Comets are among the most beautiful sights in the night sky.
For a few weeks maybe, they grace the sky before vanishing again. We see a glowing head followed by a misty, veil-like, streaming tail, millions of kilometres long. They have elliptical orbits taking them between the cold, dark, outer reaches of the Solar System, where they spend most of their time, and the inner regions, closer to the Sun, where we live.
While far from the Sun, the comets are lumps of dirty ice a few kilometres in diameter. When they move closer to the Sun, their material starts to evaporate. The icy glue holding the dust particles disappears, leaving the material to float off into space, forming the tail.
Today, most new comets are discovered by special survey telescopes intended to spot Earth-threatening asteroids. Before these instruments, comets were discovered by observers, often amateurs, carefully searching the sky.
There are still amateur comet searchers today, but they have to be lucky to beat those survey instruments. The objective is to discover new comets, or returning known ones, while they are still far out in space, and only beginning to develop the tails that will make them so spectacular when they get closer to the Sun.
What the observers are patiently searching for is a somewhat fuzzy-looking, very faint, possibly star-like object that changes position against the background stars night to night. The procedure is to spot a "fuzzy", make a careful note of the time, date and where it is against the background stars, and then go back a day to a few days later, find it again and carefully note its position.
If it has moved it could be a comet. However, there are other faint “fuzzies” out there.
We have all seen the beautiful pictures of distant galaxies and the gas and dust clouds in our galaxy obtained using large telescopes such as the Canada France Hawaii Telescope, or space-borne telescopes like the Hubble Space Telescope and the James Webb Space Telescope.
They are beautifully coloured by reflected starlight and the pink glow given off by hydrogen when illuminated by ultra-violet light from young stars. It is therefore a bit of a disappointment when these objects are seen directly through a backyard telescope, even a large one. Instead of the colours there are faint wisps, with elusive detail and hints of colour creeping into view as our eyes get fully adapted to the low light levels.
The wonderful pictures we see in publications require collecting those elusive light photons for minutes or hours. Our eyes use only very short exposures. Having skies full of faint “fuzzies” that are not comets means comet hunters need to recognize those false alarms. Waiting many days in order to be absolutely sure that “fuzzy” has moved could mean the credit for the discovery could go to someone else. At least nowadays there are catalogues of nebulae and galaxies, making it easier to identify those false alarms.
This was not the case back in the late 18th Century, when French astronomer Charles Messier was comet hunting. He had to laboriously check out every faint “fuzzy” he saw, to see if it could be a comet, as opposed to being a distant dust or gas cloud, galaxy or a star cluster.
After having been deceived more than once, he decided to catalogue all those fuzzy objects to be avoided: all those non-comets. As he continued his searching, he gradually accumulated a catalogue of 110 objects, recording their position and appearance.
The object numbered Messier 1 (or just M1) in the catalogue is the Crab Nebula, a cloud of glowing gas surrounding an exploded star. M31 is the great galaxy in Andromeda. It is a bit ironic that today Charles Messier, the comet hunter, is best known not for his searches for comets, but for his catalogue of faint, fuzzy objects to be avoided.
• After sunset, Saturn lies low in the southwest, Jupiter higher in the south and Mars even higher in the southeast.
• The Moon will be full on Jan. 6.
This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.