Why do stars emit light

The stars with the palest colors are those that, like our Sun, peak in the green. That's because these "green" stars also emit lots of red and blue light. The light combines so it appears white to our eyes. Our definitive article about this is Philip C.

By: Monica Young September 28, By: Maria Temming July 15, Solar System. A view of the Orion nebula, as seen from the Subaru Telescope. The stars behind it can be seen dimly, if at all. Finally light can be pulled aside by gravity. Black holes, which are massive gravitational centers, have gravity so strong that they will pull in light itself and trap it there, keeping it from getting to us.

What is in space besides planets and stars? What is gravity? What is energy? What is frequency? What is wavelength? Did you know that our sun is a star? It's a pretty ordinary, normal kind of star. So that's what a star looks like up close.

Some stars are bigger, some are smaller, some are hotter and look bluish-white and some are cooler and may look yellow, orange, or red. Baby stars are born in big, dark clouds of gas and dust. They start out all wrapped up in these clouds, like blankets protecting them. But there is one thing about baby stars you might not expect. They start out BIG and get smaller as they grow older! That is because the baby stars are formed out of those clouds, and gravity pulls them together to make a star.

The baby star starts out big and cool, surrounded by clouds, so you can't see it. But as it gets older, it gets hotter and brighter.

The clouds are blown away and then you can see the baby star now more like a "toddler". Where do "young" stars get their energy from if nuclear fusion has not yet taken place? When does it finally take place?

Young stars get their energy from gravity. They are slowly contracting, and as they squeeze together that generates energy which gets radiated away as light. Once the center of the star is hot and dense enough millions of degrees! It takes a star the size of our sun about 20 million years to reach this point. Once it starts nuclear fusion, the star can shine for about 10 billion years. The first method is to look at the star's spectrum formed when we spread out the light from the star into the various colors, like a rainbow.

Using special instruments, we can find dark lines in the spectrum that correspond to the elements in a star. The element lithium can be used to get an age for a star because the amount of lithium in a star decreases with time. This is because it gets converted to other elements by nuclear reactions. So if we can measure the amount of lithium in the star, we can get its age the less lithium, the older the star. The second method is to find the age of a cluster, or group, of stars.

Many stars form together in clusters, so they all have the same age. We know from our calculations that very big, massive stars burn up their nuclear fuel very fast and have short lifetimes, while smaller stars use up their fuel much more slowly and can continue giving off light for much longer. By looking at the various stars in the cluster we can see which ones have used up their fuel and become red giants and which ones are still shining as usual.

Then we can figure out that all the stars in the cluster must be the same age as the age of the stars that just recently used up their nuclear fuels. For instance, if all the stars that are greater than three times as massive as our sun have run out of nuclear fuel and have become red giants, then we know that all the stars in the cluster are million years old. Well of course here on Earth we see the sun brighter than anything else! That is because the sun is so much closer than the other stars.

But if you could line up a bunch of stars, including our sun, all at the same distance, you would see that some stars are brighter and some are fainter than our sun.

The biggest, heaviest stars can make more energy and shine more brightly than the sun. The smaller, lighter stars make less energy and shine less brightly than our sun. So it all depends on how big and heavy a star is. It's all due to gravity. The nebula consists of gases, mostly hydrogen, and also dust. The dust is just what you would expect, tiny rocky particles. If the nebula is cold and dark, denser blobs can form in it. Those blobs have gravity and can put surrounding gas and dust into them.

As they get bigger, they have stronger gravity and can pull more and more gas and dust to them. The inner layers of gas and dust start to warm from the pressure of the gas and dust above. The dust is vaporized and turned into gas. When the inner gases get hot enough, the blob — now a protostar, or very young star — begins to glow. At first it can be seen only in infrared light, but as it warms up and brightens it can be seen as a red star.

Now the star's heat and light blows away the surrounding gas and dust, and the new star can finally be seen in the nebula.

It sure can. In fact over half the stars in the sky are actually binary or triple stars, in which two or three stars formed together and are in orbit around each other. In addition, stars tend to form in large groups within huge dark clouds of gas and dust. There can be hundreds of stars forming in these big dark clouds. People have seen the stars overhead for thousands of years. Even though they didn't know what they were or had some odd ideas about that! The ancient Greeks said "aster" from which we get the word astronomy , while the Romans said "stella.

We give stars names so we can talk about them with each other. This is just like giving people names, so you can call your classmate "John" instead of "red-haired boy with freckles wearing blue jeans. The brightest stars have names that were originally Arabic in origin. For instance, the star Betelgeuse's name means "armpit" it is in the constellation of Orion, the hunter, at his armpit. Stars are listed in catalogs that give information like the position in coordinates similar to latitude and longitude on the earth , the brightness of the star, its color, and so on.