Science of the Sun
The story of our solar system begins with a very large star, not
our Sun. Huge stars go through their lifecycles quickly, so this
large star went through its lifetime rapidly and exploded as a
supernova. The supernova explosion left behind a huge cloud, or
nebula, of gas and dust. This nebula was made up mostly of hydrogen
and helium, but it also included heavy elements, like gold, which
can only be formed in a supernova explosion. Eventually the nebula
began to collapse under its own weight. The nebula already would
had had a slight rotation left over from the explosion that formed
it. As it collapsed, it started spinning faster and faster in
order to conserve angular momentum, like a figure skater increases
her spin by pulling in her arms. This spinning causes the cloud
to flatten into a disk. Some of the hydrogen and helium began
to clump in the center, forming the protosun.
rho Ophiuchi as observed by the Infrared
Space Observatory
This is a star-forming nebula. Very
bright newborn are hidden among the clouds of the nebula.
The protosun was surrounded by tiny clumps of dust and other gases.
Sometimes these
clumps would stick together when they collided. In about 10,000
years, these clumps
would build up into planetesimals up to about a hundred miles
across. Over tens of
millions of years, the planetesimals combined to form protoplanets
that became the solar
system we have today. The protoplanets were larger than the planets
they eventually
became because they had not yet contracted, which gravity would
later force them to do.
Some of large planetesimals may have become moons, but most moons
formed around
their planets in a minature version of the process that formed
the rest of the solar system.
The protosun continued to collapse under its own weight. Eventually
the pressure was so
high at its center that temperatures were produced high enough
to trigger nuclear fusion.
Hydrogen atoms were combined to form helium, releasing energy
in the process.
Why are the inner planets small and rocky while the outer ones
are huge balls of gas?
Often very young stars are unstable and will flare with huge stellar
winds. These flares
from the young Sun may have blown off the outer gassy layers of
the inner planets.
The Sun
In addition to giving us the warmth that makes life possible on
Earth, the Sun offers us an
opportunity to study a star up close. The Sun is a very medium
star- medium-sized,
medium temperature, and middle-aged.
Anatomy of the Sun
Core: this the part of the Sun where nuclear fusion actually takes
place. The core’s
diameter is only about 10 percent that of the entire Sun and temperatures
there reach into
the tens of millions of degrees.
Radiative zone: the radiative zone is the region where heat from
the core travels directly
by radiation, like the burner on a stove heats up the bottom of
a pan.
Convection zone: here heat is carried by convection- the material
in the zone is physically
moving and carrying the heat with it. This is like a pot of boiling
oatmeal. The hot
oatmeal at the bottom of the pot rises while the cool oatmeal
at the top falls.
Photosphere: the photosphere is the lowest region of the solar
atmosphere. The
photosphere is very tenuous and makes up only a small amount
of the total mass of the
Sun. However, it is this layer of the Sun that produces the light
that we see.
Chromosphere: The chromosphere is a shell of small spikes called
spicules that look like
flames. Spicules are columns of gas that rise from the surface
of the Sun, a few hundred
miles across and several thousand miles tall.
Corona: The corona is the outermost layer of the Sun and extends
past the orbits of all the
planets. The edge of the corona is called the heliopause. Voyager
1 recently crossed the
heliopause and officially left the soalr system. The corona is
very tenuous and can only
be observed during a total solar eclipse, when the Moon covers
the photosphere. The
corona is extremely hot, over 2 million degrees, while the photosphere’s
temperature is
only about 6,000 degrees. The reason why the corona is so hot
is still a mystery and is
studied both during total solar eclipses and by special telescopes
called coronagraphs
which block out the photosphere the same way the Moon does.