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If the universe is infinite, scientists assume that the number of celestial bodies that compose it must also be infinite. We can only count the number of stars that are in the visible part of the cosmos, the one whose light reaches the Earth. For starters, that includes no less than 100 billion galaxies – large star systems like the Milky Way, which encompasses our entire Solar System. “These galaxies can contain from a few million stars, in the case of the smallest, to hundreds of billions, in the case of the most luminous ones”, says astronomer Laerte Sodré Jr., from USP. With an average of 100 billion stars per galaxy, this estimate will reach a trifle of ten sextillion stars! (To get an idea of what a sextillion means, add a row of 21 zeros to the number one.)
Compared to that number, the amount of stars we see through the window represents almost nothing: only 5,000 are visible from Earth with the naked eye. Galaxies, then, we only see four without a telescope: the Milky Way, of course, plus Andromeda and the two Clouds (Small and Large) of Magellan.