Chapter 25

1. Chapter 25 Section 1: STARS

2. Patterns of stars: Constellations • Ancient cultures used mythology or everyday items to name constellations. • Constellations: Patterns of stars in the night sky

3. Modern Astronomy Studies 88 Constellations (Most named long ago)

4. Circumpolar Constellations • Stars in the northern sky that appear to • circle Polaris in 24 hours • are visible all year Polaris or Northern Star located at end Of Little Dipper in Constellation Ursa Minor

6. Some constellations are not visible during winter, only the summer (and vise versa). example – Orion Can not see b/c daytime side is facing it.

7. Absolute Magnitude • measure of the amount of light a star actually gives off.

8. Apparent Magnitude • measure of the amount of a star’s light received on Earth

9. Fifth closest star Brightest star in N. Hemisphere Canis Major Sirius

10. Rigel • Absolute magnitude much higher than Sirius but apparent magnitude is lower because it is further away from Earth

11. - Characteristics of Stars Parallax • Parallax is the apparent change in position of an object when you look at it from different places.

12. - Characteristics of Stars Measuring Distances to Stars • Astronomers use parallax to measure distances to nearby stars.

13. Space Measurement • Astronomers measure a star’s parallax • Need to know angle that the star’s position changes and size of Earth’s orbit

14. Distance is measured in light-years • Light year: distance light travels in a year. • 300,000 km/s or 9.5 trillion kilometers/yr

15. Star Properties • Color indicates temperature • Hot stars are blue (hottest)-white • Cool stars are orange – red (coolest) • Average stars are yellow

16. Cool stars look orange or red

17. Medium Temp. Stars are YellowLike Our Sun!!!

18. Also known as Sol (Roman God) The Sun’s official symbol.

19. - Characteristics of Stars Star Size • Stars vary greatly in size. Giant stars are typically 10 to 100 times larger than the sun and more than 1,000 times the size of a white dwarf.

20. Sizes of Stars

21. Star Sizes

23. THE SUN Closest star to the Earth

24. Sun’s Energy • Fusion reaction – when to atoms are fused into one

25. Depend on Sun

27. Sun’s layers • energy created in the core moves outward through the radiation zone and convection zone into the Sun’s atmosphere. How is energy created in core?

28. Sun’s Atmosphere • Photosphere: lowest layer gives off light and is about 6,000 K. (10,340.33 °F) • “surface”

29. Sun’s Atmosphere • Chromosphere: above photosphere, extends 2,000 km above photosphere

30. Sun’s Atmosphere • Corona – extends (millions of km) into space, the 2 million K (3,599,540.33 °F) • releases charged particles as solar wind.

31. Surface Features • sunspots: dark areas cooler than their surroundings. • Temporary features which come and go over days, weeks, or months • Increase and decrease in a 10 to 11 year pattern called solar activity cycle.

32. Sun’s rotation • Studying sunspots showed the Sun has differential rotation • faster at equator – 25 days • Slower at poles – 35 days

33. Sun’s Surface Features • Prominences: huge, arching gas columns possibly caused by magnetic fields

34. Solar flares: Violent eruptions near sunspots

35. Coronal Mass Ejections (CMEs): When large amounts of electrically – charged particles are ejected form the corona 2-3 times a day

36. Highly charged solar wind particles can disrupt radio signals, damage satellites that orbit Earth.

37. Near Earth’s polar areas solar wind material can create light called an aurora.

39. Middle-aged / average star • Typical absolute magnitude with yellow light. • Takes 8 min. to get here • Unusual: Sun is not part of a multiple star system or cluster (only 1 star near us!)

40. Star Systems • Binary System – two stars orbit each other • Triple Star System – when 3 stars orbit each other • Star Cluster – many stars relatively close to each other, gravity is strong

41. Evolution of StarsSection 3

42. Hertzsprung – Russell DiagramH-R diagram • higher temperatures = brighter absolute magnitude • Main sequence – group of stars running diagonally across diagram; most stars fit into this band (90%) • Hot, blue, bright in upper left • Cool, red, dim stars in the lower right • Yellow like our sun is in between

43. Most stars are small, red stars found in the low right

44. White dwarfs – hot but not bright • Located in lower left corner of H-R diagram • Same size as Earth • Giants or red giants – bright but not hot • Located in upper right corner of H-R diagram • Supergiants – bright but not hot • Located in upper right of H-R diagram

45. White dwarf

46. Giants and Red Giants Red giant Mira Red Giant Mira and its companion When two stars orbit each other it is called?

47. Supergiant

48. How do stars shine? • Same as Sun NUCLEAR FUSION • Energy given off as visible, infrared, and UV light • Only small amounts make it to Earth

49. E=MC² • Albert Einstein • Mass can be converted into energy • E = energy • M = mass • C = speed of light • Small amounts of mass “lost” during fusion can be converted into large amounts of energy

50. Fusion in core • 2 H nuclei collide • 1 proton decays to neutron energy • 1 more proton fuses to He energy • Another He isotope combines with the other and fuse • Helium nucleus forms 2 protons break away energy