The Moon passes closest to Venus
on January 31 at 17 hours Universal Time, and closest to Mars about 10 hours later (Feb. 1, 2:30 UT).
So the circle embracing the three of them shrinks to its smallest diameter (5.45°) at 22 UT, which is 10 PM in Europe. For America that moment falls in daylight (4 PM EST, 2 PM PST) but after dark the Moon-centered triangle is scarcely different.
The Moon at this time is about 59 Earth-radii away (376,000 kilometers), Venus 0.54 astronomical units or Earth-Sun distances (80,781,000 km), and Mars 1.85 a.u. (276,756,000 km).
As for their brightness, by the way we measure it in astronomy the “magnitudes” of Moon, Venus, and Mars are -8, -4.6, and +1.1. So you might think that Venus is a good deal above the middle – nearer in brightness to the Moon than it is to Mars. I’m not sure it really looks that way; this may be a subjective matter. Each step of magnitude means about 2.5 times more light, and it may be that the upper steps seem to increase a body’s brightness more noticeably. The steps between stars of magnitude 4 and 5 don’t seem as great as those between planets of -1 and -2. Or what do you think?
In our picture of the scene, the Moon is exaggerated 4 times in size, and Venus 150 times so as to show the crescent shape your telescope would find it to have.
(Look closely and you should see a dot: it’s at only 15 – instead of 150 – times Venus’s true size!)
Moon and Venus have similar crescent shapes (of vastly different sizes) because they have arrived at similar angles in relation to us and the Sun. But they have arrived that way by moving in opposing directions: Venus is curving toward us, around and in, to pass between us and the Sun: the Moon is curving out around us from its New toward its First Quarter direction. So from their present positions the Moon will depart rapidly leftward, and Venus rightward, not so rapidly, though rapidly compared with the motions of the more distant planets.
You could take another look at Venus’s motion in the spatial picture with yesterday’s post.