# Emission spectrum?

1. Apr 23, 2007

1. The problem statement, all variables and given/known data

Ok guys, Helping my girlfriend out once again. She(if you haven't seen this before) is in Physics 101....yet, I(have taken all engineering courses) can't figure these out. Their book is absolutely terrible!! Please give an answer that I can understand(as I like to learn too).....and one also that I can explain to her, so she will understand. I appreciate the help!!!

If an astronomer examines the emission spectrum from luminous hydrogen gas that is moving away from he Earth at a high speed and compares it to a spectrum of hydrogen seen in a laboratory on Earth, what would be different about the frequencies of aspectral lines from the two sources?

I don't have any clue as to the answer. Thanks again guys!

2. Relevant equations

3. The attempt at a solution

2. Apr 24, 2007

Can anyone help me with this.....I just plain and simple do NOT understand it well enough to explain it to her.

Or possibly you could show me a website where I could read up on the material, and try to learn the answer....??.....

3. Apr 24, 2007

### drpizza

You'll want to research redshift and blueshift; google should suffice to find some decent sources.

4. Apr 24, 2007

### Dick

5. Apr 24, 2007

Ok, well I've searched basically both of those things.

I came up with this conclusion:

Due to the fact that the spectrum is moving AWAY from the Earth, it will cause a "redshift". This redshift, increases wavelength which also corresponds to a decrease in the frequency of the electromagnetic radiation.

Is that correct? Also, is that correct with the hydrogen gas(or does the gas not really matter, in this case)?

So basically, I guess I'm saying that the one going away from earth will have a lower frequency than the one observed in the lab.

6. Apr 24, 2007

### Dick

Yes, that's correct. And the fact it's hydrogen doesn't really matter.