Many of us look forward to bright comets. They’re among the most beautiful objects to see in the night sky. The last truly memorable one for Northern Hemisphere skywatchers was Hale-Bopp in 1996 and 1997. All you had to do was open the front door and face the northwestern sky — it hung like a painting there for weeks. For the Southern Hemisphere it was the Great Comet of 2007, better known as Comet McNaught. But even a modest naked-eye or binocular comet is something of a rarity, the last being Comet Wirtanen which brightened to 4th magnitude in late 2018.
This spring there are four comets (and soon a fifth) bright enough to spot in a pair of 50mm binoculars from dark skies. One of them, Comet SWAN, is faintly visible without optical aid from the far southern U.S. and Southern Hemisphere. As it moves northward in the sky it’s expected to reach magnitude 3 — one level of brightness fainter than the stars of the Big Dipper — around May 21-25. Keep in mind however that all comets are subject to change and have a way of defying predictions. But assuming it follows the “rules” it should first become visible to most U.S. and Canadian observers around May 18 when it will appear very low in the morning sky below the Square of Pegasus.
Finding it then won’t be particularly easy because the comet will stand only about 5° high around 3:45 to 4 a.m. from the central U.S. That’s equal to the amount of sky covered by three fingers held together at arm’s length. Dawn complicates matters. At the same time the comet the sky will slowly brighten. To make sure you don’t miss it you’ll need to be out at just the right time. For many locations that’s between about 3:30 and 4 a.m. Make sure your observing site has a wide-open vista as far down to the east-northeast horizon as possible.
Binoculars will also be essential. While this fuzzy visitor is officially naked-eye brightness it will appear fainter because it’s low in the sky. When we look along the horizontal we see through the thickest, dustiest part of the atmosphere which absorbs light and makes otherwise bright objects, even the moon, appear fainter compared to when they’re higher up.
I’ll start looking as soon as May 18, but if you’re no friend to waking up at dawn you can wait until May 22 and observe Comet SWAN in the evening. While the comet will continue to “take the low road” across the northern sky we’ll have the opportunity to see it in complete darkness. Again, bring binoculars to best appreciate the fragile, frozen object with its delicate tail pointing nearly straight up. Once you spot in the binoculars, lower the glass and see if it’s also visible with the naked eye.
Yet another bright, low-lying, 3rd magnitude comet will appear in the dawn sky in mid-July called NEOWISE (C/2020 F3). It’s named for NASA’s orbiting Near-Earth Object Wide-field Infrared Survey Explorer telescope (NEOWISE) which discovered the object in late March. It rapidly brightened in April and should put on a nice show right about the time mosquitos are most voracious. Sorry, just an attempt at humor. I’ll have more to say about the NEOWISE comet next month.
Binocular and telescope observers have more than just SWAN to sate their comet cravings. Comet ATLAS (C/2019 Y4) which broke apart last month and began to fade recently experienced an outburst in brightness to about magnitude 8 and may now visible in binoculars under a dark sky. Add in Comet ATLAS (C/2019 Y1) — also around magnitude 8.5 — and Comet PANSTARRS (C/2017 T2) at 8 and wow, that’s a lot of binocular comets! Of course, a telescope will work better on these three but give them a try in your glass.
Of course, I hope you get to see them all including SWAN which will be swimming your way very soon!