ASTR 1102 Lecture : Lecture15
Document Summary
Doppler effect - too small to visibly affect color. Distant galaxies do appear red because of the doppler effect. No stars in our own galaxy are moving fast enough for that. Putting it all together: the hertzsprung russell diagram. Mnemonic oh be a fine girl/guy, kiss me". Stellar absorption lines can be used to measure temperature as well as chemical composition. Cool transparent gas in front of hot gas produces absorption lines. Top of stellar photosphere is cooler than the lower layers. In hot gas atoms move faster and collide. Helium with all electrons is hei, with one missing is heii. Higher gravity star is more compact. More compact star smaller radius and lower luminosity. M2 iab very low gravity, large radius, supergiant (ia or ib) We can determine spectral and luminosity class. Place star in h-r diagram and determine luminosity. Not as precise as (geometric) parallax, but better than nothing. Only option in much of the galaxy.
