Time to check in on our current favorite comet. It was discovered by American astronomer Carl Wirtanen in January 1948. The “46P” part refers to it being the 46th periodic (P) comet discovered. Periodic comets, also known as short-period comets, revolve around the sun in fewer than 200 years. Those that take longer are called long-period comets. Wirtanen completes an orbit every 5.4 years.
Under clear, dark skies last night (Dec. 7) I could see the comet without any optical aid because I knew exactly where to look. Even then it was little more than a faint smudge glowing at magnitude 5. But hey, it’s official — we have a naked-eye comet! Binoculars gave a great view of a moon-sized fuzzy blob of fuzz with a brighter center. In a 15-inch telescope Wirtanen was a big, gassy-looking thing with a pale blue color and small, brighter core called the nuclear region. The nuclear area is the bright central pip that really pops in recent photos of the comet. It’s much more obvious in images than seeing it visually in binoculars.
I also teased out slightly brighter streak of light embedded in the coma’s head pointing to the northeast. This is the gas tail. Because of 46P’s near head-on approach to Earth, we won’t see an obvious tail for some time. The gas tail shows up clearly as a narrow streak in time-exposure photos. Over the coming week, the comet is expected to brighten further to magnitude 3, so it should become more obvious from dark skies. I’ve heard that city observers are having a tough go of seeing it in light pollution. That’s not surprising given how soft and fuzzy it appears.
I’ve included the map again to help you make the best of the current run of moon-free skies to see 46P/Wirtanen at its best. When you’re using binoculars, point them at the comet’s position and look for a soft, misty glow like a little puff of cloud. As Wirtanen approaches the Earth, it picks up speed, moving several degrees northward and higher in the sky each night. That and its expected brightening as it passes closest to us on the 16th should make it easier to see in the coming week. To make sure you don’t miss it, go for a drive in the country. You’ll also be treated to great views of the winter Milky Way, now rising in the eastern sky in Gemini and Orion like chimney smoke on a still night. Don’t forget those binoculars!