# Sun

 Mass (Earth=1) 33,280 Mean diameter (10^6 m) 1392 Rotation period 26-37 d Mean distance to Earth, 10^6 km 149 Density (water=1) 1.41 Surface gravity m/s^2 274

Earth's Sun is a medium-sized star which lies on the main sequence with 90% of the known stars. It has a surface temperature of 5800 K, putting it in spectral class G2. Its mass is 1.989 x 10^30 kg and its mean radius is 6.96 x 10^8 meters.

The sun radiates energy at the rate of 3.90 x10^ 26 watts. Just outside the earth's atmosphere solar energy is received, assuming normal incidence, at the rate of 1340 watts per square meter.

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.

The composition of the sun is 74% hydrogen, 25% helium and 1% 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 37 days at the poles but 26 days at the equator

Its apparent magnitude is -26.8 and its absolute magnitude is +4.8 .

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.

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