Do astronomers know how many galaxies exist? How many can we see in the observable Universe?
How many galaxies are there in the Universe, and is this even something that we can calculate?
Simplistically, the number of galaxies in the universe will be the size of the Universe times the average number density of galaxies. In practice, it is difficult to estimate these two numbers accurately.
The total size of the universe is unknown. Recent research suggests it may be infinite, implying that there could be an infinite number of galaxies.
However, there is a limit beyond which we cannot see; because light from beyond has not had time to reach Earth since the Big Bang.
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It is estimated that the ‘observable universe’ is a sphere with a diameter of about 92 billion lightyears and a volume of about 410 nonillion (410 thousand billion billion billion) cubic lightyears!
Estimating the number density of galaxies presents its own problems.
It is not possible to simply count all the galaxies in the sky. It would take too long.
Besides, even the best telescopes would miss galaxies that are too faint, too small or too close to other galaxies — as well as ones which are obscured by intervening material or do not emit light detectable by the telescope.
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This technique will, however, give you a lower limit to the number of galaxies. One such estimate says that there are between 100 and 200 billion galaxies in the observable universe.
Other astronomers have tried to estimate the number of ‘missed’ galaxies in previous studies and come up with a total number of 2 trillion galaxies in the universe.
However, based on recent measurements of the darkness of the night sky, this may be an overestimate.