Again - these are all estimates, using the best-guess data we have; While the numbers could be far off - it's likely that they're at least in the ball park...
Same for the number of known galaxies; obviously, no one guy sat down and started counting them - it's an estimate based on how many galaxies could be seen in a few segments of the sky. Again, while it's only an estimate - it's thought that 100 to 200 billion galaxies is in the ball park, based on samples of the sky that have been analyzed.
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The Black Hole say: Direct inference. They pointed a telescope at a small section of the night sky and counted the number of galaxies that appeared. Then they extrapolate the total by multiplying the number of similar size sectors in the entire spherical sky by that measured number of galaxies in the sample. The universe is essentially homogenous and similar in any direction you look.
They infer the number of stars in a galaxy by a similar method. The number of planets per star is quite variable, so the value of 100 billion planets is not reliable. Its actually 100 billion stars per galaxy.
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ignoramus say: Actually, I made it 100 000 000 002 planets. I'll count it over.
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Stephen say: However they did it, remember that 100 billion planets does not equal 100 galaxies.
I am not referring to the difference in mass.
I am referring to the fact that whoever counted the planets probably isn't the same person that counted the galaxies. So we have no way of knowing whether 1 billion = 1 billion.
Some people's billions are 1000 times smaller than other People's billions.
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say: statistical analysis
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