On a clear dark night, Comet Lovejoy is just about bright enough to be glimpsed as a small smudge of light with the naked eye.
Through a small telescope or binoculars it appears as a softly glowing, bluish green ball.
Like other comets, Lovejoy is a big chunk of ice and dust orbiting the sun. It belongs to the family of “long period” comets, which means it takes a long time to travel in from the fringes of the solar system.
The object last passed through the inner solar system 11,500 years ago, and is not expected to return for another 8,000.
Yesterday, the comet reached its closest point to the Earth, a distance of 70m kilometres, but it will remain easy to spot for about the next two weeks.
Robin Scagell, vice-president of the Society for Popular Astronomy, said: “I was looking at it a couple of nights ago. It’s a circular fuzzy ball that is easy to see with a pair of binoculars.
“It appears bluish green and is quite pretty, but not dramatic. I would call it a good workmanlike comet.
“The nice thing about it is that its visible at night rather than at dawn or dusk.
“A lot of people have been out photographing it. Its possible to get a decent picture with a fairly short exposure time just using a good camera with a telephoto lens.”
The comet was discovered on August 17 last year by Australian amateur astronomer Terry Lovejoy, who spotted it in images taken by his 20cm backyard telescope.
Currently it can be found by looking to the right of Orion, about two hand widths below the “seven sisters” Pleiades star cluster.
Anyone hoping to catch Comet Lovejoy will be well advised to watch the weather forecasts as well as the sky.
The comet’s icy nucleus is at least 3km or 4km across. But the object’s visible head, or coma, is a much larger cloud of gas and dust roughly 640,000km wide.
Its green hue is produced by molecules of diatomic carbon in the coma that fluoresce under the Sun’s ultraviolet rays. In contrast, the comet’s delicate gas tail is tinted blue thanks to fluorescing charged molecules of carbon monoxide.
Unlike some of the most spectacular comets, Lovejoy does not possess a dramatic dust tail containing millions of particles that reflect sunlight. Over the next two weeks, the comet crosses the constellations of Taurus, Aries and Triangulum, climbing higher in the sky.