From Wikipedia, the free encyclopedia
The Sun (Latin:
Sol) is the star at the center of the Solar System. The Earth and other matter (including other planets,
comets and dust)
orbit the Sun, which by itself accounts for about 99.8% of the solar system's mass.
Energy from the Sun, in the form of sunlight, supports almost
all life on Earth via
photosynthesis, and drives the Earth's climate and weather.
The Sun is composed of
hydrogen (about 74% of its mass, or 92% of its volume), helium (about 25% of mass, 7% of volume), and trace quantities
of other elements. The Sun has a spectral class of G2V. G2 implies
that it has a surface temperature of approximately 5,780 K, giving it a white color which, because of atmospheric
appears yellow as seen from the surface of the Earth. This is a subtractive effect,
preferential scattering of blue photons (causing the sky color) removes
enough blue light to leave a residual reddishness that is perceived as yellow. (When
low enough in the sky, the Sun appears orange or red, due to this scattering.)
Its spectrum contains
lines of ionized and neutral metals as well as very weak hydrogen lines.
The V (Roman
five) suffix indicates that the Sun, like most stars, is a main sequence star. This means that it generates
its energy by
nuclear fusion of
hydrogen nuclei into
helium and is in a state of hydrostatic equilibrium, neither
contracting nor expanding over time. There are more than 100 million G2 class stars
in our galaxy. Because of logarithmic size distribution, the Sun is actually brighter
than 85% of the stars in the
galaxy, most of which are
The Sun orbits the center of the Milky Way
galaxy at a distance of approximately 26,000 light-years from the galactic center, completing one revolution
in about 225–250 million years. The orbital speed is 217 km/s, equivalent to one light-year
every 1,400 years, and one AU every 8 days.
It is currently traveling through the Local Interstellar Cloud in the low-density
zone of diffuse high-temperature gas, in the inner rim of the Orion Arm of the Milky Way Galaxy, between the larger Perseus and Sagittarius arms of the galaxy. Of the
stellar systems within 17 light years from the Earth, the sun ranks 4th
absolute magnitude as a fourth magnitude star (M=4.83).