22 Feb '06 20:38

Star D has a spectral calss of M2, and star E has a spectral class of B8. How many more times energy per unit surface area does one have over the other?

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Account suspended22 Feb '06 20:48

Well if the spectral class of m2 is PIx3 then that would make it 4x greater than the spectral class of*Originally posted by abejnood***Star D has a spectral calss of M2, and star E has a spectral class of B8. How many more times energy per unit surface area does one have over the other?**

b8. So by multiplying the amount of energy per unit would be equal to the amount of the spectral class b8, but still less than the energy given off by, say, M2. The heat factor also comes into consideration which can lower the level of Star D SPECTRAL CLASS M2.- Joined
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Young World23 Feb '06 01:01

No, it was in last years at University of Illinois at Urbana Champain. I don't care about the answer, i already knew it, I just want to know HOW they get 39? I can't figure it out. I got the other problems, just not that one.*Originally posted by Balla88***B8 has about 39 times more. This question was in this year's National Science Olympiad.**- Joined
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rushing to and fro23 Feb '06 02:52

They probably just ask a brainy physicist like Mr. Trains for the answer. Barring that, they might calculate it based on some assumptions about the surface temperature, similar to....*Originally posted by abejnood***No, it was in last years at University of Illinois at Urbana Champain. I don't care about the answer, i already knew it, I just want to know HOW they get 39? I can't figure it out....**

http://en.wikipedia.org/wiki/Stefan-Boltzmann_law- Joined
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Young World23 Feb '06 18:18

Yeah, that's what's the problem with me, too. I can't figure out how they get 39. Why 39? Why not 42? I don't get it 😞*Originally posted by sonhouse***So how do they come up with 39X? I did a quick look at spectral**

types on goo gal but nothing popped up specifically, except the

old O B A F G K M (Oh Be A Fine Girl, Kiss Me) thing I learned in

8th grade.- Joined
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slatington, pa, usa23 Feb '06 21:291 edit

Not 42, thats the answer to EVERYTHING!🙂*Originally posted by abejnood***Yeah, that's what's the problem with me, too. I can't figure out how they get 39. Why 39? Why not 42? I don't get it 😞**

Another thing about the 39 times, it seems a bit low since the two

stars are almost opposite sides of the classes, 25,000 deg.

or so on one side V 4000 ish deg C on the other?- Joined
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p^2.sin(phi)24 Feb '06 01:241 editBetelgeuse is a B8 star. Rigel is a M2 star.

Betelgeuse has a radius of 1.4 au and a luminosity between 40,000 and 100,000 solars.

Rigel has a radius of 65 au and a luminosity around 50,000 solars.

Therefore Betelgeuse has a surface area of 5.5 × 10^17 km^2 and Rigel has a surface area of 1.2 × 10^21 km^2.

Therefore I get 2.2 * 10^3 as the ratio of energy per unit surface area.

No idea how they got that answer.- Joined
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slatington, pa, usa25 Feb '06 16:58

I looked at the data for Rigel and it shows mass of 17 in units called*Originally posted by XanthosNZ***Betelgeuse is a B8 star. Rigel is a M2 star.**

Betelgeuse has a radius of 1.4 au and a luminosity between 40,000 and 100,000 solars.

Rigel has a radius of 65 au and a luminosity around 50,000 solars.

Therefore Betelgeuse has a surface area of 5.5 × 10^17 km^2 and Rigel has a surface area of 1.2 × 10^21 km^2.

Therefore I get 2.2 * 10^3 as the ratio of energy per unit surface area.

No idea how they got that answer.

M with a square O subscript, could not find the exact meaning but I

suspect it means 17 times of Sol and the size at 60 "R" with the same

subscript. Which I suspect is 60 times the RADIUS if Sol which would

vastly change your numbers. I have heard of big stars, but 65 AU

would make it about 12 BILLION miles across, I think thats patently

impossible. So my guess is its 60 or 65 times 704,000 KM (radius of

sol) or 45 million Km, a more reasonable answer.