Solar Surface: Definition & Function

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

What is the surface of the Sun made of? What does it look like up close? Learn some key facts about the solar surface, and then test your knowledge with a quiz.

What is the Solar Surface?

The Sun is a constant in all our lives. It provides the daily rhythm of sunrises and sunsets, and it's vital to all life on Earth. The Sun's heat passes through its surface, and in turn heats the surface of the Earth. It provides energy to plants, which are then eaten by animals like us. It keeps the planet warm enough that we don't freeze to death. Without it, we could never survive.

But have you ever wondered what it would be like to stand on the surface of the Sun? Many people have, but the answer would probably be disappointing to most. Perhaps the most obvious problem with a trip to the Sun is the sheer heat it produces. The surface is so hot that anyone who was actually there would be vaporized instantly. And that's not the only reason it would be impossible to stand on the Sun; it's also made up of hot plasma and doesn't really have any kind of solid surface to stand on. So why does it look like it does?

If you've ever seen a blacksmith create a sword or other metal item, you know that it takes a lot of heat to shape metal. You have to put the metal in a fire that's so hot the metal glows. And this is basically the same reason that the Sun glows so bright and appears to have a surface. Even gases and plasmas will glow when heated enough. And the Sun produces a huge amount of heat through a process called nuclear fusion.

Metals glow when hot, and so do gases
Metals glow when hot, and so do gases

Since the Sun isn't solid, that means you can see through layer after layer of plasma. When you look at the Sun, you're not just seeing the outer layer glowing, you're actually seeing light from many layers underneath as well. All these layers combine to produce light so bright that it appears solid.

But the Sun doesn't really have a specific surface. The material that makes up the Sun just gets less and less dense gradually until all you have is empty space. There's no official point where the Sun starts. However, we do have a name for the bright light that appears to be a surface: we call it the photosphere. The photosphere is just the visible apparent surface of the Sun. Light above the photosphere is completely free to exit the Sun without being absorbed first. Light below it can't make it through the layer in one go, making the layer opaque.

The atmosphere of the earth falls off gradually, in the same way as the Sun
The atmosphere of the earth falls off gradually, in the same way as the Sun

Key Facts about the Photosphere

The photosphere appears yellow, but not just a plain yellow. On top of it, you can see features like sunspots, faculae and granules.

Sunspots are dark areas on the surface. They have lower temperatures and usually last for a few days. They're areas where the magnetic field of the Sun is unusually strong. Sunspots are most common during intense solar activity, and that activity can affect the Earth: It can disrupt electronic equipment, and may even affect the climate.

Faculae are bright areas on the surface. They also have a stronger magnetic field, but that field is more focused into a small area than with sunspots.

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