ay45c3-page32 - Within each spectral class there are ner...

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Unformatted text preview: Within each spectral class there are ner steps: : : : B0, B1, B2,: : :B9, A0, A1: : :A9. etc. B5 is a typical B star. The Sun is a typical G star, that is, G5. When astronomers nally knew the distances to enough stars to get their absolute magnitudes or luminosities, and plotted these against their spectral types or color temperatures, they got a big surprise: (bright) −10 Deneb Rigel Betelgeuse Antares Absolute magnitude or Luminosity −5 0 Mira Arcturus Aldebaran Regulus Vega Sirius A Pollux Procyon A Sun Altair +5 +10 Sirius B +15 Barnard's star Procyon B (dim) O5 B0 (Hot) A0 F0 G0 K0 M0 M8 Spectral Type or Temperature (Cool) The stars are not randomly scattered, but ordered in some weird way! Uh, oh; call in the astrophysicists! This kind of diagram is called a HertzsprungRussell or H-R diagram. Ejnar Hertzsprung discovered it in 1905, and Henry Morris Russell re-discovered it nearly 10 years later. (News travelled slow then. There were very few astronomers in the world and not many international conferences.) 56 ...
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