This Month's Mars-Mercury Conjunction Will Be The Closest Planetary Meeting This Year

On January 27, Mercury and Mars will pass a fifth of a degree (12 arcminutes) from each other from Earth’s perspective. That will make both easily visible in the same field of view of a backyard telescope, let alone binoculars. However, you will not only need to be an early riser to see them, but to have a good view east or southeast, depending on your location, and willing to make allowances for the twilight. That said, it will be the closest conjunction of the year between planets visible to the naked eye.

The passage of the planets through the sky means the faster movers pass the slower ones quite frequently, forming what is known as a conjunction. If the plane in which the planets orbit was perfectly flat, then every conjunction would see one planet pass directly in front or behind the other. However, while Jupiter has done a good job of mustering its lesser siblings into line, it hasn’t been that good. Deviations from the plane mean that conjunctions can often be several degrees apart, enough to greatly diminish the show.

On the other hand, some rare conjunctions are so close it can be hard to tell the planets apart with the naked eye. In such cases, even small optical instruments reveal a magnificent sight. The 2020 Great Conjunction between Jupiter and Saturn was a particularly memorable experience for those with a telescope. This year, Mars and Mercury won’t look quite as impressive, but they will be almost as close.

The great conjunction took place over more than a week, since Jupiter and Saturn move slowly against the stars and each other. Anything with Mercury involved is much quicker, so if you miss this event, the distance will be a lot greater the next day. The closest approach is at 3:48 pm GMT (11:48 am ET), at which time it will be the middle of the day North America. The best views of the event will be from New Zealand (where it will be seen on the morning of January 28), or Hawai'i. Still, the separation will not be too great for those who see it a few hours off its best.

The event takes place in Sagittarius, which no doubt astrologers will consider very significant in ways we will ignore. Being a southern constellation, however, this means that it will be much easier to see from the Southern Hemisphere.

The planets will be less than 20 degrees east of the Sun, and therefore rising just over an hour earlier.

There will be six other conjunctions between naked-eye planets this year. Some, such as between Venus and Saturn on March 21, will be almost as close. However, not only will the closest of these also be early morning events, but they will be even more affected by predawn light by the time the planets rise.

On the other hand, if you count conjunctions that require optical instruments, Mars and Neptune will be less than a twentieth of a degree apart on April 29.

For those who think the predawn hours are for sleep, or simply lack a handy view east, the Moon has conjunctions of its own with planets (and stars for that matter). Tonight (Thursday), there will be a closer than average conjunction with Jupiter. It will be visible from shortly after sunset until around midnight. The pair won’t be anything like as close as Mars and Mercury (at least two degrees separation), but the brightness of the pair may compensate.

Don’t be too upset if you’re reading this after the chance has been missed. The Moon moves much faster from our perspective than any planet, and it will pass Jupiter again each month. Both the February 15 and March 13 events will be close enough to be impressive, and visible at civilized hours of the night.