiac • Named after gods, animals, and heroes • Stars are not necessarily near each other

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

8. Clusters • Smaller groups of stars within a galaxy • Globular Clusters- Spherical shaped with may (up to 100,000 stars) • Open clusters- less organized- with fewer stars ( hundreds )

9. 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

12. Ring Nebula

14. Galaxies • Huge collections of stars • each may contain hundreds of billions of stars • The major feature of the universe • Maybe as many as 100 billion galaxies

15. Types of Galaxies • Elliptical - round, from flat disks to spheres - contain older stars • Spiral- Flattened arms that spin around a center • Irregular- no definite shape -less common

16. Andromeda

17. Large Magellanic Cloud

18. M51

19. M83

20. Milky Way • Our galaxy • almost all the stars you can see in the sky • 100,000 light-years across • 15,000 top to bottom • 100 to 200 billion stars

21. Spectrum

22. Prism • White light is made up of all the colors of the visible spectrum. • Passing it through a prism separate it.

23. If the light is not white • Stars give off different colors of light • Passing this light through a prism does something different. • How we know what stars are made of.

24. Spectra from stars will have lines missing

25. Doppler Effect • Change in wavelength caused by the apparent motion of the source. • Cars moving by you • Same things happen to light • Light from objects coming toward you is compressed looks more blue • Light from objects away looks more red

26. Red Shift • Light from galaxies moving away

27. Blue Shift • Light from galaxies moving toward us

28. A big surprise • No Galaxies showed blue shift • All galaxies showed red shift. • Which means • All galaxies were moving away • The universe is expanding

29. The Big Bang Theory • The universe started with a concentrated area of matter and energy. • 15-20 billion years ago • Then it exploded and has been expanding ever since • Faster moving stuff traveled farther • Explained red shift

30. Big Bang Theory • Predicts energy should be evenly distributed • Astronomers did find it • Called background radiation • Evenly spread throughout the universe.

31. Gravity • Force of attraction • All objects attract each other. • Pulled matter into clumps • These clumps became bigger • became galaxies

32. Open or closed? • Two possible results of big bang. • Open universe will continue expanding • Stars will eventually lose all energy • end of universe is emptiness. • In a few hundred billion years

33. Closed Universe • Gravity will eventually pull all the galaxies back together. • Eventually all matter will come back together at the center of the galaxy • Blue shift • Packed into a area as small as a period. • Then another big bang • Every 80 to 100 million years.

34. Quasars • Quasi - stellar radio source • Quasi- means “something like” • stellar means “star” • Most distant objects in the universe -12 billion light years • Give off tremendous energy as x-rays and radio waves • as much as 100 galaxies

35. Quasars • 1 sec, enough for 1 billion years electricity for Earth • At the edge of the universe • At the very beginning of the universe

36. Another Tool • Spectroscope • Breaks the light of a star up into its colors • Called a spectrum • Kind of spectrum tells scientists • what the star is made of • which way and how fast it is moving

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

38. 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

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

40. Composition • Determined with a spectroscope • by the colors of light it gives off • The lightest element Hydrogen makes up 60 - 80 % of a star • Helium is second most • 96-99 % is hydrogen and helium • rest is other elements -

41. Blue 35,000 °C White 10,000 °C Yellow 6,000 °C Red-orange 5,000 °C Red 3,000 °C Temperature • Color also indicates temperature • hottest surface 50000 °C • coolest -3000°C

42. 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 • Cephid variables - pulsating variables- change both brightness and size

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

44. Supergiants Giants Main sequence White Dwarfs Absolute Magnitude 50000 20000 10000 6600 6000 5000 3000

45. Distance to stars • One method is parallax • Apparent change in position as the earth goes around the sun

46. Measure the angle to the star Wait half a year Measure the angle to the star Triangle tells distance

47. Distance to stars • Parallax works only to 100 light-years • More than 100 light-years they use a complicated formula based on apparent and absolute magnitude. • More than 7 million light-years they use the red shift

48. Why Stars Shine • Stars are powered by nuclear fusion • Hydrogen atoms join to form helium • Happens because gravity pulls the atoms in the core so close together • The sun turns 600 billion kilograms of hydrogen to 595.8 kilograms of helium every second • The 4.2 billion kilograms of mass are turned to energy -light, heat, UV, x-rays • E= mc2

49. The Sun • An average star • Over 1 million earth’s would fit inside • 1/4 the density of the Earth • made of 4 layers

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