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1. Stellar parallax is used to measure the

Chap. 17 - Warm-up 2-11-13. 1. Stellar parallax is used to measure the. a) sizes of stars. c) temperatures of stars. b) distances of stars. 2. You can best model the size and distance relationship of our Sun & the next nearest star using.

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1. Stellar parallax is used to measure the

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  1. Chap. 17 - Warm-up 2-11-13 1. Stellar parallax is used to measure the a) sizes of stars. c) temperatures of stars. b) distances of stars. 2. You can best model the size and distance relationship of our Sun & the next nearest star using a) two beach balls separated by 100 city blocks. b) two golf balls 100 km apart. c) two baseballs 100 yards apart. The Sun is about one million miles in diameter. The next nearest star is about 25 million times farther away.

  2. Chap. 17 - Warm-up 2-12-13 3. In the stellar magnitude system invented by Hipparchus, a smaller magnitude indicates a _____ star. a) brighter b) hotter c) cooler d) fainter 4. A star’s apparent magnitude is a number used to describe how our eyes measure its a) distance. b) temperature. c) brightness. d) absolute luminosity. http://www.youtube.com/watch?v=y_Q4VGvexPA

  3. Chap. 17 - Warm-up 2-13-13 5. The star's color index is a quick way of determining its: A) density B) luminosity C) temperature D) mass 6. What physical property of a star does the spectral type measure? A) density B) luminosity C) temperature D) mass

  4. Chap. 17 - Warm-up 2-26-13 7. At the distance of Jupiter (6 times further away from the Sun than Earth) the amount of sunlight received per square centimeter different by what factor? A) 6 times less B) 12 times lessC) 36 times less D) 6 times more

  5. Chap. 17 - Warm-up 2-28-13 What is a parsec? parsec - distance at which a star must lie in order for its measured parallax to be exactly 1 arc second. _ 1 parsec (pc) ~ 206,000 AU _ 1 parsec (pc) ~ 3.3 light yrs 1 _______________ distance (pc) = parallax (arc sec.) COPY THIS INTO NOTES/WARM-UPS http://www.youtube.com/watch?v=nrIfifz9bjY http://www.youtube.com/watch?v=6zV3JEjLoyEhttp://www.youtube.com/watch?v=SqI67fkdiL8

  6. Chap. 17 - Warm-up 2-28-13 What is a parsec? parsec - distance at which a star must lie in order for its measured parallax to be exactly 1 arc second. _ 1 parsec (pc) ~ 206,000 AU _ 1 parsec (pc) ~ 3.3 light yrs 1 _______________ distance (pc) = parallax (arc sec.) COPY THIS INTO NOTES/WARM-UPS http://www.youtube.com/watch?v=nrIfifz9bjY http://www.youtube.com/watch?v=6zV3JEjLoyEhttp://www.youtube.com/watch?v=SqI67fkdiL8

  7. Chap. 17 - Warm-up 3-1-13 8. The absolute magnitude of a star is its brightness as seen from a distance of: A) one AU. B) one light year. C) ten parsecs. Absolute magnitude is simply apparent magnitude at a distance of 10 pc 9. If a star is found to be about 100 parsecs distant, its parallax is: http://www.youtube.com/watch?v=72oJzVVcEzc

  8. 1 _______________ distance (pc) = parallax (arc sec.) Ex: If a star is found to be about 100 parsecs distant, its parallax is: 1 _______________ distance (pc) = parallax (arc sec.) 1 ___________ parallax (arc sec.) = distance (pc) 1 ___________ parallax (arc sec.) = 100 (pc) parallax (arc sec.) = 0.01 (arc sec.)

  9. Chap. 17 - Warm-up 3-6-13 10. Stars that have masses similar to the Sun's, and sizes similar to the Earth are A) main sequence stars. B) white dwarfs. C) red giants. D) brown dwarfs. 11. On the H-R diagram, the Sun lies A) at the top left. B) at the bottom left. C) at the bottom right. D) about the middle of the main sequence.

  10. 17.1 The Solar Neighborhood Nearest star to the Sun: Proxima Centauri, which is a member of the three-star system Alpha Centauri complex Model of distances: Sun is a marble, Earth is a grain of sand orbiting 1 m away Nearest star is another marble 270 km away Solar system extends about 50 m from Sun; rest of distance to nearest star is basically empty

  11. 17.2 Luminosity and Apparent Brightness Luminosity, or absolute brightness, is a measure of the total power radiated by a star. Apparent brightness is how bright a star appears when viewed from Earth; it depends on the absolute brightness but also on the distance of the star.

  12. Do this on your own A star lies about 13 light years distant, thus its parallax is about: 1 ___________ parallax (arc sec.) = distance (pc) First, change units from light yrs to pc 1 pc __________ 13 light yrs x = 3.94 pc ~ 4 pc 3.3 light yrs 1 ______ = 0.25 (arc sec.) parallax (arc sec.) = 4 (pc) 1 parsec (pc) ~ 3.3 light yrs

  13. Another parsec example If a star has a parallax of 0.05", then its distance in light years is about: 1 _______________ distance (pc) = parallax (arc sec.) 1 _______________ distance (pc) = 0.05 (arc sec.) 3.3 light yrs __________ distance = 20 pc x = 66 light yrs 1 (pc) 1 parsec (pc) ~ 3.3 light yrs

  14. Copy into notes. FamiliarExamples Oh Be A Fine Girl Kiss Me Mintaka (O9) Rigel (B8)Sirius (A1)Canopus (F0)Sun (G2)Aldebaron (K5)Betelgeuse (M2)

  15. Copy this: STAR SIZES

  16. 17.5 The Hertzsprung–Russell Diagram The H–R diagram plots stellar luminosity against surface temperature. This is an H–R diagram of a few prominent stars.

  17. 17.5 The Hertzsprung–Russell Diagram Once many stars are plotted on an H–R diagram, a pattern begins to form. These are the 80 closest stars to us; note the dashed lines of constant radius. The darkened curve is called the main sequence, as this is where most stars are. Also indicated is the white dwarf region; these stars are hot but not very luminous, as they are quite small. http://www.youtube.com/watch?v=mcPrSAKNeMI

  18. 17.5 The Hertzsprung–Russell Diagram An H–R diagram of the 100 brightest stars looks quite different. These stars are all more luminous than the Sun. Two new categories appear here—the red giants and the blue giants. Clearly, the brightest stars in the sky appear bright because of their enormous luminosities, not their proximity.

  19. 17.5 The Hertzsprung–Russell Diagram This is an H–R plot of about 20,000 stars. The main sequence is clear, as is the red giant region. About 90% of stars lie on the main sequence; 9% are red giants and 1% are white dwarfs.

  20. 17.7 Stellar Masses Many stars are in binary pairs; measurement of their orbital motion allows determination of the masses of the stars.

  21. 17.7 Stellar Masses Spectroscopic binaries can be measured using their Doppler shifts

  22. 17.7 Stellar Masses Finally, eclipsing binaries can be measured using the changes in luminosity

  23. 17.7 Stellar Masses Mass is the main determinant of where a star will be on the main sequence

  24. More Precisely 17-3: Measuring Stellar Massesin Binary Stars In order to measure stellar masses in a binary star, the period and semimajor axis of the orbit must be measured. Once this is done, Kepler’s third law gives the sum of the masses of the two stars. Then the relative speeds of the two stars can be measured using the Doppler effect; the speed will be inversely proportional to the mass. This allows us to calculate the mass of each star.

  25. 17.8 Mass and Other Stellar Properties This pie chart shows the distribution of stellar masses. The more massive stars are much rarer than the least massive.

  26. 17.8 Mass and Other Stellar Properties Mass is correlated with radius and is very strongly correlated with luminosity

  27. 17.8 Mass and Other Stellar Properties So the most massive stars have the shortest lifetimes—they have a lot of fuel but burn it at a very rapid pace. On the other hand, small red dwarfs burn their fuel extremely slowly and can have lifetimes of a trillion years or more.

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