Physics question....

Question

This is completely unrelated to Spanish (I know!!), but I could do with some help.....

The question is: In a particular binary star system, star A has apparent brightness 8.0 mutiplied by 10 to the power -13 and star B has apparent brightness 2.0 x 10 to the power -14. The surface area of star B is 10,000 times smaller than that of star A. Calculate the ratio:

Surface temp of star B / Surface temp of star A

I know that I should use the formula L= stefan-boltzmann constant multiplied by Area by temperature to the power 4. My problem is though, the value of luminosity can only be figured out with a value of the distance.

So what can I do?

Pay attention in class next time! - Sabor, Dec 16, 2010

No, I understand what I'm being taught.....I just need help with this particular question!! - Seb79, Dec 16, 2010

Answer 1

Of course, this is not homework. This is dinner conversation. I pose such questions to my children routinely during dinner.

This is hard to explain without being able to write the equeations which are too hard in this editor.

Follow these steps.

K=stefan-boltzman constant

create the two equations for L(A) for star A; L(B) for star B

They should be in the format of some number (8x10-13/K)=area(A) xT(A) to the 4th power.

L(B)= different number=2x10-14/k=area(A)/10,000xT(B) to the 4th power

solve for (area A)

• some number x area(A)=t(A)to the 4th

• diff. number x area(A)=t(B)to the 4th

• do math to get area(A)=T(A)to 4th/some number and

• area (A)=t(B) to 4th/diff no.

therefore,

T(A)to 4th/T(B)to 4th=some other number That is your ratio.

I didn't say that it wasn't homework!! I appreciate your sarcasm and quite blunt statement, but I just wanted some help, that's all. Is that too much to ask? - Seb79, Dec 16, 2010

Thank you....it's just that to be honest, I was just kind of getting annoyed at the responses. But thanks a lot for your time!! :) - Seb79, Dec 16, 2010

Come on, Seb, really... If you're dealing with that sort of math, one surmises you're a reasonably smart fellow, yes? What did you expect, posting a question like that in a Spanish Forum? Fortunetly for you, we do have a number of very bright fellows... - Gekkosan, Dec 16, 2010

...on board, who also don't mind getting off-topic to give a hand. I reckon you should be thankful for that, and the fact that you didn't get meaner responses! ;-) - Gekkosan, Dec 16, 2010

Chill out Seb - Q's just messing with you ;) - patch, Dec 16, 2010

Answer 2

I recommend changing majors. Sociology never has questions like this.

Many social science majors are terrified of numbers. People had nervous break downs in every statistics class I ever took. - Leatha, Dec 17, 2010

Fear of numbers is nothing more than a fear of life. Embrace the numerical and life will become full, focus on 3, 7, & 12 and life will become nearly full. - djnotsophat, Dec 19, 2010

Answer 3

Sure seems like something is missing. How about adding an equation that relates apparent luminosity to distance and absolute luminosity? That additional constraint may be all you need. Good luck!

Answer 4

Fortunately my 3rd grader is home from school due to bad winter strom. I'll ask him; be back in a sec....

Answer 5

Apparently astronomy makes people grumpy. I'm glad I stay away from that sort of thing.

Estoy contigo cien por ciento Leatha! - galsally, Dec 24, 2010

Answer 6

And to think I only took the introductory astronomy course thinking it would be enough to see me through the rest of my life!

Answer 7

-

Answer 8

I don't think a distance is needed. Adding this to kick the thread back up the list. Look at my amended answer.

Answer 9

I would simply appreciate a pointer in the right direction!! I'm sorry if I've somewhat offended you in any shape or form....and I won't make that mistake of offending you again.

Sorry.

I edited my answer. You might want to look at it. - 0074b507, Dec 16, 2010

Answer 10

For the apparent luminosity you need the distance, if I'm not mistaken. For luminosity, however, you can use L = 4 ? R^2 ? T^4, so rearranging for T and getting the ratio of the two you get the root four of ((L1 R2^2) / (L2 R1^2)). Using the data provided, L1/L2 = 0.025 and R2^2/R1^2 is the ratio between the surfaces, i.e.10,000. So you get the root four of 250, which is about 3.98.

Maybe you can use Mediterrunio's suggestion and get the same arbitrary distance for both stars. The ratio is likely to cancel this value anyway.

Just a suggestion. I'm not an expert in astronomy.

Thank you...I really appreciate it. - Seb79, Dec 16, 2010

Answer 11

please, Be clear and provide context next time.

Why don´t you suppose an arbitrary distance, since it is not given data.

Ok, I will be clearer next time...thank you. - Seb79, Dec 16, 2010

Answer 12

delete=server double posted

Answer 13

-