On earth, during a cloudless night, while sunlight does not outshine the stars, 2,000 to 3,000 stars can be seen by the naked eye. They crowd the night sky and it is impossible to count them without using any tool. The number of stars that people see every night change as the Earth revolves around the sun. Since the Earth is a sphere, people on the northern hemisphere do not see the same stars that people who live in the southern hemisphere do. When seen from Earth the stars appear to twinkle or the light around them appears to dance. This is because of the Earth’s atmosphere and not because starlight really sparkles. Up close, stars are extremely huge and glowing balls of compressed hydrogen and helium. The sun, which is the only star that exists inside the solar system, doesn’t glitter like how the stars do, because of its proximity to Earth.

Billions of light years away, an impossible to count number of stars surrounds the earth and the solar system. They come in different sizes and colors. Their sizes range from 20 kilometers to .9 billion kilometers. They are believed to have been part of the universe since 10 billion years ago or possibly around the age of the universe. New stars may still be born and those that exist now still continue to evolve and change over time. Outside the solar system are approximately 100 billions of stars that are clustered and held together by their gravity inside the milky way, which is the galaxy where the solar system is located.

A star is believed to form inside a galaxy from a molecular cloud, which consists mainly of hydrogen, about 25% helium and some denser elements. The explosion or collision triggers gravitational instability inside the clouds and as this continues, the cloud will reach the minimum density that is needed for the formation to start collapsing under its own gravitational force. As it collapses, the gravitational power is then converted into heat and this gives the formation an extremely high temperature. When it reaches equilibrium or hydrostatic balance, a protostar will form in the middle and this is often enclosed by a protoplanetary disk. This is just the beginning, the star will continue to evolve in several million years and will eventually die out or collapse.

When the universe was first formed, around 13 billion years ago, it is believed that the universe expanded from a hot and dense state and resulted to the formation of galaxies. Each galaxy is possibly made up of millions of clusters of different types of stars. Each galaxy may be compared to a sack full of peas. The whole universe is believed to be 93 billion light years wide and this means that there is an unbelievably large space to fill up. Inside the observable universe, it is assumed that billions of galaxies exist. This means billions of trillions of stars. The universe is like a football field with the earth as a microscopic dust. And there may be more of it outside of the already huge space that humans can presently observe.

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