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When we look at the sky in a clear summer night we can see thousands of stars. But what is a star?
According to astronomic definition a star is: ”a space object that can produce its own light and heat".
It's a giant ball of gas held together by its own gravity. The gravity is always trying to make the star collapse, but this is counteracted by the pressure of the gas inside it. There are also a lot of radiation and nuclear reactions.
There are many ways to look at the stars. Poets see them as the beloved woman's eyes.
People who are dating just love to look at the stars at night.
By the way, where do stars go during the day?
They don't go anywhere, of course. They stay there in the sky. We just can't see them because the Sun light overcomes stars light.
Does that mean our Sun is the brightest star in the universe?
Of course not. But it is the nearest of all and that's why it seems so bigger and brighter than other stars. If you put an apple in front of your eyes it will seem to you bigger than a mountain many miles away, got the idea?
In fact our Sun is a medium sized star. There are many other a lot bigger. After the Sun the nearest star is Alpha Centauri four light years away. Oops! Another technical word! "Light year" what is it?
Very simple: It’s the distance a light beam can travel in one year. If you remember your high school classes you know that the light speed is about 300,000 kilometers/second. That means light can go from earth to Moon in about 1,5 seconds. That’s really fast, isn't it?
In one year the distance will be something around 1,2 or 1,3 billion kilometers (very far isn't it?)
Alpha Centauri is 4 light-years away, and it's the nearest star, can you imagine that?
There are stars and galaxies hundreds, thousands and millions of light-years away. The universe is really hard to imagine, not to mention to understand it.
Star colors can be yellow, white, blue or red depending on its age or stage. Stars, like everything else in the universe, have a lifetime. They begin, get old and die. But a lifetime of a star is measured in billions of years.
Our Sun is a middle-aged star, which means it still has some billion years to live. A star burns hydrogen turning it into helium and in the process it generates heat and light that makes life possible on the surrounding planets.
Astronomers explain that the huge gravity in a star is always trying to smash it. The pressure makes the star begin burning as a reaction against gravity.
The process is similar to an atomic explosion happening in slow motion. After some billion years the star has burned almost all the possible material and that makes gravity diminish. This makes the star expand till about ten thousand times the original size.
In the process it involves the planets what makes the mass grow again. Then it collapses and explodes as a "Super Nova". This is basically the life cycle of a star. Does it mean our Sun is going to collapse and destroy our planet in the future? Yes, it will, but take it easy! We still have some billion years to destroy the planet before the Sun does it.