Basic Astronomy

Stars


Stars

Stars are massive bodies bounded by gravity. Our own Sun is closest star from us. It is mainly formed of plasma. Fission and fusion are main source of energy in stars. When most of the fuel of a star is finished, the star collapses due to huge gravitational pull. It often result a supernova blast at the time of the collapse and most of the matter of the star exploded away in the space. Depending on the mass of the remaining element after supernova explosion, the star become either white dwarf, neutron star or black hole.

Spectral Clarification of Stars

Stars are classified by their temperature and spectra (elements that they emit or absorb). There are seven main types of stars. In order of decreasing temperature, the classes of stars are O, B, A, F, G, K, and M.

Spectral Clarification of Stars

Star TypeColorApproximate Surface TemperatureAverage Mass
(The Sun = 1)
Average Radius
(The Sun = 1)
Average Luminosity
(The Sun = 1)
Main CharacteristicsExamples
OBlueover 25,000 K60151,400,000Strong UV continuum. Singly ionized helium lines (H I) either in emission or absorption. 10 Lacertra
BBlue11,000 - 25,000 K18720,000Neutral helium lines (H II) in absorption.Spica
ABlue7,500 - 11,000 K3.22.580Hydrogen (H) lines strongest for A0 stars, decreasing for other A's.Vega, Sirius
FBlue to White6,000 - 7,500 K1.71.36Metallic lines are noticeable. Ca II absorption visible. Procyon
GWhite to Yellow5,000 - 6,000 K1.11.11.2Absorption lines of neutral metallic atoms and ions (e.g. once-ionized calcium).Sun
KOrange to Red3,500 - 5,000 K0.80.90.4Metallic lines, some blue continuum.Aldebaran
MRedunder 3,500 K0.30.40.04
(very faint)
Some molecular bands of titanium oxide.Betelgeuse





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