# Need Help with Astronomy Homework



## kittenamos (Jun 23, 2011)

I don't understand the math side of this class. Can someone explain to me how to solve these problems?

1) The thickness of the plastic in plastic bags is about 0.001 mm. How many wavelengths of red light is that?

3) Compare the light-gathering power of one of the 10-m Keck telescopes with that of a 0.5-m telescope.


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## MrKappa (Mar 18, 2013)

Wavelengths are nano meters.

So my guess is add one zero... or check google, try searching...

0.001 milimeters to nanometers... I got...

0.001 millimeters = 1000 nanometers

Hmmnnn... the other one sounds as if it may be a magnitude question.

So, divide one into the other? 20x as powerful?

I was searching the math, and found your question. It is indeed a magnitude question, and here is the long answer...

http://answers.yahoo.com/question/index?qid=20090323184347AAxsFjR

So my answer may be wrong as they came up with 100x stronger.

The correct math is (10 m / 0.5 m)^2 = 400x

I would have guessed (10 m / 0.5 m) = 20x, thus I skipped a dimension.


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## kittenamos (Jun 23, 2011)

MrKappa said:


> Wavelengths are nano meters.
> 
> So my guess is add one zero... or check google, try searching...
> 
> ...


Thanks a lot!! This was a big help. :clap


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## kittenamos (Jun 23, 2011)

failoutboy said:


> Do you have a kitten named Amos?


Haha, I used too. We had to give him away.


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