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Name: Kurt
Status: other
Grade: other
Location: CA
Country: Austria
Date: Winter 2011-2912

How do we compensate for stars,galaxies, clusters of galaxies, which possibly are covered up in the line of sight?

Dear Kurt,

This is very rare since space is so big. However when a galaxy is in the way, the more distant object can be viewed anyway because the intervening galaxy acts as a gravitational lens that allows us to see the more distant object. Good question.

Sincerely. David H. Levy


There are a couple of issues here: (1) the galactic census is a very rough estimate of the number of galaxies in the universe, so that if we say that there are 200,000 galaxies - that is probably +/- 50,000 and (2) since the Earth traverses quite a distance around the Sun, very few galaxies remain occluded by other galaxies. I think, the galactic census was done primarily to get an idea if gravitational forces from galactic matter alone could explain the expansion of the universe and not to get a real count of the number of galaxies - and since we have found that the number falls far short to explain the rate of expansion, we did not need to get a truly accurate count.

Greg (Roberto Gregorius) Canisius College

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