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Star density maps of the Gaia Catalogue of Nearby Stars.The Sun is located at the centre of both maps. The regions with higher density of stars are shown; these correspond with known star clusters (Hyades and Coma Berenices) and moving groups. This is a list of nearby stellar associations and moving groups.
Thus, the Sun occupies 0.00001% (1 part in 10 7) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly 1 millionth (10 −6) that of the Sun. Jupiter, the largest planet, is 5.2 AU from the Sun and has a radius of 71,000 km (0.00047 AU; 44,000 mi), whereas the most distant planet, Neptune, is 30 AU ...
Star formation theory, as well as accounting for the formation of a single star, must also account for the statistics of binary stars and the initial mass function. Most stars do not form in isolation but as part of a group of stars referred as star clusters or stellar associations. [2]
Of the main-sequence star types, stars more massive than 1.5 times that of the Sun (spectral types O, B, and A) age too quickly for advanced life to develop (using Earth as a guideline). On the other extreme, dwarfs of less than half the mass of the Sun (spectral type M) are likely to tidally lock planets within their habitable zone, along with ...
The Ursa Major Moving Group is one example of a stellar association. (Except for α Ursae Majoris and η Ursae Majoris, all the stars in the Plough/Big Dipper are part of that group.) Other young moving groups include: Local Association (Pleiades moving group) Hyades Stream; IC 2391 supercluster; Beta Pictoris moving group; Castor moving group
Often they contain star clusters within them. The stars appear closely packed, but are not usually part of any structure. [18] Within the Milky Way, star clouds show through gaps between dust clouds of the Great Rift, allowing deeper views along our particular line of sight. [19] Star clouds have also been identified in other nearby galaxies. [20]
Proxima Centauri is the closest star to the Sun at 4.2465 light-years (1.3020 pc). α Centauri A and B are Sun-like stars (class G and K, respectively) that together form the binary star system α Centauri AB. To the naked eye, these two main components appear to be a single star with an apparent magnitude of −0.27.
Astronomers can determine stellar properties—including mass, age, metallicity (chemical composition), variability, distance, and motion through space—by carrying out observations of a star's apparent brightness, spectrum, and changes in its position in the sky over time. Stars can form orbital systems with other astronomical objects, as in ...