## So, just how many stars are there up there?

john
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### So, just how many stars are there up there?

This is really a serious question asked in a childlike way. It is usually answered not with a number, but with an analogy-most frequently something like: "more than all the grains of sand on all the beaches in all the world."

Well, is that just surface layer sand, or can we dig down to rock and count the grains in between. Is that at hightide or lowtide? That is the first thing I wonder whenever I read the above answer.

So, the real qurestion is, if it has a realistic known answer, is:
What is the mathematical approximation of all the stars in the universe?

Come on, please, I'm waiting, for years I've waited. I have and know children who want to know. Please.

Seriously, and not Dr. Carl Sagen's "billions and billions" but a number like 1 followed by ? zeros or 10 raised to ? power, something like that.
Last edited by john on Fri Jun 17, 2005 1:31 pm, edited 1 time in total.

makc
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makc
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Here's another one.

BMAONE23
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### Just my 2 cents

I like the second answer better. It seems to be more descriptive.

Beorn
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I like this number as well, the estimated total number of atoms in the observable universe

http://en.wikipedia.org/wiki/Atom
Atoms in the universe and our world

Using inflation theory, the number of atoms in the observable universe can be estimated to be between 4×10^78 and 6×10^79. However, because of the possibly infinite nature of the universe, the total number of atoms in the entire universe may be much larger or even infinite. This does not change the estimated number of atoms in the observable universe since that is the number of atoms within about 14 billion light years of us - which is all that we can observe since the universe is only about 14 billion years old.

Dale
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Hello all . . I just joined this forum and this is my first post. I'm not sure whether this reply should be a separate subject, but I too have been interested in "how many stars are up there". although I would like to limit the count to the Milky Way. The literature I have seen (as an amateur layman) puts the count from 1E11 to 1E12. That's much to imprecise to draw any conclusions.

Recently I have wondered what impact the calculations on dark matter have affected the calculations on the amount of baryonic matter in our galaxy. Most accounts seem to put the (baryonic?) mass at about 2X11 solar masses and the discussion revolves around to allocate this mass to the various classes of stars. For example Class M stars probably account for 75% of the total number.
Dale

ihowarth
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Turns out that it's really quite hard to determine the mass of/number of stars in our own galaxy very accurately, but even the range
10^11-10^12 solar masses is good enough to get a handle on the "grains of sand vs. numbers of stars" issue. I set this as an elementary question for an introductory cosmology course, and in consequence yet another answer is available at
http://www.star.ucl.ac.uk/~idh/3C36/P2005/3c36a1.pdf

(don't be too concerned about the somewhat more mathematical later parts of the questions sheet!)

Dale
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### Milky Way Census (How many Stars?)

Thanks for replying ihowarth. I used your web link and read the article. Still, I'm not satisfied. My end goal is to determine a number (acceptable to me) of the percentage and number of stars of each class in the thin disk. I believe this might give a more acceptable estimate of the number of stars that can support life. More specifically, I'm searching for the Goldilocks stars - ones that live long enough for evolution to have produced higher lifeforms (less than F class) - have enough metalicity to have rocky planets (thin disk) - and have a wide enough "green zone" to contain liquid water (the larger M class stars).

tanq10
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### The Drake Equation?

Ah, Dale, your last message indicates you might be trying to discover the answer to the Drake equation:

http://www.airynothing.com/smackerels/D ... ation.html

Good luck!

Will

Dale
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Yes, you are correct . . I AM trying to refine the parameters. In spite of all the new telescopes and fancy computers, it seems we are no closer to an answer then we were when Dr Drake formulated his equation. Here's the web site I prefer on the subject.

Beyond the Drake Equation at
http://www.station1.net/DouglasJones/drake.htm[/url]

tanq10
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### Nova's Drake Equation "Origins" Episode

I've not had much interest in ETs so I don't know if this is a reasonable treatment of the equation, but there was a Nova on PBS called "Origins" which ran through the equation by interviewing experts on the subject. I found it interesting... Might want to program Tivo for to record it the next time it's on (if you're lucky enough to have Tivo, that is).

Following is a URL to the episode's description:

http://www.pbs.org/wgbh/nova/origins/drake.html

The site even has an interactive Drake Equation calculator that's fun to play with. It defaults to 10,000 ETs in the Milky Way who able to communicate.

Will