There’s nearly always a handful of dim and forgettable comets trudging across the heavens, attracting a few solar system astronomers and keen amateurs with large telescopes. But sometimes one of these faint objects will unexpectedly flare up like a flash bulb and gain wider attention. That’s what’s happened to the obscure Comet 168P/Hergenrother. It brightened last week by a factor of 100 and now lies within easy reach of a small telescope.
While it’s still not a bright object, Comet 168P/Hergenrother flared up just as it reached perihelion on October 1. Astronomers expected the comet peak at a very faint magnitude 15, well beyond the reach of visual observers with small telescopes. But shortly after perihelion, the comet unexpectedly brightened 100x to about magnitude 10.
What caused this sudden brightening? As the Sun baked the surface of the comet, a pocket of ice likely melted and popped open, spewing forth a large amount of gas and dust which reflected more light from the Sun. It was an unexpected event. But that’s the thing with comets… they are unpredictable. Or in the words of my old colleague, the famous comet hunter David Levy, ”Comets are like cats: they have tails, and they do precisely what they want.”
Over this past weekend, Comet Hergenrother spanned about 3-4′ and looked like a fuzzy and elongated star in a 4″ or larger telescope. And it’s bright enough to see in 50 mm or larger binoculars in very dark sky, though it will be hard to distinguish from the surrounding stars.
If you’re ill equipped to spot the comet for yourself, here’s an image taken last night by Bob and Debbie Fitzhenry at Cosmic Obsession…
This week, the comet is about 135 million miles from the Sun and just half as far from the Earth. It’s passing through the northeast section of the Great Square in Pegasus over the next week (see map below)…
Comet 168P/Hergenrother was discovered in 1998 by Carl Hergenrother. Astronomers first thought it had an open parabolic orbit, which meant it would visit the Sun only once before being hurled for good into the far reaches of the solar system. But the comet returned in 2005, and astronomers now classify it as a periodic comet which returns every 6.9 years.