I already glimpsed this scene out of a train window on the way home.
Because of having to be away all day I have to apologize for telling you about it belatedly.
The Moon passes north of Venus at midnight between Feb. 20 and 21 by Universal Time (midnight in Britain, 7 PM in eastern North America on Feb. 20) and closer north of Mars an hour later.
The smallest circle within which the three fit in the middle of this operation is just under 2 degrees in diameter – but that assumes we mean the center of the Moon, and as seen from the center of the Earth. From an actual northern latitude the Moon appears farther south – as plotted in the picture – so that the tightest circle is even smaller.
If you are out at that time of 0h UT you will be seeing this tightest fit of the three bright bodies. But even a bit later into the twilight, if you are farther west, so long as Venus and Mars are still above the horizon, you’re seeing the pattern tighten in that Venus is drawing closer to Mars, though the Moon is drawing away from them. Tomorrow evening, the Moon will be much farther on, but Venus and Mars even closer to each other. Venus will pass only 0.4 degree south of Mars on Sunday Feb. 22 at 6 UT, so in the evening twilight of Feb. 21 you will see them just before this happens, and on the next evening, just after, with Venus now higher.
This “trio,” or gathering of three bodies (which may include planets, the Moon, or first-magnitude stars) within a circle of less than 5 degrees, is the second of 2015 (after the Moon-Mars-Neptune one of Jan. 23); there are several more, so I hope I get to warn you of them less hastily.