PHYS 206 Stars in General Only 6 of the 20 brightest stars in the sky are closer to us than 10pc  14 of the 20 brightest stars in the sky must have absolute magnitude of at least 1.5 (20 times brighter than the Sun) Out of the 6000 stars visible, only 50 are dimmer than the Sun in absolute magnitude. Question: Is the Sun below average???? Answer: NO!!!!!!!!!!!!! Because, bright stars are very rare, however, when they are bright, they are very bright. Majority of the stars are dim stars, even the closest star to us, Proxima Centauri (+16) is not visible to the naked eye.

PHYS 206 Nearest Stars Only 3 of the 43 nearest stars is among the 20 brightest stars: Sirius, Alpha Centauri, Procyon. 13 out of 44 nearest stars are binaries  total of 59 stars. 43 out of these 59 stars have less than 0.01 L s. Only 3 are as bright as our Sun. If we go to a distance of 10 pc  456 stars. 12 out of these 456 are > 2 L s. 1:20 as bright as the Sun 1:38 as bright as 2 L s. So, the Sun is an average star.

PHYS 206 Near vs. Bright

PHYS 206 Temperature vs. Luminosity

PHYS 206 Hertzsprung-Russell diagram

PHYS 206 Different Stars Main Sequence Stars Giants: Subgiants Giants Supergiants Dwarfs Neutron stars Black holes

PHYS 206 Spectroscopic Parallax The correlation between luminosity and spectral type also gives us further means to measure the distance to far away stars in our galaxy (Spectroscopic parallax)  RUNG 4 Procedure: Determine the star’s spectral type from spectroscopy and measure the star’s apparent brightness. Use the main sequence to get the star’s luminosity. Use the Inverse Square Law for Brightness to get the distance to the star from the apparent luminosity and the absolute luminosity.

PHYS 206 Homework Draw a Hertzsprung-Russell diagram. 1.There are 88 constellations listed in the Appendix 19 of Morrison- Wolff-Fraknoi. 2.Pick two constellations each. 3.Every person should have at least 10 stars in the picked constellations. 4.Using the Internet, find the Color Indices and the Luminosities of these stars. 5.Draw the HR diagram. 6.Groups of 5 should draw all of their data on one paper as well.