The sun is situated at the center of the solar system, where
it is by far the biggest object. It keeps 99.8 percent of the solar system's
mass and is around 109 times the size of the Earth, about one million Earths
could fit inside the sun.
The visible part of the sun is approximately 10,000 degrees
Fahrenheit (5,500 degrees Celsius), while temperatures within the core reach
greater than 27 million F (15 million C), driven by nuclear reactions. One
would need to explode 100 billion tons of dynamite every second to match the
energy made by the sun, based on NASA.
The sun is greater than 100 billion stars in the Milky Way.
It orbits some 25,000 light-years through the galactic core, finishing a
revolution once every 250 million years or so. The sun is fairly young, part of
a generation of stars called Population I, which are fairly rich in elements
weightier than helium. An older generation of stars is known as Population II
and an earlier generation of Population III may have existed, even though no
members of this generation are known yet.
Formation & Evolution
The sun was formed about 4.6 billion years back. Many
scientists believe the sun and the remaining solar system created from a giant,
rotating cloud of dust and gas called the solar nebula. As the nebula collapsed
due to its gravity, it spun quicker and flattened into a disk. Most of the
material was drawn toward the center to make the sun.
The sun has sufficient nuclear fuel to remain much as it is
now for another 5 billion years. After that, it will swell to become a red
giant. At some point, it will shed its outer layers and the rest of the core
will collapse to turn into a white dwarf. Slowly, this will fade, to enter its
last phase as a dim, cool theoretical object occasionally known as a black
Internal Structure and Atmosphere
The sun and its atmosphere are split into a number of zones
and layers. The solar internal, from the inside out, is comprised of the core,
radiative zone and the convective zone. The solar atmosphere above that
contains the chromosphere, photosphere, a transition region and the corona.
Beyond that is the solar wind, an outflow of gas through the corona.
The core extends through the sun's center to about a quarter
of the way to its surface. Even though it only comprises roughly 2 percent of
the sun's volume, it is almost 15 times the density of lead and holds almost
half of the sun's mass. Next is the radiative zone, which extends through the
core to 70 % of the way to the sun's surface, making up 32 percent of the sun's
volume and 48 percent of its mass. Light through the core become scattered in
this zone, so that an individual photon often may take a million years to go
The convection zone reaches approximately the sun's surface
and comprises 66 percent of the sun's volume however only a little more than 2
percent of its mass. Roiling convection cells of gas dominate this zone. Two
main types of solar convection cells exist, supergranulation cells about 20,000
miles (30,000 kilometers) in diameter and granulation cells about 600 miles
(1,000 kilometers) wide.
The photosphere is actually the lowest layer of the sun's
atmosphere and gives off the light we see. It is approximately 300 miles (500
km) thick, even though most of the light arises from its lowest third.
Temperatures within the photosphere vary from 11,000 F (6,125 C) at base to
7,460 F (4,125 C) at top. Next up is the chromosphere, which is hotter, as much
as 35,500 F (19,725 C) and is apparently composed entirely of spiky structures
called spicules typically some 600 miles (1,000 km) across and approximately
6,000 miles (10,000 km) high.
Next is the transition area a few hundred to
several thousand miles or kilometers thick, which is warmed up by the corona
above it and sheds most of its light as uv rays. At the top is the super-hot
corona, which is made from structures including loops and streams of ionized
gas. The corona generally ranges from 900,000 F (500,000 C) to 10.8 million F
(6 million C) and can even reach tens of millions of degrees when a solar flare
happens. Matter from the corona is blown off as the solar wind.