The Celestial Sphere

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spectrum of Sun
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stellar spectra
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• The Hertzsprung-Russel diagram
• a.k.a. HR diagram
• Vertical axis L
• Horiz. axis Ts

color of the star
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cartoon showing current idea for how a star
forms
(b) the center of a core collapses (due to its
gravity) to form proto-star and disk (d) After
clearing protostar and proto-planetary disk
(a) denser cores form in dense molecular
clouds (c) outflows shoot out of poles of the
star/disk system
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stage c (almost d) a protostar with disk and jet
infrared image
optical image
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stage a a dense molecular cloud core