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Suppose we have a variable star with a change in magnitude between maximum and minimum of 5 mag.

How much would you need to stop down a telescope (block some of the area) so that the star at maximum brightness appears to be the same brightness as when it is at minimum magnitude with no stop.

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  • $\begingroup$ I'm not sure exactly what you're asking here. Variable stars don't change position, and stars appear as points of light, not disks, even to the strongest telescopes. $\endgroup$
    – user21
    Aug 27, 2017 at 15:24
  • $\begingroup$ I think the question is this: how much would you need to stop down a telescope (block some of the area) so that the star at maximum brightness appears to be the same brightness as when it is at minimum magnitude with no stop. Since the OP has not replied, I assume that his homework is past due :-) $\endgroup$
    – JohnHoltz
    Aug 28, 2017 at 22:04
  • $\begingroup$ Yes that's exactly the question. I apologise for not conveying the meaning of it. I did a rough translation of the question. And actually no,it's not a due homework. I found it on a past paper. $\endgroup$ Aug 28, 2017 at 22:05

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Treating as a school question

Each change of 1 magnitude changes brightness by how much? So by what factor will a change of 5 magnitudes give? (5 magnitudes is a very convenient number for this question)

You will need to reduce the area of the telescope by the same factor.

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