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Current estimates for the number of stars in the universe are about 10^22. However, that number has changed several times as new observations have come forth. How has the estimate of the number of stars in the universe changed over time? What was the estimate after Hubble's findings? What was the estimate in the 70s, 90s, etc., and what new discoveries forced those estimates to change?

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  • $\begingroup$ Until around the early 1900s, no other galaxies were known... it has likely affected the estimations a little bit. But statistical methods in the astronomy were far lesser common. $\endgroup$ – peterh May 31 at 22:16
  • $\begingroup$ Thanks. I'm curious how estimates changed since the advent of modern radio telescopes etc. For example, were estimates ever 10^18, 10^19, etc.? $\endgroup$ – user27343 May 31 at 22:25
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Do you mean the observable universe? We can only see stars whose light has reached us since the big bang, but the universe is much larger. We don't even know whether it is infinite. This article discusses estimates since 1995, giving a current estimate of $10^{24}$.

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Ptolemy's star catalog, which probably goes back to Hypparchus contains 1022 stars. It contains most of the stars visible by the naked eye in the Northern hemisphere. I do not think this number was substantially increased until the invention of the telescope. Flamsteed star catalog (made when the telescopes were already widely used) contains 2554 stars, but it was already known at that time that Milky way consists of stars. Nobody even tried to count them. That there are other galaxies besides the Milky way was discovered only in 20th century, and their stars cannot be counted but their number can be only roughly estimated, from average density of stars in a galaxy and its side. Similarly we estimate the total numbers of stars, using the average density of galaxies, number of stars in a galaxy and the radius of the universe (which comes from the Hubble law).

Of course, there was a period when people speculated that there are infinitely many stars, roughly speaking, this period lasted from Copernicus and Bruno to the end of 19th century.

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