Newsletter Archive

A Slow Reshuffling of Planets

January 6, 2021


Happy New Year!

January 2021 is going to be a fairly calm month, astronomically speaking, with no major events. Relax and enjoy the sunrises and sunsets as the planets slowly rearrange themselves, and enjoy the brilliant raft of constellations decorating the eastern and southern evening skies.

I'll describe the constellations in more detail later this month, after they have risen a little higher, but if you want maps to help you start exploring, may I suggest my Orion and Friends and Winter Hexagon worksheets?

As for the planets, Venus is still gradually sinking into the sunrise, and will continue to do so through February and into March. The Jupiter-Saturn duo will continue to sink into the sunset, and will disappear before this month is out. We will see these various planets swap their sunrise-sunset positions within the next couple of months, but the first step of this planetary reshuffling will occur in a few days, with the reappearance of Mercury. You may recall that Mercury appeared with Venus over the sunrise in November, but sank out of sight in December. It will be reborn in the evening skies very shortly, joining Jupiter and Saturn low over the sunset this weekend.

The Jupiter-Saturn-Mercury trio will be a challenge to find—you will need a clear view of the southwestern horizon, and good timing. Go outdoors this weekend about a half-hour after sunset, and face southwest, and you may see something like this:

Jupiter, Mercury, and Saturn in the Evening Skies

This represents the view from Iowa this Saturday the 9th, at about 5:20 or 5:30 PM. Timing is important here—if you go out too early, the sky will be too bright, and if you go out too late, the planets will be too low to see, and the window between these two limits is quite narrow. And depending on your exact location and time zone, your best time could be different from those I gave by as much as half an hour, so start looking early. Jupiter will be highest and brightest, so look for it first, then look for Mercury, and finally Saturn, which will be quite dim. After this weekend, Saturn will also be the lowest of the three planets. This triplet of planets will be visible together in the sunset for a couple of days, but Saturn will soon disappear, and speedy Mercury will rise rapidly and each day it will noticeably change its position compared to the others. (This "wandering star" was named after the fleet-footed messenger god, because it moves around in the sky so quickly. In this way it is the opposite of nearby Saturn, which was named after Chronos, the god of time. This weekend, the fastest "wandering star" and the slowest "wandering star" will appear next to each other in the sky.)

After this weekend, Jupiter and Saturn will continue to sink into the sunset, and will soon disappear. Look for them to reappear over the sunrises in the middle of February. Mercury will continue to climb higher over the sunset, but will hastily turn around and disappear back into the sunset. The day of "greatest elongation"—meaning the greatest distance from the sun in the sky, and approximately the day when it is highest over the sunset—will be the 23rd of January, and Mercury will be back over the sunrise before February is done.

While the planets rearrange themselves, the moon will continue to zip along the zodiac. It will be New next Tuesday, the 12th, which means it will be a beautiful sunrise crescent with Venus for a few days before this, and it will be a beautiful sunset crescent alongside Jupiter, Saturn, and Mercury for a few days after this. (I think Saturn will be too low and too dim to find by the time the moon joins the scene, but you may still be able to see the Moon with Mercury and Jupiter in the evenings late next week.)

Mars is still there in the evening sky, but it, too, is gradually creeping closer to the sun. It was at "opposition"—meaning opposite to the sun—in October, and by the end of January it will have moved a quarter of the way around. It will then be at "quadrature", meaning a quarter-turn from the sun. In other words, Mars will be high in the south in the evening skies for all of January.

So here is your early January sky-watching assignment: Find a place with a clear view of the southwestern horizon, find the trio of evening planets a half-hour after sunset this Saturday the 9th, and then watch again around the 13th-15th for the crescent moon to join the scene.