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answers:
an say: Scientists worked out the total mass of the Milky Way by observing the movement of the stars, then they use our sun mass to work out the number of stars in the galaxy.
The take years of observation of planet systems in the galaxy to work out the number of planet per star, they arrived at 1 planet per star.
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Michael say: HOGWASH. Mike
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spot a say: They counted some stars in a small area then multiplied by the size of the galaxy. Same with galaxies, count some and multiply
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Brigalow Bloke say: Essentially the same way as you estimate the number of plants in a plot of ground, people in a photograph of a large crowd, bacteria in a petri dish etc.
Divide the sky up into say 500 segments, then count all the galaxies in say 20 randomly distributed segments. Multiply by 25 and that's your estimate. The more segments you count, the more accurate your estimate. But once your sample is over a certain size, counting more does not make much difference to your final result. Statistical mathematics will show you the minimum and maximum number of segments you need to count.
Gallup and other polls use the same principle.
I don't know how they do stars in galaxies, but it might be based on the brightness and spectrum.
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Donut Tim say: By looking.
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say: 100 billion guesses of course.
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say: I wonder the same
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quantumclaustrophobe say: The number of stars in our galaxy is an estimate; on the low end, it's thought that there's 100-150 billion stars; on the high end, 300-400 billion. In the middle - is about 200 to 250 billion stars.
The number of exo-planets we've been finding suggest that *most* stars have planets; we don't know if they all do... but, conservatively, it's been estimated that there's an average of 4 planets per star in the Milky Way - which actually gives us about 1 *trillion* planets in our galaxy alone.