Mercury, Jupiter and Saturn are currently gathering together in the night sky.
Monday is the last night in which the three planets will be arranged and visible at dusk. They appeared for more than two decades on Sunday, forming an equilateral triangle.
“This form is just a change of time,” Amy Oliver, a spokeswoman for the Harvard-Smithsonian Center for Astrophysics, told the Boston Globe. “We’ll never see it that way, because it probably won’t happen the same way – at least not for the rest of your life.”
An astronomical event in which celestial bodies are aligned in this way is called a conjunction. A triple arrangement like this is known as a planetary trio.
If you hold your palm to the sky and the three planets gather in a circle that fits in the space between the nameless and the index finger, this is a trio.
Here’s how to see the planetary trio before it disappears.
Head into the twilight and bring binoculars
On Monday, head to dusk, between half an hour and 45 minutes after sunset. Look at the southwest sky. The clearer the sky and you are the father of the city lights, the easier it will be to see the connection.
Jupiter will appear brightest to the naked eye (about 10 times brighter than Saturn), followed by Mercury, then Saturn.
Because Saturn is so dim, it can be no different from the following sunlight with the naked eye. So the best way to spot a planetary triangle is to focus your gaze on Jupiter, which will be close to the top, and then point the binoculars at it. Mercury and Saturn must appear in the same binocular field as Jupiter, according to EarthSky.
After Monday, Jupiter and Saturn will sink below the horizon and will no longer be seen, while Mercury will continue to rise in the sky night after night – constantly moving away from the other two planets.
Although the three worlds seem to almost touch during the planetary trio, Jupiter and Saturn are actually separated by almost five times the distance between the Earth and the Sun. Mercury and Saturn are separated by almost twice the distance.
The last time these 3 planets aligned so closely was in 2000
Astronomers turned their telescopes to the sky last month to capture another event when Jupiter and Saturn aligned more closely than they had over the centuries.
There have been only two times in the last 2,000 years when Jupiter and Saturn have approached in the sky: One was in 1623, but the glare of the sun made it impossible to see. The other was in 1226.
On the other hand, planetary trios are much more common. The last was in October 2015. Another trio, including Mercury, Venus and Jupiter, will take place on February 13, according to EarthSky.
Mercury, Jupiter and Saturn last formed a triangle in May 2000.
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