Although we refer to the photosphere as a layer of the Sun, in actuality it is a part of the Sun's atmosphere. It is a very thin layer in comparison with the rest of the Sun, and is the only part of the Sun that we can actually see when looking at it from Earth, because the photosphere is where the light is emitted. (But of course you should never look straight at the Sun!) The light that we see coming from the Sun is actually far from its real intensity because the photosphere's opaqueness absorbs much of it. So the place that creates the light, absorbs it as well!
Looking at different places on the Sun changes where the visible light comes from. When looking at the center of the disk, the light that we see comes from the base of the photosphere. But as we look closer to the limb, the light comes from higher up, so at the very edge of the Sun, it is emerging from a spot far above the base of the photosphere. This makes the Sun look less bright and slightly redder on the limb, and brighter on the disk.
In the photosphere, granulation, supergranulation, faculae, and sunspots are seen.
These are seen as dark spots in the photosphere that have extremely high magnetic fields. They usually show up in groups of two sets, where one set has a north magnetic field and the other set has a south magnetic field. They have a lower temperature than their surroundings, which gives them this darkened appearance in white light. To the right is a very close-up image of a sunspot.
These are seen on the Sun near the limb. Instead of appearing dark like sunspots, they show up as bright spots on the photosphere. This is because they are hotter than their surroundings. They are magnetic also, but their magnetism is more concentrated than that of sunspots. You can see the faculae as bright spots in the images to the right.
Granules are related to the convective zone. The granulation that shows up in the photosphere is a result of the rising and falling of hot gas that takes place in the convective zone. The bubbles seen are the material that reaches the top of the convective zone--the photosphere. (For a better understanding and an image of granulation, check out the page on the convective zone.)
Supergranules are just larger version of granules. They have magnetic field "bunches" that flow within them. Supergranules look similar to granules, except that they are 35,000 kilometers across as opposed to 1,000 kilometers across.
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