I did a Google search on this topic and found the
Look to Stan Odenwald's
"Ask the Astronomer" for this one.
The Astronomy Cafe
are sunspots dark?
Sunspots are a magnetic
phenomenon on the sun. You can think of them as
small pores on the surface of the sun where lines
of magnetic force enter and exit. Sunspots always
come in pairs like the north and south poles on a
bar magnet. The strength of the sunspot magnetic
fields are usually 1000 times as strong as the
average solar magnetic field. Because magnetic
fields can produce pressure, inside sunspots, the
gas does not need to exert quite as much pressure
as elsewhere on the sun to insure that the total
pressure across a sunspot is in equilibrium with
the gas surrounding the sunspot. Since the cooler
a gas is, the less pressure it exerts, this means
that the gas inside a sunspot can be cooler than
the gas in the rest of the solar surface and
still, with the help of the sunspots magnetic
field, remain in equilibrium.
The average gas
temperature of the solar surface is about 6050 K,
but inside a sunspot, the gas temperature is only
4200 K. The reason a sunspot appears dark is that
the gas inside the spot where the magnetic field
is strongest is only emitting about 1/4 as much
light as from the rest of the solar surface. If
you were to rip a sunspot out from the solar
surface and put it in the night sky, it would
appear as a bright, orange gas, not a dark void.
Click Here to return to the search form.