Comet Catalina, currently the brightest comet in the sky, will be gliding across the Big Dipper this week and next as it heads toward its closest approach to Earth on January 17th at a distance of 67.4 million miles (108.4 million km). It’s about magnitude 6.5 or a bit below the naked eye limit, but visible as a small, round puff of light in a pair of 40mm or larger binoculars (8×40, 7×50, 10×50) or small telescope. If you look closely you’ll notice the comet is brighter in the center where its atmosphere is thickest.
I’m excited to see Catalina enter the evening sky: we don’t have to get up before dawn for a view, the bright Dipper stars make it easy for almost anyone to find it, and the comet’s ripping along at some 2° per day, giving us a sense of its tremendous velocity through space. If you haven’t seen it yet, now’s the time. Ever since emerging into the morning sky in December after making its closest approach to the sun, Catalina’s been a striking object in deep astrophotos with two bright tails, a broad tail of dust particles boiled off the comet’s icy surface, and a pale blue ion tail composed of fluorescing gas.
You can still see both in recent images but they tend to blend together when viewed through the telescope into one fat swath of hazy light. Because Comet Catalina will be moving rapidly northward, telescope users will notice its movement across the background stars in 15-30 minutes.
On Thursday the 14th, watch for it to pass a little more than 1 (two full moons) from Alkaid at the end of the Dipper’s Handle. Center your binoculars on Alkaid and bingo, the comet will be right there. The comet also passes by another fuzzy object, the galaxy M101, better known as the Pinwheel. When you see them together, consider that the Pinwheel is 170,000 light years across or 70% larger than our Milky Way galaxy and about 23 million light years away. Both comet and galaxy will appear as similar smudges of light.
Catalina originally resided in the Oort Cloud, a rich reservoir of comets located at the fringe of the solar system. Something, perhaps a star that passed relatively nearby, gave it a slight kick, altering its orbit and sending it toward the sun and grateful skywatchers on planet Earth. Its inbound journey took an achingly long several million years. During its solar swing-by, the comet picked up enough speed to eventually blast right past the Oort Cloud into interstellar space. Gone. Adios! That makes this our first and last time we’ll ever see this fuzzy emerald gem. Don’t miss it.