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I have heard multiple estimates on the quantity of stars within our galaxy, anything from 100 to 400 billion of them. The estimates seem to be increasing for the time being. What are the main methods that are used to make these estimates, and why are there such large discrepancies between them?

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2 Answers 2

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The estimates I've read are similar to yours: 200 to 400 billion stars. Counting the stars in the galaxy is inherently difficult because, well, we can't see all of them.

We don't really count the stars, though. That would take ages: instead we measure the orbit of the stars we can see. By doing this, we find the angular velocity of the stars and can determine the mass of the Milky Way.

But the mass isn't all stars. It's also dust, gas, planets, Volvos, and most overwhelmingly: dark matter. By observing the angular momentum and density of stars in other galaxies, we can estimate just how much of our own galaxy's mass is dark matter. That number is close to 90%. So we subtract that away from the mass, and the rest is stars (other objects are more-or-less insignificant at this level).

The mass alone doesn't give us a count though. We have to know about how much each star weighs, and that varies a lot. So we have to class different types of stars, and figure out how many of each are around us. We can extrapolate that number and turn the mass into the number of stars.

Obviously, there's a lot of error in this method: it's hard to measure the orbit of stars around the galactic center because they move really, really slowly. So we don't know exactly how much the Milky Way weighs, and figuring out how much of that is dark matter is even worse. We can't even see dark matter, and we don't really understand it either. Extrapolating the concentrations of different classes of stars is inexact, and at best we can look at other galaxies to confirm that the far side of the Milky Way is probably the same as this one. Multiply all those inaccuracies together and you get a range on the order of 200 billion.

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Good answer. In short: we look at a small sample of the Milky Way near us and figure out how many stars it has and how much it weighs, then we figure out how much the whole galaxy weighs, and we estimate from there. –  Wedge Jun 5 '11 at 10:15


How many stars are in the Milky Way Galaxy?


As many as there are!

Why this answer?


Even the stars that are close to us are eons older than when their light approximately began to journey toward all directions including Earth.

Unknown & thus far unprovable amount of celestial activity continues from when ever it became the what we call the Milky Way Activity.

There is much evidence that the Galaxies including ours continues to expand. Stars are forming while others transform into altered states even making possible other Stars to Form.

How can we determine this?

More data, more time & more true scientific method not beholding to any unscientific influences.

The many formulas used to guesstimate stars in galaxies can help us grasp concept & appreciation.

Example. If there were trillions of stars in a galaxy; Saying there are so many billions would not be wrong. There would me. It would just be less accurate & not help us understand that we as humans now with the equipment & data available may accidentally guess the answer yet not be able to confirm.

By the time we could confirm if we could, there would be stars coming & going. No finite answer.

Saying "AS MANY AS THERE ARE!" A person can enjoy the "AWE!" That can be experienced being on a planet, circling a star amongst uncountable amounts of stars with planets making up a group of stars we can give a finite name :MILKY WAY"! So many stars close together it is like endless amounts of "WHITE MILK!" MILKY WAY IS LATIN FOR: Via Lactea which translates literally as Road of Milk and is so called because of the pale band of light formed by stars in the galactic plane as seen from Earth. It appears to be a milky patch of sky that rings the Earth.

Read more: http://www.universetoday.com/84662/why-is-our-galaxy-called-the-milky-way/#ixzz2us0fwAxF

As always, this was the short answer. :)

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protected by Qmechanic Apr 3 at 3:37

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