Mercury reaches on Monday January 30 its westernmost elongation, that is, its farthest out from the Sun in the morning sky.
See the end note about enlarging illustrations.
The little planet is shining at magnitude -0.1, like some of the brightest stars. But it is, at the time and location of our picture, only 7° above the horizon.
This is the year’s most favorable morning appearance of Mercury for north-hemisphere observers, but it is much better for the southern hemisphere; and there will be a better chance to see Mercury in the evening sky around April 11.
All this is made clear by our graph comparing Mercury’s apparitions, on page 106 of Astronomical Calendar 2023
in which the gray areas are evening and the blue are morning excursions. The top figures are the maximum elongations, reached at the top dates shown beneath. Curves show the altitude of the planet above the horizon at sunrise or sunset, for latitude 40° north (thick line) and 35° south (thin), with maxima reached at the parenthesized dates below (40° north bold).
On the other side of the Sun, in the evening sky, during the night of Jan. 30-31, the Moon passes close enough south of Mars that it hides it – an occultation.
The track of the Moon’s “Mars shadow,” from within which the occultation can be seen, passes across the Pacific and the waist of the Americas.
If you are in the southern U.S.A., Mexico, central America, or northeastern South America, you can watch the occultation, which centers around 5 Universal Time (midnight by clocks in North America’s Eastern time zone, 11 PM on Jan. 30 in the Central zone, and so on). The nearer you are to the middle of the occultation band, the longer before this the occultation will start.
The Moon is only a few days before full, and about 19,000 times brighter than Mars. It’s the slender dark side of the Moon that approaches the planet, so the disappearance may come unexpectedly.
Here is the scene at midnight between Jan. 30 and 31, for the American location we usually use – longitude 90° west, latitude 40° north..
But that latitude is north of the band of occultation, so that the Moon is seen to pass just clear south of Mars. From somewhat farther south, along the northern limit of the band, you would see a grazing occultation – Mars even blinking in and out behind mountains on the Moon’s limb (apparent edge).
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