how much moon will be lighted three weeks after a new moon?

Answer 1

One full side of the moon is always lighted. We just can't always see it.

We will be able to see 1/4 of the moon lighted.

Answer 2

What we see as moonlight is sunlight being reflected from the moon. Because the moon rotates around the earth sometimes it's the side of the moon that we don't see which is illuminated (new moon) and sometimes we see the side which is illuminated (full moon).

It takes the moon 29 days to go right round the earth so the cycles repeat themselves ever 29 days. To keep it simple we'll assume it's 28 days (4 weeks).


After a new moon we start to see the moon being illuminated (waxing) and one week after a new moon is what's known as the First Quarter - the typical crescent shaped moon, a week after this is a full moon. After the full moon it begins to go into shadow again (waning) and after a week it's back to being the familiar crescent shape and is what's known as the Last Quarter, this is what you'll see three weeks after a new moon. One week later and it's back to being in darkness and a new moon.