Comet 41P/Tuttle-Giacobini-Kresak should become bright enough this coming week to see in 10×50 binoculars as it hurries across Ursa Major the Great Bear. 41P returns to Earth’s vicinity every 5.4 years. Some years it plays out that the comet is particularly close to Earth. 2017 is one of them. On March 31-April 1, the comet will pass just 13.2 million miles away or 55 times the Earth-moon distance — its closest in more than a century.
That’s great news for skywatchers, since it means that 41P/T-G-K could briefly become bright enough to see with the naked eye from a dark, rural sky around that time. Right now, it’s about magnitude +8 and appears as a faint, misty patch of light in binoculars. Photographs show that the comet has a very large coma nearly 1° across or twice the size of the full moon according to some estimates.
Best of all, at least if you live in the northern hemisphere, is that 41P is “circumpolar.” That means it’s in the northern sky and close enough to the polestar, Polaris, to never set. As the comet speeds across the bowl of the Big Dipper this week and into Draco the Dragon, it will remain visible all night and well placed for viewing in moonless skies through early April. You’ll have lots of chances to see it assuming that clouds don’t park themselves over your rooftop.
In a telescope, the comet will appear large, fuzzy and very diffuse with a brighter center. Using high magnifications of 200x and up, observers should watch for jets of material extending from the inner bright, “false” nucleus. The true nucleus, a solid body composed of dusty ice, is about 0.8 mile across (1.4 km) across and completely hidden by the dust that gets boiled off when sunlight vaporizes comet ices.
41P, while not bright like Comet Hale-Bopp or some other notables, takes center stage as the current brightest. Grab a pair of binoculars and watch its progress across the Dipper the next clear night.