Sun
The orbit of Earth ranges from 1.47 to 1.52 x 10^{11} meters from the Sun. The average light travel time to the earth is 8.3 minutes. The radius of the sun at 696,000 km is 109 times the Earth's radius. Its surface gravity is 274 m/s^{2} or 28.0 times that of the Earth. Its mean density is 1410 kg/m^{3} or 0.255 times the mean density of Earth. The composition of the sun is 71% hydrogen, 27.1% helium and less than 2% of all other elements. The center temperature is modeled to be 15.5 million K. The Sun is fueled by the proton cycle of nuclear fusion. Escape velocity = 618 km/s Period of rotation averages 25.4 days, varying from 34.4 days at the poles to 25.1 days at the equator (Chaisson). Its axis is tilted 7.25° relative to the ecliptic. Its apparent magnitude is 26.8 and its absolute magnitude is +4.8 . Its greatest angular diameter as seen from the Earth is 32.5' . The sun is 7.7 kpc or 25,000 light years from the center of the galaxy and orbits the galaxy in about 200 million years. This corresponds to an orbital velocity of 230 km/s.

Index Solar System Illustration Solar System Concepts Sun Concepts References Chaisson & McMillan Ch 16 de Pater and Lissauer Ch 1  

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