![]() ![]() This stage usually lasts around 100,000 years and, over time, gravity and pressure increases, forcing the protostar to collapse.Ī T Tauri star is the stage a star is at before it becomes a main sequence star. With the naked eye, we can perceive around 2,000–2,500 stars.Ī protostar is a collection of gas that has collapsed down from a giant molecular cloud. In fact, most of the main-sequence red dwarfs are too dim to be seen with the naked eye from Earth. The Sun is a main-sequence, yell0w dwarf G-type star, but most of the stars in the Universe are much cooler and have a low mass. The most common type of dwarf star is a main-sequence red dwarf star. The most common types of stars in our night sky, are dwarf stars. This system is known as the Morgan-Keenan (MK) system and was introduced by William Wilson Morgan and Philip C Keenan in 1943. The temperature of each spectral class is then subdivided by the addition of a number, 0 stands for the hottest while 9 for the coolest. The stars are classified based on their temperature, with the hottest being O and the coolest being M. There are 7 main spectral types of stars - O (Blue), B (Blue), A (Blue), F (Blue/White), G (White/Yellow), K (Orange/Red) and M (Red). Most stars form in groups called star clusters, but many are eventually ejected from these clusters. The heat generated by this nuclear fusion causes the gas to expand and, when hydrostatic equilibrium is reached, the star is born. The temperature and pressure continues to grow until hydrogen can be fused. This then causes the matter to heat up and glow while the mass increases. Gravity causes the clouds to contract, drawing the gas closer and, as these materials accumulate in the centre, density rises and pressure increases. Stars form in huge clouds of gas and dust. Astronomers grouped stars into constellations to track their movements and the position of the Sun. Stars have been used for celestial navigations and religious practices for many thousands of years. Each one is brighter than our Sun, but much further away so they appear much smaller or not at all to the naked eye. Our Milky Way galaxy contains an estimated 300 billion stars. They can also be classified by their spectra (the elements they absorb) and their brightness. There are many different types of stars in the universe and they can be categorised according to their mass and temperature.
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