Tonight and every night for the next week or so you have the chance of taking part in an extraordinary marathon. No running is involved. All that's needed is a clear night, warm clothing and a telescope.
Serious astronomers call it the Messier Marathon after the 18th-century French astronomer Charles Messier, who first began to catalogue some of the more unusual celestial objects of the night sky. If you can see and count all 110 Messier objects, the marathon is done.
On the night of 23-24 March 1985, Gerry Rattley from Dugas, Arizona, was probably the first person to complete the Messier Marathon in one session - aided by the crystal-clear sky in his part of the world. Some amateurs aim to do it in one night, others are content to take a week.
This time of the year, after the vernal equinox and with the help of a new moon and a cloudless sky, is an especially good time to attempt the Messier Marathon. But it is a formidable task and even seasoned professionals admit that there are still some objects in the catalogue that they have yet to observe.
"It's a very serious challenge," said Professor Mark Bailey, director of the Armagh Observatory. "It's a bit like an amateur runner trying to do the mile in four-and-a-half minutes."
Charles Messier began cataloguing the "Messier" or "M" objects when he first detected a misty cloud of light on the night of 12 September 1758. "This nebula had such a resemblance to a comet in its form and brightness that I endeavoured to find others, so that astronomers would no more confuse these same nebulae with comets just beginning to appear," he later wrote.
The Andromeda galaxy is listed at M31 in the Messier catalogue. The Orion Nebula is M42, and M45 is better known as Pleides, or the "seven sisters", which are easily visible with the unaided eye.
Professor Bailey said that to Messier and his contemporaries, many of these objects did not look like ordinary stars or planets. "At the time people were not clear what these smudgy objects were. After all, people had just got used to the idea of the Earth going around the Sun," he says.
With bigger and better telescopes, astronomers began to distinguish between distant galaxies, true nebulae of gas clouds and remnants of massive supernova explosions, such as the Crab nebula first observed by Chinese astronomers in the 11th century.
Going through the catalogue, even if you don't make it to the end, is like taking a tour through the history and the science of astronomy, says Professor Bailey. "When you do the marathon you are making a contact with the history of astronomy, and you are making contact with the huge diversity of objects in the Universe."
It took a lifetime for Messier to compile his catalogue, which was interrupted at one stage by serious injury after he fell into an ice cellar. Now anyone with a good telescope can follow in his footsteps, with some help from the weather.
For details on how to embark on the Messier Marathon, visit www.universetoday.com
Many of the objects in Messier's Marathon are identified only as numbers. The others are called:
M1 Crab nebula; M6 Butterfly cluster; M7 Ptolemy's cluster; M8 Lagoon nebula; M11 Wild Duck cluster; M13 Great Hercules Globular cluster; M16 cluster associated with the Eagle or Star Queen nebula IC 4703; M17 Omega nebula; M20 Trifid nebula; M24 Milky Way Patch; M27 Dumbbell nebula; M31 Andromeda galaxy; M32 satellite galaxy of the Andromeda galaxy; M33 Triangulum galaxy; M40 Double Star, Winnecke 4; M42 Orion nebula; M43 de Mairan's nebula; M44 Praesepe, the Beehive cluster; M45 Subaru, the Pleiades; M51 Whirlpool galaxy; M57 Ring nebula; M63 Sunflower galaxy; M64 Black Eye galaxy; M73 System or Asterism of Four Stars; M76 Little Dumbbell, Cork, or Butterfly nebula; M81 Bode's galaxy; M82 Cigar galaxy; M83 Southern Pinwheel galaxy; M87 Virgo A; M97, Owl nebula; M101 Pinwheel galaxy; M104 Sombrero galaxy; M110 satellite galaxy of the Andromeda galaxy