Expert: Courtney Seligman - 1/20/2009

Question
What is the term used to describe when the sun and moon are both visible? (I.e. the sun is setting but visible and the moon is also visible?)

Answer
I don't think there is a term to describe that, because it's almost an everyday occurrence (though most people don't notice it).

There are only a few days each month when you can't see both the Sun and Moon, at the same time. These are the days near new moon when the Moon is so nearly in the same direction as the Sun that even though both are up for most of the day, the sky near the Moon is too bright to notice that it's there. The rest of the month, the Moon is visible for part or even most of the day. Starting a few days after new moon, the Moon can be seen to the east of the Sun in the sky, from sometime in the early morning, until sometime after sunset. It's easier to notice it after sunset, because its daylit side brightly contrasts with the night sky; but if you know where to look, you can easily see it for 10 or 11 days out of the 14 or 15 days between new and full moon.

Similarly, you can see the Moon to the west of the Sun on most of the days after full moon. It is only on the day of the full moon, when the Moon rises within half an hour of sunset, that there is very little time that both the Moon and Sun are in the sky. So actually, it's more unusual NOT to be able to see both of them than to be able to see both. On average, out of the 29 1/2 days in a cycle of lunar phases, there are only 6 or 7 days when you can't see the Moon at some time during the day (presuming, of course, that we ignore cloudy weather and such).

Courtney Seligman