Historically stars have been fascinating man. They made patterns with them to group them and they used them to find their way during voyages. Scientific research has been done extensively to understand their nature. Stars are defined as bodies that contain plasma that are held together with gravity. The star that is closest to earth is the sun. It produces vast amounts of energy that is being used in the earth for the sustenance of animal and plant life.
Due to massive stellar explosions that take place, gravitational instabilities occur within molecular clouds. Due to this reason, higher density regions occur. When such a region gains a certain density, they collapse due to their own density. When this happens, individual globules of dust and gas form. When these globules collapse the gravitational force increases and heat generates. Once this protostellar cloud comes to the level of hydrostatic equilibrium, the formation of a protostar begins.
Around 90% of its lifetime, a star fuses hydrogen to produce helium emitting energy. These are stars that are in main sequence. At the early stages the proportion of helium in the core of the star will rise steadily. As a result, the star will increase in luminosity and the temperature. This has occurred in the sun 4.6 billion years ago.
Most of the stars we see are 1billion to 10billion years old. Some stars are as old as 13.7 billion years, which is equivalent to the age of the Universe. The larger stars have shorter life spans as they convert hydrogen into helium faster. Their age will be a few billion years. But a smaller star may be active for up to hundred billion years.
Stars in the Milky Way consist of 71% hydrogen and 27% helium with little heavy elements by mass. Though the stars that we see in the night sky look like twinkling little bodies they are also similar to the sun which is also a star. Due to their distance they are not able to emit heat or light in sufficient quantities to reach earth.
Rotation, radiation and the temperature of stars are measurements that are important when you study them. Young stars may rotate at 100km/s at their equators and old ones may have speeds up to 225km/s. When it comes to temperature there are some that have over 5,000K. Some of the stars have 100 to 150 times of the mass of the sun but their life time is short.