Need help with a formula: Assume that there are approximately 140x10^9 stars...

[trad78]

Need help with a problem. For some reason I can not seem to get it correct. Thinking my formula is wrong. Here's the problem:

Assume that there are approximately 140x10^9 stars in our galaxy.
Our galaxy is 50,000 light years from the center to the edge, but just 1,000 light years thick. It's shaped like a thin disk or cylinder. If the stars were distributed equally throughout the galaxy, how many stars would you expect to find in one cubic light year?

I thought it would be Pi*r^2*l. Then divide that by the number of stars. What am I doing wrong? Thanks, been 20 years since I had to do math like this!

 

[Deleted member 4993]

Need help with a problem. For some reason I can not seem to get it correct. Thinking my formula is wrong. Here's the problem:

Assume that there are approximately 140x109 stars in our galaxy.
Our galaxy is 50,000 light years from the center to the edge, but just 1,000 light years thick. It's shaped like a thin disk or cylinder. If the stars were distributed equally throughout the galaxy, how many stars would you expect to find in one cubic light year?

I thought it would be Pi*r^2*l (Correct). Then divide that by the number of stars. What am I doing wrong? Thanks, been 20 years since I had to do math like this!

Is that supposed to be 144^(109) or 144¹⁰⁹

It needs to be = (no. of stars)/Volume

 

[trad78]

Ahhh, so I was dividing wrong? It is suppose to be 140*10^9. Sorry about that.

Does .01783 sound correct? I only have one more shot at answering the question correctly.

 

[ksdhart]

You might want to double check that you're reading your calculator correctly. Specifically, where did the 7 in your answer come from? When I do the math, I get 0.0183...

 

[trad78]

3.14*5000^2*1000 = 7.85*10^12
(140*10^9)/(7.85*10^12) = .01783

 

[trad78]

?

 

[ksdhart]

Huh. Well, I'll be. I was using the 144*(10^9) for the number of stars, as stated by Subhotosh Khan. I didn't notice until just now that the original problem says there are 140*(10^9) stars. I'll just go stand in the corner then. Sorry for the error.

 

[Ishuda]

Huh. Well, I'll be. I was using the 144*(10^9) for the number of stars, as stated by Subhotosh Khan. I didn't notice until just now that the original problem says there are 140*(10^9) stars. I'll just go stand in the corner then. Sorry for the error.

I think I still have a little time left on mine so we can keep each other company [but no talking seems to be the rule].

 

[trad78]

No problem! Well, I submitted the .0178 answer, and it was correct! Last chance to get it right. Thanks for the help.