Massachusetts: Every eight years, the brightest planet and the best-known open cluster come together — sometimes they’re a bit farther apart, sometimes they’re closer together.
This year is a good one for viewers in North America: Venus will pass a mere 1/4 degree south of Alcyone, the brightest star in the cluster. For viewers farther east, the planet will brush by Merope, instead.
Venus and Earth are in what’s a called a near resonance. As a result, Earth and Venus return to nearly the same positions in their orbits at eight-year intervals, which is why we get an event like this Friday’s infrequently.
In fact, Venus visits the Pleiades’ neighborhood often, but it’s only once every eight years that the planet strolls right through the cluster. Since the orbital paths of Venus and Earth are elliptical and not perfect circles, this resonance effect is imprecise.
In addition, Venus’s orbit is tilted with respect to Earth’s path around the Sun by 3.4 degrees, which results in slightly different albeit similar passages every eight years.
Venus currently blazes at magnitude -4.6 so you can’t miss it (it’s almost 20 times brighter than Sirius, the night sky’s brightest star). Looking toward the sunset direction and halfway up the western sky during evening twilight, and the brightest object will be the planet. As the sky darkens, more and more Pleiades cluster members will start appearing.
People can see them without optical aid, but binoculars will greatly enhance the view. Those who have access to a small telescope with a wide-field eyepiece should see Venus as a tiny, fat illuminated crescent.
“Don’t despair if the weather forecast is dismal for your location this coming Friday,” said Diana Hannikainen, Sky & Telescope’s Observing Editor.
“During several evenings before and several evenings after the event, Venus is still pretty close to the Pleiades and will make for a delightful scene nevertheless. So, go outside, starting tonight, and look up,” Diana added.
In fact, Venus will remain within 5 degrees of the cluster through April 9th.
The event will also be live-streamed at Gianluca Masi’s Virtual Telescope site starting at 1:30 p.m. Eastern Daylight Time (17:30 UT).