While the Earth certainly isn't flat, we can say with confidence that the solar system is. Just look up in the sky for proof. The planets, sun and moon all circle the heavens on essentially the same path — called the ecliptic — through the same dozen constellations of the zodiac. They do this year after year, century after century. If you could literally get above it all and look down, the orbiting planets would remind you of runners assigned to lanes at a track event. All run on the same flat track.

The planets race around the sun in their "lanes", each traveling at their own rate of speed. Not to scale. (NASA)
The planets race around the sun in their "lanes", each traveling at their own rate of speed. Not to scale. (NASA)

Because Earth is one of those runners, when we look off at our fellow planets in the distance we occasionally see them along the same line of sight — one nearer, the other farther away. They may even appear to "touch" as one passes the other. These brief, line-of-sight pairings of planets are called conjunctions., and they're some of the most beautiful sights in the sky.

The top image shows how the moon weaves a short distance above and below the ecliptic during the month. This is caused by its orbit (lower image) which is inclined 5.1° to the Earth's orbit. (Top: Stellarium; bottom: National Solar Observatory)
The top image shows how the moon weaves a short distance above and below the ecliptic during the month. This is caused by its orbit (lower image) which is inclined 5.1° to the Earth's orbit. (Top: Stellarium; bottom: National Solar Observatory)

The moon's path is slightly different. Its orbit is tipped 5.1° relative to the Earth's orbit. As it circles the planet, it weaves a little above and below the ecliptic like a car weaving on a freeway. But it still "keeps with the flow" and minds the ecliptic. Being much closer to us, the moon circles through all the zodiac constellations in just under a month. That means it's in conjunction with every planet in the sky every month. But because it weaves, the separation between moon and planet varies at each conjunction. To be fair, the solar system isn't exactly flat either. Each planet's orbit is slightly tilted in relation to the Earth's. This also contributes to the uniqueness of each alignment..

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The most dramatic conjunctions are the close ones, when the moon shines right next to a bright planet like Venus or Jupiter. One look and you're mesmerized. Venus and the moon undergo 12 conjunctions in 2021, but the best by far will occur Wednesday evening, May 12. Don't miss it!

The slender moon, just 1.5 days old, stops by Venus on May 12 and then by Mercury on the 13th. (Stellarium)
The slender moon, just 1.5 days old, stops by Venus on May 12 and then by Mercury on the 13th. (Stellarium)

Find a location with an unobstructed view to the northwest. The viewing window is brief — only about 25 minutes. Start looking for the thin crescent 20 minutes after the sun sets. Once you've spotted it, gleaming Venus lies just 1° or two moon-diameters to its right. To make sure you're on time, use this calculator to find out when the sun sets for your city.

Observers in the Eastern Time Zone will see the moon and Venus paired up a little closer at 0.8°, while in California, where the sun sets two hours after it does in New York, 1.5° will separate them. Their changing separation is caused by the moon, which is always on the move. By the time the sky gets dark on the West Coast, it will have nearly doubled its apparent distance from Venus.

Over the course of 24 hours, the moon travels 13° up and away from the sun, equal to a little more than a clenched fist held at arm's length. The very next evening, May 13, it leaves Venus behind to find a new companion in Mercury. Mercury is fainter than Venus, and their separation will be larger, around 3°. Though a less dramatic pairing, it's a gift in disguise. Finding Mercury couldn't be easier!

Resolution is a problem when photographing the moon and planets with just a cellphone. A better solution is to mount a pair of binoculars on a tripod and hold the phone up to one of the binocular eyepieces. That's what Argentine amateur astronomer Piqui Diaz did during a conjunction of the crescent moon and Saturn. (Piqui Diaz)
Resolution is a problem when photographing the moon and planets with just a cellphone. A better solution is to mount a pair of binoculars on a tripod and hold the phone up to one of the binocular eyepieces. That's what Argentine amateur astronomer Piqui Diaz did during a conjunction of the crescent moon and Saturn. (Piqui Diaz)

Although mobile phones aren't generally the best cameras for astrophotography there you'll have enough light to capture a pretty scene of the Venus-moon conjunction. Find a cool setting and fire away. If you have a DSLR you can experiment with different focal length lenses to zoom in or "go wide." Set your ISO to 400, the lens to f/4 (or thereabouts) and start with an exposure around 1/125th or 1/60th of a second. As it gets darker out, increase your exposure time will increase. Make sure you focus sharply on the moon before taking pictures.

Clear skies and joyous sights!

"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.