Caelum the Sculptor's Chisel is a southern hemisphere constellation nestling between the older constellations of Columba the Dove and Eridanus the River. It is faint and nondescript as none of its stars are brighter than fourth magnitude. For northern observers it is best seen in the south at midnight during January, but from the latitudes of the British Isles only the northern half of the constellation rises above the horizon at that time.

Perhaps the easiest way to find this constellation is first to look for the much more prominent constellation of Orion the Hunter. Drop an imaginary line from Orion's red-giant, Betelgeuse, through the eastern side of Orion's belt, and continue southward through the length of the sword that hangs from it. Continue south through the constellation Lepus, past Sirius, the brightest star in the night sky, and stop short at about the same distance again. At this point you have arrived in the centre of Caelum near alpha Caeli, a total angular distance of 52 degrees. Other constellations it shares its border with are Dorado, Pictor and Horologium to its south, and with Lepus to its north. From a more southern viewpoint, Caelum is just 20 degrees north-east of Canopus, the second brightest star in the night sky, which is located in the nearby constellation of Carina.

Caelum occupies a relatively small and barren area of sky set apart from the Milky Way and has been described as more of a blank space than a constellation. Consequently it does not provide the star fields and clusters or nebulae that would otherwise provide points of interest for the amateur observer.

History

The shape of Caelum was first outlined by Abbé Nicolas Louis de la Caille while observing the far southern skies from the Cape of Good Hope, South Africa between 1750 and 1754. La Caille named the constellation 'Les Burins' after the 'burin' or graving tool used by artists to etch¹ wood or copper plate to produce a printed image. The word Caelum has a dual meaning in Latin. From classical Latin it is pronounced with a ‘hard’ K and means the burin, engraving tool or chisel that La Caille intended. In Vulgar or spoken Latin, with a softer ’s’ it means the 'sky' or the 'heavens' and is the origin from which the modern words celestial’ or ‘ceiling’ are derived.

On La Caille's star map of 1763, the image of a pair of crossed burins, tied at the centre with a ribbon and given the Latinised name of Caelum Scalptorium was first published. A later map and star list, Uranographia, of astronomer Johann Bode, added a pair of scribing tools to the image and identified it as Caela Scalptoris. The name eventually became shortened to Caelum.

La Caille formed a number of new constellations in that area of sky, to celebrate what was then the cutting edge of 18th Century art and technology. Most of his constellations were completely new and created to fill in the southernmost area that previously had been largely unseen and uncharted. One or two were created by appropriating stars from established constellations, and Caelum is one such case in that it occupies an area that was formerly part of Columba and the banks of the river Eridanus.

Unlike many other attempts by various astronomers, at forming constellations, most of La Caille's creations survived and became included in the International Astronomical Union's official list of 88 that are recognised today. In 1930 the IAU formalised the borders of the 88 constellations.

La Caille's other original constellations are:

• Antlia (Antlia Pneumatica, the Air Pump)
• Circinus, (Circinus, the pair of Compasses)
• Fornax (Fornax Chemica, the Chemical Furnace)
• Horologium (Horologium Oscillatorium, the Pendulum Clock)
• Mensa (Mons Mensae, the Table Mountain)
• Microscopium (Microscopium, the Microscope)
• Norma (Norma et Regula, the Level and Square)
• Octans (Octans Hadleianus, the Octant)
• Pictor (Equuleus Pictoris, the Painter's Easel)
• Pyxis (Pyxis Nautica, the Mariner's Compass)
• Reticulum (Reticulum Rhomboidalis, the Rhomboidal Net)
• Sculptor (L'Atelier du Sculpteur, the Sculptor's Studio)
• Telescopium (Telescopium or Tubus Astronomicus, the Telescope)

Principal Stars

The three stars beta, alpha and delta Caeli form a dog-legged line lying north to south in that order. Alpha Caeli is the brightest in this constellation but is only magnitude +4.43. It has a magnitude +12.3 companion with a separation of 10 arcseconds. Beta Caeli is a single F1 class star with a magnitude of +5.03. The third star in the asterism, delta Caeli is another single star with a magnitude of +5.06. Gamma Caeli is outside the asterism and lies exactly on the border with Columba. It is the second brightest star in this constellation.

Star Clusters, Nebulae and Galaxies

As previously noted, Caelum is a relatively barren patch of sky. La Caille must have been scraping the bottom of the barrel to find a space with enough stars to form another constellation and one has to wonder why he bothered. Being well away from the galactic plane there are no rich star fields or clusters, no nebulae or objects to excite the imagination within Caelum's confines. There is little to interest the amateur astronomer unless at some point in the future a supernova occurs, or a wandering star or comet moves across from another constellation, or some sharp-eyed astronomer finds another 'Voorwerp'
².

For the astronomer with larger aperture equipment there are 15 galaxies listed in the New General Catalogue, but none are brighter than magnitude +11.4. NGC 1679, a barred spiral galaxy is the brightest and is situated about two degrees south of zeta Caeli.

Meteor Showers and Extrasolar Planets

There are no meteor showers that have their apparent point of origin within Caelum. To date none of the stars within Caelum have been found to have extrasolar planets associated with them. No doubt there are some and their rarity is probably due more to the lack of research in that area of sky than their actual paucity.

Caelum in Modern Culture

One of the pleasures of astronomy is seeking out and looking first hand at some of the wonderful sights of the night sky. It is a sad fact that amateur telescopes in the hands of amateurs cannot usually bring out the detail and colour of those of the professional astronomer who has the equivalent of the Hubble Space Telescope available for use. The next best thing is the daily pleasure of the photographs made available through Astronomy Picture Of the Day. One of the contributors to APOD is Caelum Observatory, a commercial institution who regularly provides some of the most detailed pictures from observatories around the world.