Combined apparent magnitude of a star cluster

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velkyr
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Hi all, I've been set a question which asks for the combined apparent magnitude of a cluster of 25000 stars. 1000 of them have an apparent magnitude m = 12.0, and the other 24000 have m = 15.0.

So far I've calculated that the combined apparent magnitude of the set of 1000 stars is exactly 7, and for the 24000 it is approximately 4 (4.04947...). However, I don't know how to then combine these values for the whole cluster.

I've been using the equation:  m_1 - m_2 = 2.5log(L_1/L_2)

Presumably I'll have to use this again, but the issue is I don't actually know how to calculate the luminosity/intensity required... Up until this point, the fractions have just cancelled to simple numbers without a prior calculation being needed. I've tried to search how to progress but nothing is making much sense to me Any help would be much appreciated.
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velkyr
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Surely someone has an idea? Please
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Absent Agent
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(Original post by velkyr)
Hi all, I've been set a question which asks for the combined apparent magnitude of a cluster of 25000 stars. 1000 of them have an apparent magnitude m = 12.0, and the other 24000 have m = 15.0.

So far I've calculated that the combined apparent magnitude of the set of 1000 stars is exactly 7, and for the 24000 it is approximately 4 (4.04947...). However, I don't know how to then combine these values for the whole cluster.

I've been using the equation:  m_1 - m_2 = 2.5log(L_1/L_2)

Presumably I'll have to use this again, but the issue is I don't actually know how to calculate the luminosity/intensity required... Up until this point, the fractions have just cancelled to simple numbers without a prior calculation being needed. I've tried to search how to progress but nothing is making much sense to me Any help would be much appreciated.
I didn't do astrophysics in My A2 units so I really don't know how to approach the question. For what level is this? Is there an equation to calculate the luminosity/intensity? There are some Astrophysics notes online for AQA that might be of help.

Edit: perhaps this helps.

http://physics.unl.edu/~klee/ast204/...-solutions.pdf
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velkyr
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(Original post by Mehrdad jafari)
I didn't do astrophysics in My A2 units so I really don't know how to approach the question. For what level is this? Is there an equation to calculate the luminosity/intensity? There are some Astrophysics notes online for AQA that might be of help.

Edit: perhaps this helps.

http://physics.unl.edu/~klee/ast204/...-solutions.pdf
Hi, it's for first year undergraduate work.

I was using that question to help me through it but I don't know how the last part of it is done. Therein lies my issue.
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velkyr
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Nevermind, have sorted it by using another method now. Thanks anyway.
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Absent Agent
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(Original post by velkyr)
Nevermind, have sorted it by using another method now. Thanks anyway.
No worries! Glad you managed to figure it out as I really have no idea how to work that out.
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