The latest Comet Lovejoy is 5th magnitude in late December and should reach 4th magnitude in January, when it will be nicely placed high in the dark for your binoculars or telescope. It's visible to the unaided eye under good sky conditions.

Update Dec. 30: As Comet Lovejoy enters its best time of viewing, see our newest post for updated information on the comet's progress.

Update Dec. 28: The comet has reached magnitude 5.0! It's in Lepus, easily visible now from northern latitudes in late evening when Orion stands high. Tonight (Sunday) it passes by the globular cluster M79, which is smaller and much fainter at magnitude 8.4. From Sky & Telescope's hometown at latitude 42° north, the comet is a big puffball in 10×50 binoculars even through suburban light pollution. It appears moderately concentrated toward the center, with a hint of being asymmetric but no visible tail. But the tail is there alright, as numerous amateur photos are showing.

Update Dec. 15: Comet Lovejoy is brightening faster than expected. Last night it was visual magnitude 6.1, estimated by veteran comet observer Alan Hale using 10×50 binoculars with the comet very low in his sky. From Australia, where the comet currently passes overhead, David Seargent says that on December 13th he "just managed to glimpse 2014 Q2 naked eye in a very clear sky. I estimated it at mag. 6.1 and at 6.2 with 2×25 opera glasses." Then on the 14th: "Much easier to see naked eye than 24 hours earlier, and estimated as bright as 5.5!" That same night Michael Mattiazzo in Australia estimated it at 6.0, and Paul Camilleri reported 5.7. At this rate Comet Lovejoy would crest at about 4.1 in mid-January.

A new Comet Lovejoy, designated C/2014 Q2, is heading our way out of deep space and out of the deep southern sky. It may brighten to 5th magnitude from late December through much of January as it climbs into excellent viewing position for the Northern Hemisphere, high in the dark winter night.

This is Australian amateur Terry Lovejoy's fifth comet discovery. He turned it up at 15th magnitude in Puppis last August, in search images that he took with a wide-field 8-inch scope. It hasn't moved very much since then — it's still in Puppis as of December 11th — but it's hundreds of times brighter now at visual magnitude 6.8, reports David Seargent in Australia. On December 9th "I saw it easily using a pair of 6x35 binoculars," Seargent writes. Using a 4-inch binocular telescope at 25×, he says it was a good 8 arcminutes wide with a strong central condensation and no visible tail.

And it's picking up speed across the sky for a long northward dash.

A Comet of the High Dark

"Comet Q2," as some are calling it, will skim through Columba south of Orion and Lepus from the nights of December 16th through the 26th, brightening all the while, as shown on the finder charts for December and January below and on the print-friendly versions here: December, January. The dates on the charts are in Universal Time, and the ticks are for 0:00 UT.

The comet spends the last few days of December in Lepus at perhaps 6th magnitude, though by then the light of the waxing Moon (at first quarter on the 28th) will start to be an annoyance. On New Year's Eve, a little after January 1st Universal Time, look for the comet just off Lepus's forehead as shown on the charts.

The Moon brightens to become full on January 4th. Most of us won't get a dark moonless view again until early in the evening of January 7th, with the comet now crossing northernmost Eridanus. That's the same day it passes closest by Earth: at a distance of 0.47 a.u (44 million miles; 70 million km). That's also about when it should start glowing brightest for its best two weeks, as it crosses Taurus and Aries high in early evening.

By then the comet is starting to recede into the distance, but its intrinsic brightness should still be increasing a bit; it doesn't reach perihelion until January 30th, at a rather distant 1.29 a.u. from the Sun. By that date the comet should be starting to fade slightly from Earth's point of view. In February it will continue north between Andromeda and Perseus as it fades further, on its way to passing very close to Polaris late next May when it should again be very faint.

Originally Comet Q2 wasn't expected to become this bright. We're basing these predictions on an analysis by J. P. Navarro Pina in late November using the comet's visual behavior for the previous several weeks. Whether it will continue to brighten on schedule is anybody's guess, but the odds are good; comets that don't come near the Sun are more predictable in their brightnesses than those that do.

Q2 is a very long-period comet, but this is not its first time coming through the inner solar system. On the way in, its path showed an orbital period of roughly 11,500 years. Slight perturbations by the planets during this apparition will alter the orbit a bit, so that it will next return in about 8,000 years.

Oh, and that lovely green color? Comet heads are usually like that. The green glow comes from molecules of diatomic carbon (C 2 ) fluorescing in ultraviolet sunlight in the near-vacuum of space. (In addition cyanogen, CN, can add some violet to the green, but our eyes are fairly insensitive to violet.) Here's a spectrum of a comet's head with the emission lines labeled.

By contrast, a comet's ion tail (gas tail) — the narrow, often detail-filled part of the tail that points directly away from the Sun — is tinted blue. The ion tail's color comes from fluorescing carbon monoxide ions (CO+).

Dust in a comet's head and tail simply reflects sunlight, so it appears Sun-colored: pale yellowish white. The greatest comets tend to get that way by being very dusty, so the most memorable naked-eye comets are usually remembered as white. Examples were the spectacular Comet Hale-Bopp of 1997 and the grand sungrazing Comet Lovejoy of 2011, C/2011 W3. But the current Comet Lovejoy is producing very little dust.

For more to see with your binoculars, check out Gary Seronik's Binocular Highlights.