ASTR 3 Lecture Notes - Lecture 18: Radial Velocity, Semi-Major And Semi-Minor Axes, Main Sequence
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Magnitudes: an inverted scale. brighter objects have a smaller magnitude. Eyes work at a logarithmic scale: changes magnitude by 5, and the brightness by 100: temperature: Use the w(cid:28637)(cid:28633)(cid:28642)"(cid:28647) law (cid:28648)(cid:28643) (cid:28637)(cid:28632)(cid:28633)(cid:28642)(cid:28648)(cid:28637)(cid:28634)y (cid:28648)(cid:28636)(cid:28633) (cid:28648)(cid:28633)(cid:28641)(cid:28644)(cid:28633)(cid:28646)a(cid:28648)(cid:28649)(cid:28646)(cid:28633). The original classification: based on the strength of hydrogen absorption lines. O stars are the hottest, and m stars are the coldest. Almost most of them are hydrogen and helium. In the near 20 years, two colder and new kinds of stars are discovered: l, t: size and linear radius: Luminosity is proportional to the radius2 * temarature4(blackbody law! Supergiant: more than 100 times of the sun: mass. P2=a3/mtotal: astrometric binaries: two stars can be seen orbiting each other. So we measure the orbit period and the semi-major axis: spectroscopic binaries: too small to directly observe, but we see the lines in the spectra moving---doppler effect. Radial velocity: the velocity of a star moving toward or away from us.
