WASHINGTON, January 10, 2015 — Sky-gazers will be able to see the green-glowing comet Lovejoy with only binoculars – or possibly even the naked eye in the right conditions – for the next two weeks. Lovejoy, officially cataloged as C/2014Q2, will be at its brightest and shiniest between now and January 24.
The comet was at its closes point to the earth on January 7, a mere 44 million miles, and will get only slightly farther away over the next few weeks. Although it is now moving away from the earth, its intrinsic brightness will actually increase slightly until January 30, when it is closest to the sun.
Comet Lovejoy will not come this close to Earth for another 8,000 years.
After January 30, the comet will be more difficult to see, and astronomers will be further hampered by the return of the moon in late January. The comet will travel north in February and fade from earth-viewers sight as it passes between Andromeda and Perseus.
Astronomers say the comet will glow at fourth magnitude for the next several weeks. Hipparcus and Ptolemy first invented the star magnitude measurement by dividing stars into six magnitudes. A sixth magnitude star is barely visible to the naked eye in favorable conditions. Toward the end of the 2-week window, the moon will be waning, with virtually no moon light to distract from the comet from January 18 to January 23.
By May, the comet will pass close to Polaris and will likely register only a 12th magnitude.
Amateur Australian astronomer Terry Lovejoy discovered the comet – then at 15th magnitude – in August 2014 from his rooftop observatory. The comet was then located in the southern constellation of Puppis the Stern and was moving northward. Lovejoy has discovered four other comets, including C/2011 W3 and C/2013 R1. Immediately after Comet Lovejoy was discovered, astronomers estimated that it would not get brighter than eight magnitude.
The green color of the comet is consistent with usual behavior of comet heads. Comet heads glow green because of molecules of diatomic carbon fluorescing in ultraviolet sunlight. The comet also contains cyanogen, a poisonous gas, that creates violet colors. However, human eyes have difficulty seeing those shades. Comet tails usually have a blue tint, from molecules of carbon monoxide ions fluorescing in ultraviolet sunlight.
Comets also produce dust, which reflects sunlight and appears white or pale yellow. Comets which produce high amounts of dust, like the 1997 Hale-Bopp Comet, are very bright and often appear white to the naked eye. This year’s Comet Lovejoy is producing very little dust, so it continues to appear green rather than white.
To see Comet Lovejoy, find an area with little light pollution. The comet will be high in the early evening sky. The best reference point to see Comet Lovejoy is the constellation Orion. Lovejoy advised comet-watchers to “Look up to his left knee and then drift across toward the left and scan that area.”