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Comet 220P McNaught puts on an encore performance
edited by Lisa Lock , reviewed by Andrew Zinin
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Add as preferred source It has been a busy month for astronomy. In the midst of an eclipse season bookended by the total solar eclipse on Aug. 12 and the deep partial lunar eclipse coming up this week on Aug. 28, an outbound comet hanging high in the dawn sky just refuses to die: 220P/McNaught.
We wrote about this active comet earlier this year, leading up to its favorable 2026 perihelion apparition.
Periodic comet 220P was first discovered by prolific comet hunter Robert McNaught on the night of May 20, 2004, as he was observing from the Siding Spring Observatory in Australia. On a 5.5-year orbit , the periodic comet is a Jupiter-family member, caught long ago in the inner solar system on a 2:1 resonance with the gas giant.
The comet reached perihelion earlier this summer on June 14, 1.6 Astronomical Units (AU) from the sun, just outside the orbit of Mars. Comet 220P is due to make its closest pass to Earth on Oct. 12, at a distance of 1.043 AU. The comet is running ahead of us on its outbound orbit, loitering for most of the summer in the dawn sky.
What's really grabbed astronomers' attention are the recent outbursts from this normally obscure comet. A large eruption in early June vaulted the comet nearly 10 magnitudes in brightness, an 8,000-fold increase surpassed only by 17/P Holmes in 2007 and Comet 289P/Blanpain in 2013. Early August saw another marked increase of 600 times, or about 7 magnitudes. Something interesting is afoot with Comet 220P, and I would not be surprised if we saw another outburst leading up to its closest Earth passage in October.
The comet topped out at more than magnitude +8 in June and is still holding steady at a respectable magnitude +9 in late August. The comet joins the ranks of another notable active comet we've been following in 2026, Comet 10P Tempel .
Astrophotographer Dan Bartlett is composing a sequence of images showing the comet's progress through the summer.
There's a true "multi-personality of this comet, (it) almost looks like a different comet," from one night to the next, Bartlett notes on his AstroBin page . "The blue-green coma expands at first and then dissipates and contracts as the nights progress. A faint dust tail can be seen in the early days of the outburst and all but disappears after Aug. 10." The sequence then shows the tail starting to unfurl again this past week.
Comet 220P spends the end of August 2026 between the stars Omicron Tauri and Lambda Ceti. The comet then loops in and out of the Circlet of Pisces asterism through the remainder of 2026, circling the magnitude +2.5 star Alpha Ceti (Menkar). This puts Comet 220P high to the south for Northern Hemisphere observers in the predawn hours through August, September and October.
I usually consider a comet to be of interest to visual observers and backyard imagers when it breaks magnitude +10, and of public interest when it tops magnitude +6 or brighter. Keep in mind, unlike a pinpoint star, the brightness of a comet like 220P is spread out, much like a deep-sky object such as a globular cluster.
These sorts of binocular comets, however, are great targets for smartscopes like the SeeStar or Dwarf Lab's Dwarf Mini .
Comet 220P McNaught reaches aphelion 4.679 AU from the sun on March 12, 2029, and we'll see it again on its next perihelion apparition in late 2031.
Could we witness a breakup before Comet 220P McNaught departs the dawn sky scene in late 2026? One thing is for certain: In an otherwise clockwork universe, comets seem to have a "mind of their own" when it comes to outbursts and changes in brightness. Be sure to keep an eye on 220P McNaught into fall, as its final act for 2026 may be yet to come.
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