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


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


Replies:
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


Kurt,

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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