What is the Sun’s
surface made of?
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The full narration of the video.
The Sun has no ground at all. Say you flew a spaceship there to land. What would be under your feet? From far away, the Sun is a bright disk with a crisp edge. It looks like a solid ball.
But up close, the edge disappears. You plunge straight into glowing gas. This gas is about 5,500 degrees, and it's mostly two things: hydrogen and helium. By weight, hydrogen is over seventy percent, helium a quarter, and everything else together is just two percent.
And it's astonishingly thin, far thinner than the air around us, about one ten-thousandth of air at sea level. So how can gas this thin look like a ball with an edge? Think of a foggy day.
From outside, a fog bank looks like a white wall. Walk in, and the wall is gone. You just see less and less. The Sun works the same way. Deeper in, the gas gets thicker and hotter, and light gets blocked and bounced around. It can't get out. Only at this outermost layer can light finally fly straight out.
The surface we see is simply where light starts to escape. Its real name is the photosphere, and it's about five hundred kilometers thick. That sounds thick, but the Sun's radius is seven hundred thousand kilometers.
This layer is one fourteen-hundredth of that, so from Earth, the edge looks as thin as a line. It's so hot here that some atoms lose their electrons. Hot, electrically charged gas like this is called plasma. It's the same stuff glowing in lightning and neon signs.
Through eclipse glasses, the edge of that disk is the photosphere. Never look at the Sun with bare eyes. Look closer, and this layer is anything but calm. Hot gas wells up from below, blob after blob. At the top it cools and dims, then sinks back down at the edges.
The whole surface is tiled with bright cells, each over a thousand kilometers wide, about Beijing to Shanghai. Each cell lasts only a few minutes, then new gas rising up pushes it aside. Back to that spaceship. Past the photosphere, it just falls into thicker, hotter gas, sinking and sinking, with nowhere to stand.
And here's the strange part: the thinner gas above the photosphere is over a million degrees. Why it gets hotter farther out, scientists still haven't fully worked out. Your guess? Magnetic waves carrying heat up, or countless tiny explosions going off?
What if you stood on it?
Is the Sun’s surface solid, liquid, or just a cloud of gas?
The Sun has no ground at all. Stand on it and you just keep sinking.
It is glowing gas all the way down. The deeper you go, the thicker and hotter it gets, and there is never anything to stand on.
That gas is thinner
than air
How hot is 5,500 °C? About as hot as the very center of the Earth.
No ground, so why
a sharp edge?
Think of a foggy day. From far away, fog looks like a wall. Walk into it and the wall is gone; you can only see a small circle around you.
The Sun’s edge works the same way. Deep inside, the gas is so thick that light bounces around and can’t get out. At one layer the gas gets thin enough, and light finally flies straight out, all the way to your eyes.
The layer where light starts to escape is called the photosphere. It is about 500 km thick. That sounds thick, but the Sun’s radius is about 700,000 km, so this layer is only about 1/1,400 of it. From far away, it looks like a sharp line.
One difference: fog only blocks light and doesn’t glow. The Sun’s gas blocks light and glows too.
What’s in
that gas?
By weight, it is about three-quarters hydrogen and one-quarter helium, plus a tiny bit of oxygen, carbon, iron and others.
At this heat, a small share of atoms get knocked loose from their electrons. That makes a gas that carries electricity and glows, called plasma. There is even a formula for how hot it must be for atoms to lose electrons. The same kind of gas glows in lightning and neon signs.
The surface
keeps bubbling
Zoom in on the photosphere and it is covered in cells called “granules”. In the middle of each one, hot gas wells up from below. At the edges it cools, dims and sinks back down, like a pot of boiling porridge.
Each cell is over 1,000 km wide, roughly the distance from Beijing to Shanghai (or New York to Chicago). After a few minutes to about ten, a cell fades and a new one bubbles up.
a million degrees
Your guess: magnetic waves carrying heat up, or countless tiny explosions going off?
Quick check
What is the sharp round edge of the Sun we see?
Like a fog bank: it looks like a wall from afar, but there is no wall. At the Sun’s edge, light just stops getting blocked.
