Science

Venus and Jupiter Planetary Conjunction: What It Is and How to See It

Venus and Jupiter will rendezvous this weekend, with the two bright planets appearing to pass close to each other in what astronomers call a planetary conjunction.

The planets will appear nearest one another on Saturday, April 30, at 3 pm Eastern time. Since it will be very difficult to see the conjunction in daylight, the morning before or after that moment—on April 30 or Sunday, May 1—are your best chances to see Venus and Jupiter seem to nearly collide, according to the National Aeronautics and Space Administration. After Sunday, the planets will look like they’re moving apart.

“Of all the conjunctions between planets, Venus-Jupiter ones are the best from the standpoint that both planets are bright and easy to see even from a city,” said Patrick Hartigan, a professor of physics and astronomy at Rice University in Houston.

At their closest moment in this weekend’s conjunction, Venus and Jupiter will appear as two bright, non-twinkling points of light—Venus is the one that’s a bit brighter—separated by less than half a degree, or about the diameter of a full moon . “At their closest, if you put up your pinkie at arm’s length, you’ll be able to cover them both” as you gaze up at the sky, said NASA astronomer Henry Throop.

The last time the planets were about this close was August 2016; that conjunction was harder to see because the planets were closer to the sun.

Despite their visual proximity during the conjunction, Venus and Jupiter are on average separated by about 416 million miles, or nearly five times the distance between Earth and the sun. Venus will be about 90 million miles from Earth on Saturday, Jupiter more than five times that far.

The illusion stems from the fact that all the planets circle the sun in the same plane but have widely separated orbits, following similar paths through Earth’s sky.

“Think of the planets as horses going around a racetrack,” said Dr. Throop. “Sometimes one horse will overtake another, and that’s when we see a conjunction.

“Venus is the fast horse on the inside lane, and it’s catching up with slow-moving Jupiter and overtaking it in the sky,” he added.

To see the conjunction in the Northern Hemisphere, head outside just before dawn on Saturday or Sunday and look low on the horizon to the southeast. “You have to observe in the hour or so before it gets too light out to see Jupiter,” Dr. Hartigan said. “Too early though, and the objects won’t have risen yet.”

Viewers in the Southern Hemisphere can also see the conjunction in those predawn hours, but the planets will appear more to the east.

Barring cloudy weather, the conjunction should be visible with the naked eye, Dr. Throop said. But binoculars, a telescope or a telephoto lens might enable you to see not just Venus and Jupiter but also Jupiter’s four brightest moons, known as the Galilean moons because they were first observed in 1610 by Galileo.

Conjunctions can involve stars and the moon as well as planets, and they aren’t especially rare. Venus and Jupiter, for example, typically have one conjunction every 13 months or so, according to Dr. Hartigan, though not all of these meetups are easily visible from Earth.

There’s no hard and fast rule among astronomers for how close celestial bodies need to appear in the sky before they are said to be in conjunction. “You can have a conjunction where they get very close, like this one, or even pass directly in front of each other, which is very rare,” Dr. Throop said. “Or you could have a conjunction where they are distant—a couple of degrees apart.”

If you miss this weekend’s celestial show, next April will bring another Venus-Jupiter conjunction, Dr. Hartigan said. “A lot of people might like the one next spring even better—about the same separation, a bit higher up in the sky, and in the evening right after sunset,” he added.

Write to Aylin Woodward at Aylin.Woodward@wsj.com

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