Astro Bob: Gossamer moon joins Mercury on May 2

The two-day-old crescent lines up with Mercury and the Pleiades Monday night. A bright comet was supposed to join the scene, but it recently disintegrated.

Mercury and moon
Watch for the 2-day-old moon, Mercury and the Pleiades at dusk Monday, May 2. They're best visible low in the western sky about hour (or a little more) after sunset. The trio form a line about 7 degrees long. The potential, binocular-bright Comet PanSTARRS (C/2021 O3) unfortunately crumbled after its close passage of the sun in April.
Contributed / Stellarium

If you haven't seen Mercury yet, it's fading. Why not take advantage of Monday night's moon for a helping hand? The two-day-old crescent will stand about 4.5 degrees above and left of the elusive planet. Point your binoculars at the moon (a gorgeous sight in itself), focus sharply, then slide about one binocular field of view to the lower right. You should see a single bright star โ€” that's what you're after!

In early May, the planet shines about magnitude 0.8. Although it's growing in size as it gets closer to the Earth, Mercury's also getting fainter because its phase has waned from full to crescent. Through a small telescope it will appear 27% illuminated Monday night. The moon is much thinner โ€” only about 5% lit. Further down in the sky below Mercury you'll find the Pleiades. All three look best in binoculars.

Panstarrs O3 Jan 6 2022 Michael Jaeger.jpg
Comet PanSTARRS (C/2021 O3) โ€” at center โ€” was very faint but still in one piece with a short tail back on Jan. 6, 2022. It was discovered July 26, 2021, using the Panoramic Survey Telescope And Rapid Response System (PanSTARRS) telescope atop Mt. Haleakala in Hawaii. After passing closest to the sun April 21, it started to break up and fall apart.
Contributed / Michael Jaeger

I wanted to bring you good news about Comet PanSTARRS. Had it survived its close brush with the sun April 21 at a distance of 26.7 million miles (43 million kilometers), it might have been bright enough to see in binoculars at around magnitude 5.

Instead, it appears to have lost its head. Astronomers have detected only a faint, glowing cloud of debris โ€” a sure sign that it has begun to disintegrate. Gravitational tides from the sun, coupled with intense heating, were too much for the friable object. Comet experts weren't particularly surprised because PanSTARRS was small to begin with. Still, it's disappointing news.

You win some, you lose some. As Comet PanSTARRS arcs farther from the sun in the coming nights, I'll try to spot it anyway. Even crumbling comets are fascinating to watch. Everything is a process, and the more steps of the process we see, however faint or obscure, the better our understanding of the natural phenomenon.


"Astro" Bob King is a freelance writer for the Duluth News Tribune.

"Astro" Bob King is a freelance writer and retired photographer for the Duluth News Tribune. You can reach him at
What To Read Next
Get Local