Astro Bob: Venus-Jupiter convergence, Comet ZTF meets Mars, Aldebaran
The mid-February night sky is busy with celestial get-togethers.
While I get jazzed hunting faint supernovas and comets I also love the easy, bright stuff. It's a joy to just look up and see what's happening without special equipment. For the next few weeks we can watch a wonderful, slow dance of the two brightest planets, Venus and Jupiter. To find them, face southwest about an hour to 90 minutes after sunset and look up. Both look like brilliant stars.
Venus is the lower of the two, located about 20° or two balled fists held at arm's length from Jupiter. If you reach your fist to the sky and measure the distance between them on successive nights, you'll soon see that they're drawing closer together to the tune of about one degree per night. That's equal to the width of your pinkie held against the sky. In just a few weeks — on March 1 — they'll appear to nearly "collide" in a spectacular conjunction. What makes planets come together like this?
Two things are happening. First, Venus is moving up and away from the western horizon. In the diagram you can see that the planet is still relatively near the sun in February from our earthly perspective. But in the days and weeks ahead, it climbs higher and higher, gradually approaching Jupiter. Months from now on June 4, Venus will reach its greatest apparent distance from the sun and then slowly slide back toward it.
Meanwhile, Jupiter is sinking in the west along with the rest of the stars in that half of the sky. Every night, stars in the eastern sky rise 4 minutes earlier while those in the west set 4 minutes sooner. This slow, celestial drift from east to west is caused by Earth's revolution around the sun. As the planet moves along its orbit, we approach stars in the eastern direction and leave behind those in the west. Paired with the ascent of Venus, the two planets will meet soon enough!
Jupiter is not only a brilliant, naked-eye sight but worth a peek in binoculars, too. Anywhere from one to four of its brightest moons are visible in 35mm and 50mm binoculars depending on how close the moons are to the planet at the time. On Feb. 12, all four of them — Io, Europa, Ganymede and Callisto — are neatly aligned far enough on either side of Jupiter to potentially see them all in steadily-held binoculars.
Comet ZTF (C/2022 E3), a.k.a. the green comet, is still flying around up there and visible in binoculars for the next week or so. Lucky for us, it continues to pass near bright, easily-recognizable stars. On Friday and Saturday nights (Feb. 10-11) it will pass within 1.5° of the golden-red planet Mars. Just find Mars, focus sharply and you'll see a fuzzy glow to its upper left (Feb. 10) and then again to its lower left the following night. Comet and planet are close enough to easily fit in the same field of view.
Then around Valentine's Day (Feb. 14), the comet will appear just to the left of reddish-orange Aldebaran, the brightest star in Taurus the bull. It's fading now but should still be visible from reasonably dark skies in binoculars and small telescopes. Under a very dark sky on Feb. 8 it was barely visible with the naked eye but super easy in 10x50 binoculars.
Like a friend we haven't seen for years, we delight when a comet comes to visit but also feel a twinge of sadness at its departure.