What is a Star Made of?
Every Bright star is a sun, like our own sun. This means that stars are huge globes of glowing gas. They are so hot that if a piece of steel were placed there. it would disappear in a puff of gas. In many of the stars, the gases are very thin. This is because of the atoms, of matter in the gas, are so far apart.
But the stars do have a matter in them. For example, the sun contains more than 60 of the chemical elements present in the earth. Among the elements in the sun are hydrogen, helium, iron, calcium, and magnesium.
In cooler stars, the matter may be more nearly liquid. It may be somewhat like the boiling iron in the blast furnace. In some very old and cold stars, the matter may be so densely packed that a cubic inch of it would weigh a ton. such stars are called “dead” or “dark stars”.
Astronomers can find out all this by using instruments called “spectroscopes”. The spectroscope studies the light a star gives. From this, we can learn what kinds of matter it contains and how hot it is.
The different colors of the stars, white, blue, yellow, red indicate what chemical elements are present in them. Different temperatures of stars also cause differences in the light they give in their spectrum. In this way, the temperature of a star can be determined.
What Makes The Stars Shine?
A Star is a ball of very hot gas which shines by its own light. Planets and our Moon, shine only by light reflected from the sun. And planets shine with a steady light while stars appear to twinkle. This is caused by substances in the air between the star and the earth. The unsteady air bends the light from the star, and then it seems to twinkle.
Why does our sun shine? because it is a star! and not a very big or bright star at that. compared to all the other stars in the sky, it might be considered medium-sized and medium-bright. There are millions of stars that are smaller than our sun. And many stars are several hundred times larger than the sun. They look small only because they are so far away.
Ever since the days of the Greek astronomers, some 2000 years ago, the stars have been divided into classes according to their “magnitude”, or brightness. Another way of grouping stars is according to their spectra, or the kind of light that comes from the stars. By studying the differences in these spectra, the astronomer may learn about the colors, temperature, and even the chemical composition of the stars.
Why Are Some Stars Brighter Than Others?
When we look up at the sky, we do not see too many differences among the stars. Some look a bit bigger than others. But we really cannot get a good idea of the tremendous differences that exist among them.
One way of classifying stars is by their spectra- a spectrum is a breakdown of the light given off. In this way, stars range from blue stars to red stars. Our sun is considered to be yellow and is in the middle of the series.
The blue stars are large and hot and brilliant. Their surface temperatures may be as high as 27,750 degrees or more. The sun is medium bright and has a surface and has a surface temperature of 1,650 degree or less. So you can see that some are very much brighter than others, but because of their great distance from the earth we are not aware of it.
The brightness of a star is called its “magnitude”. A star of any given magnitude is about two and a half times fainter than a star of the magnitude above it. So magnitude is a sort of scale for measuring brightness. Stars fainter than the sixth magnitude cannot be seen without a telescope. Stars of the first magnitude are the brightest, and there are about 20 such stars we know of. But there are at least a thousand million stars that are only of the twentieth magnitude.
How Many Stars Can We See At Night?
“Countless as the stars at night.” This is the impression we get of the sky when we look up at night and see the stars. But it may surprise you to know that only 6,000 stars can be seen without telescope.That does not mean a person can look up and count 6,000 stars. Because one-fourth of these 6,000 stars are too far south to be visible in Western Europe. And of of the stars that can be seen from any one place on earth, only one-half are visible at one time as the others are below the horizon.
What’s more, many of the stars near the horizon cannot be seen because of haze. So what do we end up with? If you started to count the stars that you could see, you would probably not be able to count many more than 1,000.
Photographs can be taken of the same sky by a camera attached to a telescope. Many more stars can be counted on a photograph of a particular spot in the sky than the unaided eye can see there. And with a time exposure, even more stars will be added.
Finally, by using a very powerful telescope, it would be possible to photograph more than 1,000,000,000 stars!
catlogue of the stars
Once a star is noticed in the sky it must be given a name or an identification number. Long ago, people in many lands- the Arabs, the Greeks, the Romans, and the Chinese-gave names to the brightest stars and to other stars that were in some way remarkable. More than 100 stars were given names.
And man has wanted to have a catlogue of the stars that were known. The first known star catalogue listed 1,025 stars and dated from about A.D 137. A modern catalogue of the stars lists more than 457,000 stars!
What Are The Nearest Stars?
Sometimes we can measure something- and yet have no real understanding of what that measurement means. When it comes to distances in the universe, for example, we are able to measure them, but our minds cannot really grasp what that means in terms of our life.
For distances in the universe, a special unit of measurement was set up, called “the light year”. A light year is simply the distance a ray of light will travel in a year. Since light travels about 186,000 miles a second, in one year it will travel a distance of nearly 6,000,000,000,000 (six billion) miles!
The closest star to us is Proxima Centauri, and this is about four and a third light years away. That means a distance of 26 billion miles! This star can be seen from the Southern Hemisphere. The nearest star in the Northern Hemisphere is Sirius. It is eight light years away.
The farthest stars we can see with the naked eye are about 8,000,000 light years away. When we look through times farther away. Through such telescopes, stars six thousand trillion miles away can be seen. The light from these stars started out a thousand million years ago on its way to the earth!