Are you ready for a spectacular conjunction in the post-sunset twilight sky?
This weekend, the sparkling Pleiades or “Seven Sisters” will gain an extra “star” to temporarily become the “Eight Sisters” as the best-known open cluster teams-up with the brightest planet.
One of the most beautiful sights in the night sky, this famous open cluster of hot, young blue stars is slowly sinking towards the western horizon in twilight. However, before it disappears for summer there’s one more treat in store as the planet Venus makes a pit-stop in the Pleiades. Although you will be able to see the sight with the naked eye, a great view is assured through any pair of binoculars.
It’s something that happens only once every eight years, and this year is a good one. It will be best seen on the evenings on Friday and Saturday, April 3 and 4, 2020.
What are the Pleiades and why are they special?
The Pleiades are an open cluster of hot B-type stars in the constellation of Taurus that are a mere 100 million years old—a blink of an eye in cosmic terms. Arranged in the shape of a small “Big Dipper,” the Pleiades have seven or eight really bright stars, but over 100 in total.
What makes the Pleiades really special to stargazers is that they are really bright (go find them and you’ll never, ever lose them again) and they’re visible to everyone on the planet for six months of the year.
Why is Venus ‘in’ the Pleiades?
Since late 2019, Venus has been known as the “Evening Star” because it has been rising high above the western horizon each night. It actually reached its highest point above the horizon—its greatest elongation east—on March 24. However, it’s still incredibly high in the sky in the twilight at around 45° above the western horizon.
It’s only a fleeting visit to the Pleiades for Venus because the planet is now appearing to sink back towards the sun. By late May we will not be able to see Venus in the twilight sky, and by June 3, 2020, Venus will be completely lost in the sun’s glare.
Why does it happen every eight years?
Venus and Earth are in what’s called a near resonance, so both return to nearly the same positions in the solar system every eight years. The last close encounter of Venus with the Pleiades was on April 3, 2012.
When to see Venus in the Pleiades
On the nights of Friday and Saturday, April 3 and 4, 2020, Venus will shine a mere 0.3° south of the Pleiades. Look west in the twilight and you’ll see Venus immediately. However, do also look on April 2 and April 5 since Venus will be either side of the cluster.
“Don’t despair if the weather forecast is dismal for your location this coming Friday,” says Diana Hannikainen (pronounced HUHN-ih-ky-nen), 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.” In fact, Venus will remain within 5 degrees of the cluster through April 9.
How to see Venus in the Pleiades
According to Sky & Telescope, look toward the sunset direction and halfway up the western sky during evening twilight, and the brightest object will be Venus. As the sky darkens, more and more Pleiades cluster members will start appearing. You can see them without optical aid, but binoculars will greatly enhance the view. If you have access to a small telescope with a wide-field eyepiece you’ll see Venus as a tiny, fat illuminated crescent.
It promises to be an awesome sight.
How to livestream Venus in the Pleiades
If it’s cloudy on Friday evening you can still watch the event via livestream at Gianluca Masi’s Virtual Telescope site starting at 1:30 p.m. Eastern Daylight Time (17:30 UT).
Which star will Venus pass closest to?
Venus will temporarily be the brightest star in the Pleiades, but appearances can be deceptive. The star nearest to Venus in the Pleiades (as seen from North America) will be Alcyone, the brightest star in the cluster. However, it’s actually two giant hot “B” stars, with one of them having three smaller stars in orbit. All together, Alcyone is 2,400 times as luminous as our sun. From Europe, Venus will appear to pass closer to Merope.
However, even Alcyone will be far outshone this weekend by a dazzling Venus—shining at magnitude -4.6—against the beautiful backdrop of the Pleiades.
Wishing you clear skies and wide eyes.