Astro Bob: Venus-Jupiter convergence, Comet ZTF meets Mars, Aldebaran

Jupiter Venus approach — On Feb. 5, Jupiter and Venus stood about 25° apart in the southwestern sky. On Thursday night, Feb. 9, they'll be 5° closer, and their separation will continue to shrink.

By Bob King

February 09, 2023 at 6:20 PM

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?

Venus orbit view — From our perspective Venus slowly moves up and away from the sun (toward the east) in the coming weeks and months. As it does it approaches Jupiter, which is sliding westward. The two meet meet on March 1. As the angle Venus makes with the sun and Earth changes so does its phase. Through a small telescope the planet looks like a tiny gibbous moon at the moment, but it will gradually wane to half by June 4. (Not to scale)

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.

Seasonal star drift Earth orbit V2 S.jpg — As the Earth revolves around the sun we face a different in space at different times of year. For example, in December and January, we look toward Orion at nightfall, but in May and June, Scorpius dominates. Likewise in summer we face toward the center of the Milky Way galaxy, while in winter the center is to our backs. The Earth's orbital motion causes the stars in the eastern sky to rise four minutes earlier each night and those in the west to set four minutes earlier. Over days and weeks, the minutes accumulate, and the stars slowly drift westward.

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's moons — All four of Jupiter's brightest moons — Callisto (C), Europa (E), Io (I) and Ganymede (G) — line up with the planet on Feb. 12. This is the small telescope view. They'll scrunch closer together in binoculars and look like tiny stars in Jupiter's glare.

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.

Comet ZTF Feb map 1 — On Feb. 10 and 11, Comet ZTF appears close to the planet Mars, an ideal opportunity to spot it in binoculars. Mars is the bright, reddish "star" to the left of the Pleiades and directly above a similarly-colored but somewhat fainter star, Aldebaran.

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.

Comet ZTF map Feb 12-16 — Use this map from Feb. 12-16 as the comet dips below Mars and passes Aldebaran. To find Aldebaran you can either use Mars or just shoot a line upward through Orion's Belt, and it will take you straight there.

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.

Astro Bob: Venus-Jupiter convergence, Comet ZTF meets Mars, Aldebaran

The mid-February night sky is busy with celestial get-togethers.