# How do astronomers count stars in the Milky way? (procedure, method)

## Main Question or Discussion Point

Hey guys,

What method do astronomers use to count the stars in the galaxy to come up with a number ?

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Chronos
Gold Member
It is an inexact science, not a hand count. Gravity is one method.

What method do astronomers use to count the stars in the galaxy to come up with a number ?

For "*the* galaxy," e.g. our galaxy, it is complicated and inexact as Chronos points out, but the basic idea is something like the following:

1) count the ones observable (using all-sky surveys and computer programs)
2) figure out what region of the milky way these stars are in (e.g. their distance and direction away)
3) use statistics to account for selection biases (e.g. we only see the brighter, nearer stars) to generalize to the total number of stars in the galaxy.

Thanks for that!!

Answer me this if you can.

Lets say one way is to use a sampling method. How can we count/sample the stars when we are inside the milkyway? Or, how can we use simple methods to count stars we can see in the sky, or on a all sky survey?

Can you get a good picture of a all sky survey?

Check this out, for example: https://www.cfa.harvard.edu/~rkirshner/MilkyWay.jpg
I'm not sure what kind of images they actually use for such estimates however.

Lets say one way is to use a sampling method. How can we count/sample the stars when we are inside the milkyway? Or, how can we use simple methods to count stars we can see in the sky, or on a all sky survey?
I'm not entirely clear on what you're asking. We know our basic position in the milky way, so if we could the stars near us (the ones we can easily see) we can try to compensate (statistically) for our position... also, one could use the direction dependence of the observed population of stars (very apparent in the above link), to construct an analytical model for the milky way's stellar distribution---then integrate to estimate the total.
Does that help?