Early Greeks saw it as a Titan god called Helios, who
daily drove a chariot across the sky. The Romans
called it Sol.
Helios lived in the east and emerged each dawn,
driving a chariot drawn by four fiery winged horses. He
was crowned with the aureole of the Sun. Homer
describes him as giving light to both gods and men.
Sol was the Latin incarnation of Helios. Sol drove his
chariot, which carried the sun, across the sky every day.
He was important to farming and crops.
An almost perfect sphere, the Sun is one of more than
100 billion stars in our galaxy, the Milky Way.
I have lived most of my life in the Southwest, with its big
skies and brilliant sunshine. When I was in school, our
science teacher called the Sun and other stars a mass
of burning gas, a designation that stuck with me
because of the rhyme.
The Sun is a yellow dwarf star, in the top 10% of stars
by mass. The outer layer of the sun is roughly 10,000
degrees F, while core temperatures reach more than
27 million. The energy it produces is the equivalent of
100 billion tons of dynamite a second.
It was born some 4.6 billion years ago from a giant,
rotating cloud of gas and dust known as the solar
nebula. As the nebula collapsed, it spun faster, flattening
into a disk.
After about 5 billion years, the sun, like any other star will
swell to become a red giant, engulfing Mercury, Venus and
Earth. It will then collapse, becoming a white dwarf.
The Sun does not have a solid surface, but is held together
by its own gravity. Since it is not solid, different parts of it
rotate at different rates. At the equator, it spins about once
every 25 days, but at its poles, it spins once every 36 days.
The sun is composed of several layers of different
temperature and density. The hottest and densest section is
that nearest the inner core.
The core represents about 25% of the Sun's radius and has
a temperature of some 10,000,000 Kelvin and a pressure of
250 billion atmospheres.
The radiative zone, which extends out to about 70% of the
Sun's radius, is some 8,000,000 K. And the convection zone,
including most of the rest of the Sun, is about 500,000 K.
The solar atmosphere is made of up the photosphere, the
chromosphere and the corona, the outermost layer, which is
unstable in shape and includes coronal loops and solar
The Sun's power is produced by nuclear fusion reactions.
Each second about 700,000,000 tons of hydrogen are
converted into helium and gamma rays. As it travels toward
the surface, its temperature lowers until it is primarily visible
light. The final 20% of the way, the energy is carried more by
convection than by radiation.
The surface of the Sun, or photosphere is about 5800 K.
Sunspots are cooler, only 3800 K, and can be as large as
50,000 km in diameter.
The corona is only visible in a solar eclipse, when the Moon
comes directly between the Earth and the Sun.
The following pages of this site give more details on the
Solar System, the process of photosynthesis by which the
Sun's energy is converted to food, and other ways the Sun is
essential to life.
If you have a response to this website or thoughts about the
Sun you'd like to share, please write me at b.silvey
@sbcglobal.net. Have a sunny day!
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