A star is a glowing sphere of plasma, which is held together by its own gravity. Stars are the engines of cosmic energy which produce X-rays light, heat, Ultraviolet rays and other radiation forms. They are largely composed of plasma and gas. The Sun is the nearest star to the Earth. During the night, other stars are also visible from the earth. In the night sky, they become visible as a multitude of fixed luminous points because of their huge distance from the earth. The most well-known stars are grouped into Asterisms and Constellations, but the brightest stars have their proper name.
The Universe probably holds more than 100 billion galaxies and each of those galaxies may contain 100 billion stars. A star shines because of fusion (thermonuclear) of helium and hydrogen in its core. It releases energy which passes through the interior of the star and then emits into the outer space. A star can also have degenerate matter near the end of its life. Astronomers can determine the chemical composition, age, mass and many other properties of a star by examining its motion through the spectrum, space and luminosity. The characteristics of a star such as temperature and diameter can change over its life. Though, the environment of a star affects its movement and rotation.
Throughout the world, stars have been historically important to civilizations. They were an important part of religious practice and also used for orientation and celestial navigation. Astronomers used starts to track the motions of the planet and also to infer the position of the sun by grouping them into Constellations. The motion of the sun against the background stars was used to make calendars that can be used to adjust agriculture practices. In the 1534 BC, the oldest accurate star char chart became visible in ancient Egyptian astronomy. In 300 BC, with the help of Timocharis, the first star catalogue in Greek astronomy was made by Aristillus. Arabic names of stars given by the Medieval Islamic astronomers are still in use today. With progress came varied astronomical instruments to calculate the stars’ positions. Medieval Islamic astronomers also built the first large observatory research institute for the reason of creating “Zij “star catalogue. In the 11th Century, the Persian polymath researcher Abu Rhyhan Biruni described the Milky Way galaxy as a mass of fragments which have the properties of vague stars and in 1019, during the lunar eclipse, he also gave the latitudes of various stars.
Stars use near to about 90% of their lifespan in fusing helium and hydrogen in the reactions of high-pressure and a high temperature near the core. These types of stars are known as dwarf stars and they are said to be on the main sequence.
Everything about a star is determined by its size, initial mass, luminosity, lifespan and evolution. Most stars are about 1 billion and 10 billion years old. The more huge the star, it has a shorter lifespan because huge stars have better pressure on their core which cause them to burn hydrogen more quickly. In the present Milky Way galaxy, when star forms than they are composed of 27%Helium and 71% Hydrogen. Because of the enormous distance from the Earth, all stars become visible as shining twinkling points in the night sky to the bare eye. This twinkle is due to the effect of the atmosphere of the Earth. The Sun is also a star, but is close to the Earth and appears as a disk and also provides daylight.