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The simple answer is that planet sized areas on the sun’s surface are cooler than the rest of the surface and appear darker. Taken away from the brighter background they are still really bright. It’s simply a matter of comparison.
Why they are cooler is a little more complicated. If the simple answer is all you want, great. If not, please read on.
It has to do with stuff called plasma and a thing called magnetism.
Plasma is an atom—in the sun’s case usually an atom of hydrogen or helium-- that has lost electrons because the sun’s intense temperature tears them loose. The loss of electrons leaves the atom with an electrical charge. This is because an electron has a negative charge, so when one or more electrons are torn from an atom the atom is left more positive. The sun’s magnetic field can now influence it. Here’s where the sunspots come in.
In some places the sun’s magnetic field gets twisted--scientists are still trying to figure that one out--and pokes out through the surface, called the photosphere, and arch back in. Under the surface of the sun is an area, called the convection zone, where the hot plasma heated by the sun’s core rises to the surface--like water boiling in a pot. The place where the magnetic field comes out and the place where it in goes back in slows the plasma’s rise to the surface. These places are cooler than adjacent areas where the plasma rises to the surface uninhibited.
The cooler spots look darker because they are cooler and give off less light.
And that is why the sun has spots.
Why they are cooler is a little more complicated. If the simple answer is all you want, great. If not, please read on.
It has to do with stuff called plasma and a thing called magnetism.
Plasma is an atom—in the sun’s case usually an atom of hydrogen or helium-- that has lost electrons because the sun’s intense temperature tears them loose. The loss of electrons leaves the atom with an electrical charge. This is because an electron has a negative charge, so when one or more electrons are torn from an atom the atom is left more positive. The sun’s magnetic field can now influence it. Here’s where the sunspots come in.
In some places the sun’s magnetic field gets twisted--scientists are still trying to figure that one out--and pokes out through the surface, called the photosphere, and arch back in. Under the surface of the sun is an area, called the convection zone, where the hot plasma heated by the sun’s core rises to the surface--like water boiling in a pot. The place where the magnetic field comes out and the place where it in goes back in slows the plasma’s rise to the surface. These places are cooler than adjacent areas where the plasma rises to the surface uninhibited.
The cooler spots look darker because they are cooler and give off less light.
And that is why the sun has spots.
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