Mercury, Jupiter and Saturn are currently clustered together in the night sky.
Monday is the last night where the three planets will be lined up and visible at dusk. They seemed the closest they had been to more than two decades on Sunday, forming an equilateral triangle.
“This shape is just a cut in time,” Amy Oliver, a spokeswoman for the Harvard-Smithsonian Center for Astrophysics, told the Boston Globe. “We can not see it exactly like this ever again, as it probably will not happen again in exactly the same way – at least not in your lifetime.”
An astronomical event in which celestial bodies are aligned like this is called a context. A triple lineup like this is known as a planetary trio.
If you hold your palm up against the sky and all three planets are clustered within a circle that fits into the space between your ring finger and your index finger, it̵
This is how you see the planetary trio before it’s gone.
Go out at dusk and bring binoculars
On Mondays, take out at dusk between half an hour and 45 minutes after sunset. Look at the southwest sky. The clearer the sky is and the danger from city lights you are, the easier it will be to see the connection.
Jupiter will look brightest with the naked eye (it is about 10 times brighter than Saturn) followed by Mercury and then Saturn.
Since Saturn is so faint, it may not be distinguishable 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 close to the top, and then aim a pair of binoculars at it. Mercury and Saturn will appear in the same binocular field as Jupiter, according to EarthSky.
After Monday, Jupiter and Saturn dip below the horizon and are no longer visible, while Mercury continues to rise in the sky night after night – moving steadily away from the other two planets.
Although the three worlds almost seem to touch the planetary trio, Jupiter and Saturn are actually separated by almost five times the distance between Earth and the sun. Mercury and Saturn are separated by almost twice as long.
The last time these 3 planets aligned so closely together was in 2000
Astronomers turned their telescopes into the sky last month to capture yet another coherence event as Jupiter and Saturn adjusted closer than they had done for centuries.
In the last 2,000 years, Jupiter and Saturn have only twice come closer to the sky: one was in 1623, but the glare of the sun made it impossible to see. The second was in 1226.
Planetary trios, on the other hand, are far more common. The last one 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.