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hamid1455

Posted: Sun Oct 20, 2013 3:32 pm Post subject: astronomy question 


I'm reading essential cosmic perspective 6th edition and am stuck on a question while reading about Doppler Shift.
The question gives me 2 wavelengths and asks me to calculate the length of a day on Jupiter.
So far, I've used the Doppler Shift Equation and gotten 24 km/s as the radial velocity. The two wavelengths are: 499.98 nm and 500.02 nm. I'm not quite sure as to what I should do next. I've looked through the useful formula equations section in the book, but I don't see anything I can use.
I'm trying to find out how a length of a day is calculated for Earth, but I don't think it can be used for this question. 





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DemonWasp

Posted: Sun Oct 20, 2013 3:38 pm Post subject: RE:astronomy question 


If you know how fast the "surface" is rotating (I'm assuming that's what "radial velocity" means), and you know the size of the planet, can't you find the length of the day by simple geometry? 





hamid1455

Posted: Sun Oct 20, 2013 3:57 pm Post subject: Re: astronomy question 


well, I'm only supposed to use what's given in the textbook (I can use basic equations learned in math). I do have the radius of the planet, but I don't know the equation of how I am supposed to use the radial velocity. Just now, I tried dividing the diameter by the radial velocity and got the wrong answer (about 1.6 hours).
The question is multiple choice (A: 1 hour, B: 5 hours, C: 10 hours, D: 15 hours, E: 20 hours). 





Insectoid

Posted: Sun Oct 20, 2013 4:11 pm Post subject: RE:astronomy question 


If you have the radius, you can calculate the circumference using basic equations learned in math. That should make this trivial. 





hamid1455

Posted: Sun Oct 20, 2013 4:30 pm Post subject: RE:astronomy question 


So I calculate the circumference and divide it by the radial velocity? I just tried that and still my answer is wrong. Don't know what I am doing incorrectly. 





hamid1455

Posted: Sun Oct 20, 2013 5:33 pm Post subject: RE:astronomy question 


oh woops. I was using the wrong number for the radius. Got the answer. Thanks everyone 





