H.A.L. Astronomy School

1. H.A.L. Astronomy School

2. Star Stuff: Or, Interesting Stuff to Know and Tell about Stars

3. 1930 hours EDT

4. 2030 hours EDT

5. 2130 hours EDT

21. KochabProper Names  Kochab  KocabBayer Designation  Beta Ursae MinorisFlamsteed Number  7 Ursae MinorisBSC  5563HD  131873ConstellationUrsa MinorRight Ascension  14h 50m 42sDeclination  +74° 9' 20“Distance  127 light years  39 parsecsMagnitudeApparent: +2.2Absolute: -0.8 to -0.7Spectral ClassK4OrangeGiantOptimum VisibilityApril/May  Usually visible from  northern latitudes

22. How’s the “seeing”? Using Certain Stars to Determine Limiting Magnitude The 2,3,4, and 5 System:

23. An Illusion of Permanence: At a Casual Glance • Heavens seem eternal and unchanging • Sky we see at night is virtually indistinguishable from the sky seen by our ancestors

24. Empirical Reality, 1 of 3 • Stars are born even NOW from interstellar gas and dust, in cold clouds that are scattered abundantly throughout our galaxy • Perhaps an interstellar cloud encounters one of the galaxy’s spiral arms…

25. Empirical Reality, 2 of 3 • …or perhaps a supernova detonates nearby • From the shock of events like these, the cloud begins to contract under the pull of gravity, forming protostars – the fragments that will one day become stars

26. Empirical Reality, 3 of 3 • As protostar develops, its internal pressure builds and its temperature rises • In time, hydrogen burning can ignite, and a star is born • Clusters of these young stars illuminate the interstellar gas and dust that surround them, producing beautiful glowing nebulae

27. Starbirth, starlife, stardeath • Stars are born, they mature and they grow old • Major stages in their lives can last for millions or even billions of years • Some even blow themselves apart in death throes that enrich interstellar space with the material for future generations of stars

28. Stars Seem Unchanging to Our Eyes But only because of the colossal time scale over which they change

31. The average density of stars in M13 is about 100 times greater than in the neighborhood of the Sun. 150 ly (45 parsecs) Stellar census of a few hundred thousand stars Distance: 23,000 ly (7,000 parsecs)

32. Stellar Astrophysics: The Very Short Course

33. Mass Matters, 1 of 4 • The most massive stars are the most luminous, while the least massive stars are the least luminous • Observation and theory show that there is a lower and an upper mass limit for stars

34. Mass Matters, 2 of 4 • A protostar less massive than 0.08 solar masses can never develop the necessary pressure and temperature to start hydrogen “burning” at its core • Theory indicates this failed star contracts to become a hydrogen-rich object called a brown dwarf

35. Brown Dwarfs • Brown dwarfs are intermediate in their properties between stars and Jovian planets (such as Jupiter with a mass of 0.001 solar masses) • Jupiter is NOT a failed star • Observational confirmation of brown dwarfs did not come until 1994 (Gliese 229)

36. Mass Matters, 3 of 4 • Protostars with masses greater than about 100 solar masses also do not become main-sequence stars • They rapidly become very luminous with pressure so great that it overwhelms the effects of gravity, expelling the outer layers into space and disrupting the star

37. Mass Matters, 4 of 4 • The range for main-sequence stars is between 0.08 and 100 solar masses • High-mass stars are extremely rare • Therefore, stars can range from 8/100 the mass of our Sun to 100 times the mass of our Sun

38. Star Color = Star Temperature O B A F Sun G K M

41. "We are made of star stuff. We are a way that the cosmos can know itself." -----Carl Sagan in the opening sequence of Cosmos