Group U Stars

What is a star?

We're all pretty familiar with stars. We see them on most clear nights as tiny, twinkling pinpricks of light in the sky.
Stars are the topic of countless poems, stories, and nursery rhymes alike. But just what is a star, exactly?

A star is a luminous ball of gas, mostly hydrogen and helium, held together by its own gravity. Nuclear fusion reactions
in its core support the star against gravity and produce photons and heat, as well as small amounts of heavier elements.
The Sun is the closest star to Earth.

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Stars are always in the sky. We see them at night shining ever so bright but not in the day.
In fact, stars are even there in the day but we just can not see them because they are
so much fainter than the sunlight scattered by our atmosphere.

If the Earth had no atmosphere at all, then our daytime sky would be pitch black like at night, except
the sun would be a huge spotlight shining down upon us.

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The intense extre forceand temperature at the core of a star allow nuclear fusion reactions to take place.
This is where atoms of hydrogen are fused into atoms of helium.
This reaction releases an enormous amount of energy in the form of gamma rays.

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Energy is produced in a star's center, or core, where pressures are enormous and
temperatures reach 27 million°F.This causes nuclear fusion—atoms of hydrogen are
ripped apart and join to form helium. These reactions release vast amounts of energy, which makes the stars shine
beautifully at night.

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A galaxy is a large collection of stars.

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Stars are usually between 1 and 10 billion years old. Some stars may even be close
to the age of the observed Universe at nearly 13.8 billion years old.

After the Sun in our Solar System, the nearest star to Earth is Proxima Centauri. It is about 39.9 t
rillion km away or 4.2 light years. This means it takes light from this star 4.2 years to reach Earth.
Using the newest, fastest space probe propulsion systems would still take a craft about 75,000 years to get there.

Big stars like supergiants and hypergiants have shorter lives as they consume their fuel at a
faster rate than smaller stars. As these massive stars die they explode as massive bright supernova.

Very heavy stars that have gone supernova can actually turn into black holes.
black-holes.jpgHere is an image of two black holezs merging together.
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What is a shooting star?

Shooting stars look like stars that quickly shoot across the sky, but they are not stars.
A shooting star is really a small piece of rock or dust that hits Earth's atmosphere from space.
It moves so fast that it heats up and glows as it moves through the atmosphere.

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Shooting stars are actually what astronomers call meteors. Most meteors burn up
in the atmosphere before they reach the ground.
However, once in a while a meteor is large enough than some of it survives and reaches Earth's surface.
Then it is called a meteorite.

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