The Sun is our nearest star. Its radiant
energies light up our daytime sky and make all life possible
on this planet, even from as far away as 93 million miles.
Like many things in nature, the Sun consists of many different
parts that influence each other and exchange both energy and
matter.
Energy and Matter
Deep within the Sun's core
where gravitational pressures compress and heat its gases,
atoms collide so furiously that some fuse together. At temperatures
of 15 million degrees Centigrade, its abundant store of
hydrogen turns to helium via thermonuclear fusion. Every
second, 600 million tons of matter are converted to pure,
radiant energy. Some of this energy goes into creating pressure
that literally holds up the Sun against gravity. The rest
leaks out of the dense core in the form of light, and deposits
huge amounts of energy throughout the inside of the star.
It takes many thousands and possibly millions of years for
this light energy to make it to the surface because there
is so much matter in the way.
Like some enormous onion, the Sun's interior
is a collection of regions with unique combinations of temperature,
density and the manner in which energy moves through them.
In a region that astronomers call the radiative zone, light
is the most efficient medium to transport energy from deeper
inside the Sun. The gas moves very little, and rotates in
unison with the rest of the Sun as though it were a solid
substance. While the gas temperatures plummet to only a
few hundred thousand degrees Centigrade, light staggers
to and fro until it gets about 1/3 of the way to the surface.
The outer 1/3 of the Sun convects like a liquid in a boiling
pot, because of a sharp change in the properties of the
gas and its temperature. Astronomers can see these convection
cells on the outer surface of the Sun, called the photosphere,
which is the part that we see from Earth. The small cells
are called granules, but they are in fact nearly as large
as Earth and change their shapes in only a few minutes.
Granules move about on top of larger 'super cells' which
reach deep down into the interior of the Sun within the
convective zone.
Other Stars
Stars much hotter than the Sun,
such as Rigel or Deneb, have no convection zone at all,
while stars much cooler than the Sun, such as Betelgeuse
and Antares, have convective zones that reach almost to
the cores of the stars. Because of the Sun's turbulent surface,
many complex phenomena can occur on the surface as flows
of charged particles cause magnetic fields, and these fields
become entangled and amplified.
Find
out more about the Sun-Earth Connection at the Sun-Earth
Connection Education Forum Web site.
