When were most of the moon's craters formed, and how big is crater Copernicus?

>When were most of the moons craters formed?
>how big is the copernicus crater.

Most of the craters on the moon were formed around 4 billion years
ago, soon after the Moon and the Earth solidified. Back then we
believe the solar system was full of leftover bits of rock and ice
that hadn't yet been incorporated into planets. The rate of meteorite
strikes was much, much higher than it is today.

To answer your second question I used the Alta Vista search engine,
http://www.altavista.digital.com, to look for web pages containing
all four of the words "crater", "copernicus", "diameter" and "lunar".
One of the matches is a page at NASA's Goddard Space Flight Center
(GSFC) which has a high-resolution picture of the crater and says it's
100km across.

Best wishes,
-Neal.

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