Caelum (the Chisel) is one of the smallest and faintest constellations in the southern sky. Introduced by French astronomer Nicolas-Louis de Lacaille during the 18th century, it represents an engraving tool rather than a figure from ancient mythology.
Its brightest star, Alpha Caeli, shines at only magnitude 4.4, making the constellation difficult to recognize without a star chart. Although Caelum contains few prominent deep-sky objects, it is home to an unusual quasar that once puzzled astronomers because its host galaxy could not be clearly detected.
Where Is Caelum and When Can You See It?
Caelum is the eighth-smallest of the 88 recognized constellations, covering approximately 125 square degrees of the southern sky. It lies south of Lepus, near Eridanus and Columba, with Dorado and Pictor farther south.
Caelum is best observed during December and January, particularly from the Southern Hemisphere. Its faint stars form a simple, inconspicuous pattern that is difficult to identify from light-polluted locations.
Who Created the Caelum Constellation?
Caelum was introduced in the 1750s by Nicolas-Louis de Lacaille, who mapped the southern sky while observing from the Cape of Good Hope in South Africa. He originally named it Caelum Scalptorium, referring to a sculptor’s or engraver’s chisel. The name was later shortened to Caelum.
Unlike the ancient Greek constellations, Caelum has no traditional mythology. It belongs to Lacaille’s group of southern constellations named after scientific instruments, tools, and other objects.
Notable Stars in Caelum
Caelum has no stars brighter than fourth magnitude, but several are interesting examples of different stellar types.
Image Credit: © Torsten Bronger Alpha Caeli – The constellation’s brightest star, a binary system approximately 66 light-years away with an apparent magnitude of 4.4. Its primary is a yellow-white F-type main-sequence star, accompanied by a much fainter red dwarf.
- Gamma Caeli – A multiple-star grouping approximately 185 light-years away, with its brightest component shining at magnitude 4.6. The prominent star is an orange giant that has expanded beyond the main sequence.
- Beta Caeli – A yellow-white star approximately 90 light-years away, shining at magnitude 5.0. It is hotter and more luminous than the Sun.
- Delta Caeli – A blue-white subgiant several hundred light-years away. Its high surface temperature gives it a noticeably different color from the cooler stars in the constellation.
Deep-Sky Objects in Caelum
Caelum lies away from the crowded plane of the Milky Way. It contains no Messier objects and relatively few bright deep-sky targets, although several distant galaxies can be observed with larger telescopes.
HE0450−2958 — The Quasar Without a Home
The most unusual object associated with Caelum is HE0450−2958, a distant quasar that attracted attention because astronomers initially struggled to identify its host galaxy.
A quasar is an extremely luminous active galactic nucleus, powered by material falling toward a supermassive black hole. Early observations with the Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope failed to reveal an obvious galaxy surrounding HE0450−2958, leading to its nickname, the quasar without a home.
A nearby companion galaxy was found to be undergoing intense star formation, raising questions about whether activity associated with the quasar was influencing its neighbor.
Later observations suggested that the quasar may have a faint or partially obscured host galaxy after all. The system remains an interesting example of the complicated relationship between supermassive black holes, galaxy interactions, and star formation.
Other Galaxies in Caelum
- NGC 1679 – A distant spiral galaxy with a relatively faint appearance, best suited to larger amateur telescopes and astrophotography.
- NGC 1571 – A galaxy of approximately 12th magnitude, making it a challenging target for visual observers.
- IC 2106 – A barred spiral galaxy located far beyond the Milky Way, whose structure is more readily revealed through long-exposure photography.
How to Find Caelum
Caelum lies between the better-known constellations Eridanus and Columba, south of Lepus. Begin by locating the brighter stars of Lepus beneath Orion, then use a detailed star chart to move south toward Caelum.
Because its stars are faint and widely spaced, Caelum is best observed under dark skies. For most amateur stargazers, identifying the constellation itself is more realistic than attempting to observe its distant galaxies.