Group V Stars
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Stars

A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun. Many other stars are visible without a telescope from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth

Some stars are in kind of formations called 'Constellations'. They all have different names like Big Dipper (Ursa Major), Little Dipper (Ursa Minor), Cepheus and Cassiopeia. These are all simple names for constellations.

In some nebulae, stars form out of large clouds of gas and dust; once some stars have formed inside the cloud, their light illuminates the cloud, making it visible to us. These star formation regions are sites of emission and reflection nebulae, like the famous Orion Nebula shown in the picture on the right. During its 'main sequence' period of its life cycle, a star is stable because the forces in it are balanced. The outward pressure from the expanding hot gases is balanced by the force of the star's gravity. Our Sun is at this stable phase in its life.

Massive stars are born, just like average stars, out of clouds of dust called nebulae. These stars have: A quick main sequence phase, where hydrogen continues to be fused into helium during a stable portion of the star's life cycle.

Outlined below are the many steps involved in a stars evolution, from its formation in a nebula, to its death as a white dwarf or neutron star. A nebula is a cloud of gas (hydrogen) and dust in space. Nebulae are the birthplaces of stars.

How Far Away Are The Stars?

The stars are not all at the same distance from us. Some stars are closer and some are farther away. The closer a star is to us, the brighter it will appear. Also, stars come in a variety of sizes and brightnesses. Larger stars usually shine more brightly than smaller stars do. So, how bright a star appears in the night sky depends on its size as well as how far away from us it is. The closest star is about 25,300,000,000,000 miles (39,900,000,000,000 kilometers) away, while the farthest stars are billions of times farther than that.

Astronomers have known for hundreds of years that stars have colors. If a star gives off ultraviolet waves, the star's color is blue, whereas if it gives off infrared waves, the star's color is red.

Modern instruments can measure very precisely the color of a star. This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths. The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[9] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.

For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

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