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The observable universe contains as many as an estimated 2 trillion galaxies [36] [37] [38] and, overall, as many as an estimated 10 24 stars [39] [40] – more stars (and, potentially, Earth-like planets) than all the grains of beach sand on planet Earth. [41] [42] [43] Other estimates are in the hundreds of billions rather than trillions.
Star count programs can therefore collect data that bounds or determines these values. [2] One of the interests of astronomy is to determine how many stars there are of each of several types that stars can be categorized into, and how these stars are distributed in space.
This illustrates the fact that there are far more faint stars than bright stars: in the entire sky, there are about 500 stars brighter than apparent magnitude 4 but 15.5 million stars brighter than apparent magnitude 14. [108] The apex of the Sun's way, or the solar apex, is the direction that the Sun travels through space in the Milky Way.
More than 100 OB and Wolf–Rayet stars have been identified there so far. [47] They seem to have all been formed in a single star formation event a few million years ago. The existence of these relatively young stars was a surprise to experts, who expected the tidal forces from the central black hole to prevent their formation. [48]
Overall, there are likely to be between 10 22 and 10 24 stars [108] [109] (more stars than all the grains of sand on planet Earth). [ 110 ] [ 111 ] [ 112 ] Most stars are within galaxies, but between 10 and 50% of the starlight in large galaxy clusters may come from stars outside of any galaxy.
The following is a list of particularly notable actual or hypothetical stars that have their own articles in Wikipedia, but are not included in the lists above. BPM 37093 — a diamond star Cygnus X-1 — X-ray source
All stars but one can be associated with an IAU (International Astronomical Union) constellation. IAU constellations are areas of the sky. Although there are only 88 IAU constellations, the sky is actually divided into 89 irregularly shaped boxes as the constellation Serpens is split into two separate sections, Serpens Caput (the snake's head) to the west and Serpens Cauda (the snake's tail ...
G-type stars, including the Sun, [14] have prominent spectral lines H and K of Ca II, which are most pronounced at G2. They have even weaker hydrogen lines than F, but along with the ionized metals, they have neutral metals. There is a prominent spike in the G band of CN molecules. Class G main-sequence stars make up about 7.5%, nearly one in ...