How Many Photons Reach the Hubble Telescope from a Distant Star in a Day?

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Buckethead
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Just for fun I wondered about how many photons hit the Hubble telescope from a single star 13 billion LY away during a one day time exposure and came up with about 40 billion photons. Considering that a single star radiates light in all directions to a radius of 13 billion LY, it puts a perspective on just how many photons are out there. I'm not going to reveal how I came up with this number as I'll get laughed out of the forum :wink:. Anyone else care to come up with a number?
 
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2000 for a star 13 million LY away. With billions, ~1 photon/year.
 

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