Mercury, Jupiter and Saturn come together in the night sky in a rare conjunction event on three planets. Here’s how to see it on Monday.

Mercury, Jupiter and Saturn currently cluster together in the night sky.

Monday is the last night the three planets will be aligned and visible at dusk. They looked the closest they had been in more than two decades on Sunday, forming an equilateral triangle.

“This shape is just a leap in time,” Amy Oliver, a spokesperson for the Harvard-Smithsonian Center for Astrophysics, told the Boston Globe. “We’ll never see it exactly like that again, because it probably won’t happen the same way – at least not in your lifetime.”

An astronomical event in which the heavenly bodies align like this is called a conjunction. A triple alignment like this is known as a planetary trio.

If you hold your palm up to the sky and the three planets cluster together in a circle that fits into the space between your ring finger and index finger, it’s a trio.

Here’s how to see the planetary trio before they vanish.

Go out at dusk and bring binoculars

On Mondays, set off at dusk, between half an hour and 45 minutes after sunset. Look at the sky from the southwest. The clearer the sky and the father of city lights that you are, the easier it will be to see the conjunction.

Jupiter will look the brightest to the naked eye (it’s about 10 times brighter than Saturn), followed by Mercury, then Saturn.

Since Saturn is so dark, it may not be distinguished from the afterglow of the sun with the naked eye. So the best way to spot the planetary triangle is to focus your eyes on Jupiter, which will be near the top, and then point a pair of binoculars at it. Mercury and Saturn are expected to appear in the same binocular field as Jupiter, according to EarthSky.

The story continues

After Monday, Jupiter and Saturn will dive below the horizon and no longer be visible, while Mercury will continue to rise in the sky night after night – steadily moving away from the other two planets.

Although the three worlds seem to almost touch during the planetary trio, Jupiter and Saturn are actually nearly five times the distance between Earth and the sun. Mercury and Saturn are almost twice this distance apart.

The last time these 3 planets aligned so closely was in 2000

Astronomers turned their telescopes skyward last month to catch another conjunction event, when Jupiter and Saturn aligned more closely than they had for centuries.

In the past 2,000 years, there have only been two times that Jupiter and Saturn have come close in the sky: one was in 1623, but the sun’s glare made sight impossible. The other was in 1226.

Planetary trios, on the other hand, are much more common. The last was in October 2015. Another trio, involving Mercury, Venus and Jupiter, will take place on February 13, according to EarthSky.

The last time Mercury, Jupiter, and Saturn formed a triangle was in May 2000.

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