The sky, March 25-31: Jupiter, Mercury and on March 30, Comet Pons-Brooks

Special to, March 25, 2024

Excerpts from weekly Sky&Telescope report.


■ If you haven’t spotted Mercury yet this season, look for it lower right of Jupiter as twilight fades as shown below. Jupiter is magnitude –2.1. Mercury this evening is magnitude –0.1, meaning one sixth as bright. And that’s not counting the extra atmospheric extinction that affects low objects.

Jupiter and Mercury in the western twilight, March 24, 2024

Jupiter and Mercury in the western twilight are 23° apart, about two fists at arm’s length. They’ll remain at nearly this separation for the rest of the week.

■ Full Moon tonight (exactly full at 3:oo a.m. EDT Monday morning the 25th). The Moon rises due east around sunset. By 9 p.m. or so, once the Moon is shining high in the southeast, look below or lower left of it by two fists at arm’s length for Spica.

■ This full Moon comes with a deep penumbral eclipse late tonight! You’re in luck if you’re anywhere in the Americas including Hawaii. “Penumbral” means the Moon passes only through the pale outer fringe of Earth’s shadow, the penumbra. Mid-eclipse occurs tonight at 7:13 UT, which is 3:13 a.m. EDT, 2:13 a.m. CDT, 1:13 a.m. MDT, 12:13 a.m. PDT, and 10:13 p.m. Hawaii Standard Time. At that time the Moon’s northeast edge will just miss the edge of the shadow’s dark umbra. That means this just misses becoming a partial lunar eclipse.


■ The huge, bright Winter Hexagon is still in view early after dark, filling the sky to the southwest and west. It’s the biggest well-known asterism in the sky.

Start with brilliant Sirius in the southwest, the Hexagon’s lower left corner. High above Sirius is Procyon. From there look higher upper right for Pollux and Castor (lined up nearly horizontal), lower right from Castor to Menkalinan and then bright Capella, lower left from there to Aldebaran, lower left to Rigel at the bottom of Orion, and back to Sirius.


■ Late this evening the Moon, two days day past full, shines about 4° lower left of 1st-magnitude Spica. Cover the Moon with your fingertip to hide its bright glare.


■ Castor and Pollux shine together nearly overhead in the south after dark. Pollux is slightly the brighter of these “twins.”


■ A serious pre-sunrise challenge: On Friday morning the 29th, use large, well braced binoculars to look for Venus just above your east horizon about 20 or 15 minutes before sunrise. Look about a fist and a half to the right of where the Sun is about to come up.

Got Venus? Now the hard part. This morning, Saturn and Mars form an equal-spaced diagonal line with Venus, extending to its upper right in that order. The three planets are each 8½° apart. But both Mars and Saturn are about magnitude +1.2, only 1/100 as bright as Venus (before atmospheric extinction). Good luck. You’ll need super-clear air.


■ Can you still see Mercury about two fists lower right of Jupiter in twilight? It’s fading fast!

Jupiter and fading Mercury at dusk, end of March 2024

■ Perseus, with Algol on his stick-figure leg, is getting lower in the northwest as the season advances. So, this evening is one of your last good chances until next fall to catch Algol in eclipse. It should be at its minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 6:52 p.m. EDT; 9:52 p.m. PDT. Algol will take several additional hours to rebrighten.


■ Comet Pons-Brooks is low in the west right after dark. At a predicted 5th magnitude it should be fairly easy in binoculars and very interesting in a telescope. Look right after twilight ends. This evening it’s passing only about ½° from 2nd-magnitude Alpha Arietis (Hamal). Look just to the star’s right or lower right. The tail points up.


■ Right after dark, Sirius shines brilliantly in the south-southwest. Lower left of it, by about one fist, is the triangle of Adhara, Wezen, and Aludra, from right to left. They form Canis Major’s hind foot, rear end, and tail, respectively.

Just left or upper left of the triangle, forming a 3rd- and 4th-magnitude arc that’s a bit larger than the triangle, are the three uppermost stars of the constellation Puppis. No it’s not a puppy, despite following right behind the Big Dog. It’s the Poop Deck (stern) of the giant ancient constellation Argo Navis, the ship of Jason and the Argonauts. These three are the only stars of Argo that are readily visible naked-eye from mid-northern latitudes.

Just 1.5° upper right of the middle of the three, binoculars on a dark night will show the little 6th-magnitude open cluster M93. It’s elongated northeast-southwest.

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