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Stars brighter and hotter than the Sun are rare, whereas substantially dimmer and cooler stars, known as red dwarfs, make up about 75% of the fusor stars in the Milky Way. [ 80 ] The Sun is a population I star , having formed in the spiral arms of the Milky Way galaxy.
In plasma physics terms, it is the cavity formed by the Sun in the surrounding interstellar medium. The "bubble" of the heliosphere is continuously "inflated" by plasma originating from the Sun, known as the solar wind. Outside the heliosphere, this solar plasma gives way to the interstellar plasma permeating the Milky Way.
The Sun formed about 4.6 billion years ago from the collapse of part of a giant molecular cloud that consisted mostly of hydrogen and helium and that probably gave birth to many other stars. [125] This age is estimated using computer models of stellar evolution and through nucleocosmochronology. [13]
All remaining stars were regarded as "fixed" in the background. One important discovery made at different times in different places is that the bright planet sometimes seen near the sunrise (called Phosphorus by the Greeks) and the bright planet sometimes seen near the sunset (called Hesperus by the Greeks) were actually the same planet, Venus. [7]
The Sun was found to be part of a galaxy made up of more than 10 10 stars (10 billion stars). The existence of other galaxies, one of the matters of the great debate , was settled by Edwin Hubble , who identified the Andromeda nebula as a different galaxy, and many others at large distances and receding, moving away from our galaxy.
[19] [20] Studies of the structure of the Kuiper belt and of anomalous materials within it suggest that the Sun formed within a cluster of between 1,000 and 10,000 stars with a diameter of between 6.5 and 19.5 light years and a collective mass of 3,000 M ☉. This cluster began to break apart between 135 million and 535 million years after ...
Hipparchus also created a comprehensive catalog of 1020 stars, and most of the constellations of the northern hemisphere derive from Greek astronomy. [20] The Antikythera mechanism ( c. 150 –80 BC) was an early analog computer designed to calculate the location of the Sun , Moon , and planets for a given date.
It may also be considered a place between the ground and outer space, thus distinct from outer space. In the field of astronomy, the sky is also called the celestial sphere. This is an abstract sphere, concentric to the Earth, on which the Sun, Moon, planets, and stars appear to be drifting.