Why do stars stop shining

Bethe won the Nobel Prize in Physics for his work concerning energy production in stars. Planet Earth, our bodies, and shining stars are all made of the same basic elements of matter. To understand why stars shine, we must first understand the tiny particles that make up matter. Scientists have studied matter in their laboratories for many, many years. Each kind of atom has a certain unique number of particles called protons, neutrons, and electrons in it. The protons and neutrons cluster together in the center of the atom in what is called the nucleus.

The electrons orbit around the nucleus. Atoms are very, very small. A hundred million atoms placed side-by-side in a row would only be about 1 inch long! The simplest atom is hydrogen. The nucleus of a hydrogen atom consists of a single proton. Around this proton orbits a single electron. There is more hydrogen in the universe than any other kind of atom. Helium is the second lightest or simplest atom. It consists of a nucleus containing 2 protons and two neutrons.

Around the nucleus orbits 2 electrons. Then the image was the smallest and most stable the icy cirrus clouds form in very calm air. I think of stars being rather faint because they are so far away! Most stars are very similar to our sun. In fact the sun is a pretty normal kind of star. It's much brighter than the other stars because it is close by. Even the closest star other than the sun is very far away. To give you an idea of how far, we can compare the time that it takes for light to travel from one place to another.

Light is very, very fast; it travels , miles in one second. Even so it takes about eight minutes for light to travel from the sun to the earth. How long does it take for light from the sun to travel to the nearest star?

When you look at the stars at night, some are closer and some are farther. Most of the stars that are the brightest are also the closest to us. The farther away the star is, the fainter it is. Well, no, stars are not on fire although they look that way.

We sometimes talk about them "burning," which can be confusing because we don't mean burning as in fire. Stars shine because they are extremely hot which is why fire gives off light — because it is hot. The source of their energy is nuclear reactions going on deep inside the stars. In most stars, like our sun, hydrogen is being converted into helium, a process which gives off energy that heats the star. The inside is actually millions of degrees, extremely hot! That warms the outer layers of the star, which gives off heat and light.

Something that is on fire, like the wood in a fireplace, requires oxygen to burn. The temperature of such a fire is hot, but not as hot as a star! 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. This is because the mass of the combing hydrogen is greater that the end product of helium.

Therefore, the mass is converted to energy, and that energy is the electromagnetic radiation light that we get from the Sun! Interactive Applet: Fusion in the Sun! Try out this excellent interactive applet that lets you play around with different variables in order to generate fusion in the sun! How Stars Work This is a good article that looks at how stars work. Nuclear Fusion Learn about nuclear fusion. Never Stop Exploring!!!