NATS 1880 Chapter Notes - Chapter 11: Doppler Spectroscopy, Orbital Eccentricity, Orbital Speed
23 Mar 2017
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Chapter 11: extrasolar planets, their nature and potential habitability. Helium (by mass: the early universe contained only the chemical elements hydrogen and helium. There must be a minimum critical amount of other elements that is necessary for the formation of planets, no one knows the minimum, but the 2% seems sufficient. 8% mass is a minimum because anything below it, the core of the star never becomes hot enough to sustain hydrogen fusion; objects that are star-like but below the minimum mass are known as brown dwarfs. 1) come in different colours which reflect differences in surface temperature. Higher temperature objects emit most of their radiation at shorter wavelengths, so hotter stars are bluer in colour and emit most of their light as uv. Astronomers categorized stars according to a spectral types that corresponds to surface. 2) stars also vary in their brightness (luminosity). High mass stars die in a titanic explosion called supernovae.
