A density of meetings

Tomorrow morning the Moon will finish its plunge past a bright star and three bright planets by gliding less than a degree from little Mercury.


I am being tweetly coached to make not just blog posts but Tweets, so I broke off what I was doing and made this picture and used it that way. But the event is more interesting than can be expressed in 140 characters.

Only an hour before the conjunction with Mercury, the Moon is at its ascending node. That is, it slides northward across the ecliptic, as you may be able to see in the picture. The point at which it does so happens to be only 1 degree past that cardinal point in the sky where the ecliptic itself slides southward through the celestial equator (it’s the point where the Sun was at the autumn equinox).

Furthermore, only one hour after its conjunction with Mercury the Moon arrives at its apogee, its most distant from us.

11 UT (=7 EDT): Moon at ascending node (at longitude 181 degrees).
12 UT: Moon 0.9 degree south of Mercury. (They are 17 degrees from the Sun.)
13 UT: Moon at apogee (63.7 Earth-radii from the center of the Earth – second greatest distance in the year, after Sep. 14).

A sky may be bare, especially a sky washed over by growing twilight, but it may contain a spot of concentration, rather like a dense city on the map of a desert country.


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