Temperature

Blackbody Radiation Heated gas radiates electromagnetic energy, called blackbody radiation. Higher temperatures create higher energies. Cooler stars red Hotter stars blue low energy high energy frequency intensity

Measuring Temperature Measure the star’s spectrum. Measure the wavelength with the peak intensity. Convert the wavelength to a temperature. Measure the intensity of the star with a red filter. Measure again with a green filter, then a blue filter. Match to the right temperature profile. peak wavelength

Absorption Lines Ionized gases at a star’s surface absorb specific frequencies of light. Dark lines in a star’s spectrum Since gases ionize at different temperatures, the lines tell the temperature of the star.

Spectral Types The types of spectra were originally classified only by hydrogen absorption, labeled A, B, C, …, P. Eventually arranged by temperature. O, B, A, F, G, K, M Our Brother Andy Found Green Killer Martians Type Temperature O 35,000 K B 20,000 K A 10,000 K F 7,000 K G 6,000 K K 4,000 K M 3,000 K

Spectral Classes Some bright stars class Sun G2 Sirius A1 Alpha Centauri G2 Vega A0 Capella G8 Rigel B8 Betelgeuse M1 Aldebaran K5 Each type is split into 10 classes from 0 (hot) to 9 (cool). Temperature and luminosity are not the same thing.