Comet Lovejoy was accidentally imaged by a 570 megapixel camera designed to record dark energy. The composite photo, never meant to be recorded, may be the best image yet taken of the comet.
The Cerro Tololo Inter-American Observatory in Chile utilizes an automated targeting system that records images over large fields. The camera used is the most powerful digital camera on the planet.
The accidental photograph was recorded on December 27, 2014, while the comet was present in southern skies. At the time the image was taken, the icy body was 51 million miles from Earth.
"This was an accidental catch, because Dark Energy Camera scans the sky methodically over a very large region of the sky. Comet Lovejoy only takes up a very small part of the sky, and we didn't intend to point at it, but the camera happened to scanning that part of the sky at that time," Brian Nord of the Cerro Tololo Inter-American Observatory said.
The nucleus of Comet Lovejoy is around three miles in diameter, and the shroud of dust and gas surrounding the object is about 400,000 miles from side to side.
Dark energy is one of the most bizarre components of the universe. As the universe expands, the rate at which galaxies are separating is increasing. This is just the opposite of what would normally be expected - fragments of a firecracker, for instance, slow down after an initial acceleration. Dark energy was originally proposed to explain how the expansion of the universe could be accelerating.
The Dark Energy Camera is able to record images from objects up to eight billion light years away from Earth. However, the observatory occasionally records bodies far closer to our home planet.
"It reminds us that before we can look out beyond our galaxy to the far reaches of the universe, we need to watch out for celestial objects that are much closer to home!" the Dark Energy team reported.
Comets are often described as "dirty snowballs." The objects are composed of dry ice and frozen water, together with small pebbles of rocks, dust, and chemicals such as ammonia. Many form far from the Sun, and are nudged toward the inner solar system. As they approach our parent star, the heat causes gases to rise from the icy body, and solar wind pushes the material away from the sun, forming the distinctive tail of comets.
Comet Lovejoy was discovered by Australian amateur astronomer Terry Lovejoy on August 17, 2014. The distinct green color is caused by cyanogen and diatomic carbon (molecules of pairs of carbon atoms) fluorescing from ultraviolet light generated by the Sun. Carbon monoxide in the tail produces a blue glow seen in many photographs.