1. Red Stars, Blue Stars, Old Stars, New Stars Session 1 Julie Lutz University of Washington

2. Orion: A Bunch of Stars Greek: Hunter Japanese: A water drum Brightest Stars: Betelgeuse, Rigel Orion Nebula: The Smoking Star

3. Orion: A Deeper View

7. Session 1: Basic Properties of Stars Imagine that you are an astronomer who undertakes studies of stars. What sorts of things would you like to know about them?

8. Some Properties of Stars Temperature What makes them shine? Energy source? Chemical composition Are they moving? If so, how? Do they change (timescale)? Distance from solar system Apparent brightness in the night sky “True” brightness or luminosity Diameter (assuming round)

9. Astronomer’s Toolkit Principles of physics, chemistry, math Telescopes and auxiliary instruments Computers for data collection and analysis

13. Some Solar Properties About 93 million miles from Earth 109x diameter Earth 330,000x as massive as Earth Surface temperature 10,000F

14. Distances to Nearby Stars Use “parallax”--small shifts in star position due to Earth moving around sun Unit: parsec 1 parsec=206265 astronomical units

15. Units for Star Distance Parsec (pc) Light Year (ly)=distance that a light beam would travel in one year, about 6 trillion miles Nearest star to sun is 4.26 ly (Proxima Cen)

17. Magnitude Scale First used by Greeks for star catalogs. Smaller numerically the mag, the brighter the star. 1st mag stars are brighter than 5 th mag stars Some objects are brighter than mag 0. Sun is -26.5; full moon is -11; Venus -3.5

18. Apparent Mag, Absolute Mag Apparent mag (m) is the brightness as seen directly in the sky. Goes from -26.5 to +28 Absolute mag (M) is a measure of the TRUE brightnesses (luminosities) of objects relative to each other. Particularly useful for comparing stars.

19. Definition of Absolute Mag Brightness that a star would have if it were at a distance of 10 pc. 10 pc was an arbitrary choice Idea is to line ‘em up and compare brightness at some standard distance. M, m and distance are related

20. Mizar in Ursa Major m=2.2 M=0.3 Distance=24 parsecs or 78 light years

21. Rigel in Orion M=0.2 M=-6.7 Distance=240 parsecs or 800 light years

22. The Sun m=-26.5 M=4.5 Distance=0.000005 pc or 0.000018 ly IF the Sun were 10 pc away, it would have a brightness like the Pleiades stars

23. Luminosity Luminosity is a “physics term” for the true brightness of a star, so L is related to absolute magnitude Some stars are many times more luminous than the sun, others much less

24. Star Color Indicates Surface Temperature

25. Star Card Activity

26. Information Gathering Observe many stars to find their temperatures and luminosities. Make a graph of this information Called a Hertzsprung- Russell (HR) Diagram

30. What We Know So Far Stars seem to have particular patterns in a diagram of Temp vs Luminosity Most stars are on the “Main Sequence” A few are giants (10s x solar diameter), supergiants (100s x solar diameter), white dwarfs (planet-sized) What does this mean? Need more info!

31. How About Finding the Masses of Stars? Use principles of gravitational attraction. Binary stars--2 stars in orbit Different types of binary systems

32. Binary Star

33. Eclipsing Binary

35. Stellar Masses Range from about 0.07 to 120 times mass of sun On the Main Sequence, most massive stars are in upper left (blue), least in lower right

37. How did astronomers figure out the patterns of stellar evolution? HR Diagram Thermonuclear reactions Star masses and sizes Star clusters Nebulae--gas and dust

38. Summary of Session 1 Most stars have temps between 3000 K and 30,000 K. Stars have wide range in luminosity. Some are 10s of 1000s of times more luminous than sun; others much less luminous. Masses range from 0.07 to 120 times mass of sun Diameters planet-sized to 100s x sun

40. Some Properties of Stars Temperature What makes them shine? Energy source? Chemical composition Are they moving? If so, how? Do they change (timescale)? Distance from solar system Apparent brightness in the night sky “True” brightness or luminosity Diameter (assuming round)