It’s not enough that the dawn planets have captured our attention over the past couple weeks. Now Venus wants to get into the act. In a highly anticipated event — one that occurs only once every 8 years — Venus will pass in front of the iconic Pleiades star cluster. That’s right. It will plow right through the cluster’s southern edge, passing ¼° south of the star Alcyone (al-SY-oh-nee), the brightest of the bunch.
This goes down on Friday, April 3 as soon as the sky gets dark until the duo sets around midnight. To see it just face the sunset direction and look up to find Venus, a brilliant “star” high in the western sky. Depending on how dark it is at the time you’ll see several cluster stars flickering around the gleaming planet like sparks from a fire.
While you don’t necessarily need any equipment to see this gorgeous alignment I highly recommend a pair of 7x or 10x binoculars. The extra light gathering capacity and little bit of magnification will make the cluster pop and Venus dazzle. A small telescope will do the same. Use low magnification — no more than 20x or 30x. Wide-field events like this were made for simple instruments.
Venus last skirted the Pleiades on April 3, 2012 and will again on April 3, 2028. This is no coincidence. Over time, repeated gravitational interactions between the Earth and Venus have brought the two bodies into a near resonance such that for every eight Earth years, Venus circles the Sun almost exactly 13 times. This 8:13 ratio means that the two planets return to nearly the same positions in their orbits at eight-year intervals, and Venus repeats it course across the sky. That also means a repeat performance across the Pleiades. In fact, wherever you happen to see Venus in the sky it will occupy nearly the same spot 8 years later.
I said “nearly.” Venus and Earth orbit in ellipses rather than perfect circles, and Venus’s orbit is inclined 3.4° to the plane Earth’s orbit. This makes for an imperfect resonance and ensures that each Pleiades passage is unique.
Tonight (March 31) the two are separated by 2.5°, an easy fit for any pair of binoculars. They’ll be closest Friday night, but if you’re expecting clouds — like we are here in northern Minnesota — I encourage you to enjoy the sight anytime between now and about April 5th. If you’re really socked in check out Gianluca Masi’s Virtual Telescope site. He’ll livestream the event starting at 12:30 p.m. (17:30 UT) on April 3.
Take a picture while you’re at it. The Pleiades will appear very small, but you can compose passable scene in mid-twilight with even a cell phone. Better, mount a pair of binoculars on a tripod and hold your phone up to one of the eyepieces for a magnified view. Set the ISO to 1600 and expose between 2 and 5 seconds.
If you have a DSLR you can take photos of much higher resolution. Set the lens to M (manual), the shutter speed to M and use the camera’s live view feature (a button on the backside of the camera body) to sharply focus Venus before taking a photo. For starters try ISO 800 or 1600 with the lens wide open at f/2.8 or f/4. Expose anywhere between 2 and 25 seconds. Check the back screen periodically to see if you’re on target and adjust exposure as needed. With a wide-angle lens you can expose longer before stars start to trail. When using a telephoto you will only have a few seconds, so boost your ISO to at least 1600, preferably 3200 or 6400.
Or just forget about the camera and enjoy the sight. Making a cosmic connection provides a needed release in these unnerving times.