The sun is the largest
and the most massive object in the solar system, but it is just a medium-sized
star among the hundreds of billions
of stars in the Milky Way
galaxy.
Radius, diameter & circumference
The
sun is nearly a
perfect sphere. Its equatorial diameter and its polar diameter differ by only
6.2 miles (10 km). The mean radius of the sun is 432,450 miles (696,000
kilometers), which makes its diameter about 864,938 miles (1.392 million km).
You could line up 109 Earths across the face of the sun. The sun's
circumference is about 2,713,406 miles (4,366,813 km).
Mass and volume
The
total volume of the sun is 1.4 x 1027 cubic meters. About 1.3
million Earths could fit inside the sun. The mass of the sun is 1.989 x 1030 kilograms,
about 333,000 times the mass of the Earth. The sun contains 99.8 percent of the
mass of the entire solar system, leading astronomers Imke de Pater and Jack J.
Lissauer, authors of the textbook "Planetary Sciences," to refer to
the solar system as "the sun plus some ebris."
Yellow dwarf
It
may be the biggest thing in this neighborhood, but the sun is just average
compared to other stars.Betelgeuse, a red giant, is about 700 times bigger than
the sun and about 14,000 times brighter.
The
sun is classified as a G-type main-sequence star, or G dwarf star, or more
imprecisely, a yellow dwarf. Actually, the sun — like other G-type stars — is
white, but appears yellow through Earth's atmosphere.
Stars
generally get bigger as they grow older. In about 5 billion years, scientists
think the sun will start to use up all of the hydrogen at its center. The sun
will puff up into a red giant and expand past the orbit of the inner planets,
including Earth. The sun's helium will get hot enough to burn into carbon, and
the carbon will combine with the helium to form oxygen. These elements will
collect in the center of the sun. Later, the sun will shed its outer layers, forming
a planetary nebula and leaving behind a dead core of mostly carbon and oxygen —
a very dense and hot white dwarf star, about the size of the Earth.
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