As the Memorial Day Weekend takes shape, find a fun planetary triangle in the west-northwestern sky at dusk.
Thanks to celestial mechanics and our own unique, earthly perspective on the cosmos, the effervescent Venus, giant Jupiter and the fleet Mercury create a noticeable triangular for the next week. However, that triangular shape soon gives way to grammar school-style, single-file cosmic lunch line.
Noted retired NASA astronomer Fred Espenak explains this triple planetary alignment: “At the climax of this celestial grouping, the brilliant planets Jupiter and Venus will be joined by fainter Mercury to form a tight nearly equilateral triangle,” he says.
Look to the west-northwestern sky after dusk – in the direction to where the sun has just set – and you’ll see the bright Venus and Jupiter loitering low in the sky. The planets emerge, as the sky gets darker, at about 40 minutes after sunset.
For the past several weeks Jupiter and Venus have been approaching each other like slow-motion lovers running on a grassy knoll.
On Friday May 24 you’ll find the bright Venus (-3.9 magnitude, very bright) is closest to the horizon, while Jupiter (-1.9 bright magnitude, bright) is to Venus’ upper left. Mercury (-1.3 magnitude, bright, but still dimmer than Jupiter) is to Venus’ right. By Saturday May 25 evening twilight, Mercury moves a smidgen away from Venus and is now located to Venus’ upper right.
Espenak has created sky charts to see the fine-tuned changes occurring each night.
You’ll notice after sunset on Sunday May 26 that Jupiter and Venus have moved closer in the sky, but Mercury climbs a little higher. Keep in mind that Venus is the brightest and Mercury remains the dimmest.
Espenak reminds us that during this breathtaking triple alignment, the planets are not really next to each other. The actual planetary distances from Earth vary widely: the gaseous Jupiter is 564 million miles from us, while Venus sits at 152 million miles away. The quick Mercury, 105 million miles.
Jupiter provides a cosmic snuggle for Venus on the evening of Memorial Day, as Mercury climbs higher. On Tuesday May 28, Venus passes one degree north of Jupiter, and the two bright planets will be three degrees below fainter Mercury, says astronomer Geoff Chester of the U.S. Naval Observatory in his blog The Sky This Week.
For May 29- June 1, the triangle morphs out of the triangle and a cosmic straight line emerges. The highest planet Mercury, then Venus and Jupiter straighten out – and then stretch out. And then Jupiter – on successive days – fall into the sun’s glare.
Sky Telescope Magazine provides a very good animation:
To read more, Sky and Telescope features an article by senior editor Alan MacRobert and associate editor Tony Flanders: Watch Three Planets Dancing in Twilight
StarDate Magazine, from the University of Texas, provides a fast video animation of the alignment: