Years ago NASA astronauts went to the moon, which is about , miles away. But that is it. We have not yet visited any other planets or gotten close to the sun. For comparison, the sun is 93,, miles away — much, much further than the moon.
How do scientists determine the layers of the sun? The outer layers, which we can see, are the corona, the chromosphere, and the photosphere. We can use the techniques I described above to measure their temperatures. Inside the sun there are also layers, but we can't see them. We know about them only from detailed mathematical models of the interior of the sun. We test these models to see if they accurately represent how the sun looks and behaves. They give us our best "guess" of what is going on inside the sun.
What is the next closest star to Earth besides our sun? That would be the double star Alpha Centauri. It is the brightest star in the constellation Centaurus, which unfortunately we can't see from the U. Alpha Centauri consists of two stars in orbit around each other. They are nearly twins, and are also very similar to our sun.
It takes 80 years for the two stars to orbit each other. There is a third star, called Proxima Centauri, which may be in orbit around the other two stars. It is a dim, cool star, but happens to lie a little closer to us than the other two. Thus the name Proxima. If there is no oxygen in outer space, how does the sun burn? Don't things need oxygen in order to burn? There is no oxygen in space.
Then how can the sun be burning? The answer to that is that the sun isn't burning the way we usually think of things. The energy and light from the sun come from nuclear reactions deep inside the sun that occur at incredibly high temperatures millions of degrees! That energy keeps the entire sun hot, although at the surface it is ONLY about 10, degrees Fahrenheit. Anything that hot will glow and give off light, and that is why the sun is bright and looks like it is on fire. Why is the sun orange in the morning and bright white in the afternoon?
If you look at the sun when it is first rising in the morning or setting in the evening, it is passing through more of the earth's atmosphere.
The air scatters light, but it scatters blue and green light the most. Why is the sky blue? Because that is all the blue sunlight that the air has scattered! In the middle of the day, the sun seems white because not that much blue light is scattered. But in the morning and evening, most of the blue and green light are scattered. If you take blue and green away from white, you get orange and red.
You may have noticed that the sun seems dimmer in the morning and evening than in the middle of the day. That is correct, because some of the light has been scattered away. Why doesn't the sun look like the other stars? Actually the sun is very much like the other stars.
But it is much closer. The nearest star other than the sun, Alpha Centauri, is over , times farther away! If we put the sun at that distance, it would look just like Alpha Centauri! Is Earth moving away from the sun? No, I don't think Earth is moving away from the sun. It has been in orbit at about the same distance for a long, long time or life would not have survived here.
What is going to happen to the sun? We think that in about 4. The source of the sun's energy and most other stars is nuclear reactions that change hydrogen into helium. Then the center of the star will collapse, but only part way. The outer part will be blown out like a balloon, and our sun will become a "red giant.
At this point, the sun can use nuclear reactions of the helium that it made earlier, and convert it to carbon. When it runs out of nuclear reactions that can occur in the center, the sun will not be able to make much energy.
So it will collapse, but we think that it will become a "white dwarf" — a small but hot star that would be only about the size of the earth! Then the white dwarf will slowly give off its heat, becoming dimmer and cooler, until eventually all that would be left is a star cinder. All this would take many millions of years.
When the sun becomes a red giant, it will be a whole lot hotter in the solar system! It will probably vaporize Mercury, and Venus and Earth would be charred.
The outer planets would probably have their clouds burned away. We think that only really massive, big stars can become black holes. When they get old, they will go through similar although more complex changes.
But when a very massive star collapses, its gravity can be so great that it will compress its mass to a point — a black hole. A black hole still has the same gravity as the star that made it. So it will affect only what is nearby, just like the star, except that if you get too close, zoom down the hole!
But if a star had planets, they could probably continue in their orbits if nothing else changed. And no, the whole galaxy wouldn't be sucked up. We think that there may be big black holes in the center of many galaxies, but they are still not big enough to do that. If the sun is so hot, why doesn't it just burn up? A star can exist because the heat it generates inside, due to nuclear reactions, pushes outward, but this is balanced by its gravity, which pulls inward.
For a star like our sun, these forces are in balance. We think that a really big star, once it uses up all its nuclear fuel, will collapse and nothing can stop it. Gravity will take over, and all the matter in the star will collapse to a point.
Near that point, the gravity is so strong that even light can't escape. Although this may sound pretty crazy, we think we have found black holes at the centers of some galaxies! The sun doesn't burn up because its source of power is nuclear energy.
In the center of the star, there are tremendous temperatures 12 million degrees! Hydrogen is being converted into helium, and energy is given off. The sun has a LOT of hydrogen. We know that the sun is about 4. Why doesn't the sun drift off into another galaxy? Our galaxy is composed of billions of stars. They "hang together" because of their gravity. So our sun is kept in its path in our galaxy by the gravity of all those other stars. Have you seen a picture of a spiral galaxy? We believe that is what the Milky Way looks like.
The sun is in an orbit in our galaxy. It is moving the other stars are too in a huge circle around the center of the galaxy. It takes about million years for it to go around once! If the sun blows up, what effect will it have on the other planets? First, let me assure you that the sun is not going to blow up any time soon!
In about five billion years, the sun will run out of energy. But that is nothing for us to worry about. If the sun became a supernova, the explosion would probably destroy the planets. Fortunately the sun is too small to become a supernova. The next closest star to us is about 4. All of the other stars we can see with our eyes are farther, some even thousands of light-years away.
Stars are found in large groups called galaxies. A galaxy can have millions or billions of stars. The nearest large galaxy to us, Andromeda, is 2. So, we see Andromeda as it was 2. The universe is filled with billions of galaxies, all farther away than this. Some of these galaxies are much farther away. It is That is only million years after the big bang. It is one of the first galaxies ever formed in the universe.
Learning about the very first galaxies that formed after the big bang, like this one, helps us understand what the early universe was like. This picture shows hundreds of very old and distant galaxies. The oldest one found so far in GN-z11 shown in the close up image. The image is a bit blurry because this galaxy is so far away. Oesch Yale University , G. Illingworth University of California, Santa Cruz.
What Is a Light-Year? More to explore What Is a Galaxy?
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