Caelum
What is Caelum?
Constellations· Southern summer · a gap between Eridanus and Columba. Caelum is Lacaille's tribute to the engraver's chisel. It is the eighth-smallest of the 88 constellations, and its brightest stars are two of fourth magnitude, making it one of the least noticeable in the sky.
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Stars of the figure
| Star | Magnitude |
|---|---|
| Alpha Caeli | 4.4 |
The 1 brightest of the 3 stars used in the figure (2 lines). Lower magnitude means brighter.
Constellation basics
| Season | Dec–Jan evenings; low in the south from New York; only its northern part from London |
|---|---|
| Brightest star | α Caeli, mag 4.4 |
| How to find | southwest of Lepus, west of Columba |
| Area rank | 81st of 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
The puzzle of the quasar without a galaxy, toward Caelum
A quasar is a very bright object powered by a giant black hole at the centre of a galaxy as it swallows surrounding matter. So every quasar should sit inside a galaxy. Yet in 2005 astronomers reported that around the quasar HE 0450-2958, about five billion light-years away in the direction of Caelum, no galaxy could be found.
Neither the Hubble Space Telescope nor ESO's Very Large Telescope showed a clear sign of one. Some even suggested it might be a black hole drifting alone without a galaxy, and it was nicknamed the naked quasar. It drew great interest because it seemed to break the idea that black holes and galaxies grow up together.
Later observations revealed a galaxy right next to the quasar where new stars were forming rapidly. Explanations followed: perhaps the quasar was flung out after colliding with that galaxy, or its own host galaxy was so small and dim that it was lost in the glare. In 2009 a study reported that material blasted from the quasar was helping to trigger star formation in the neighbouring galaxy.
The constellation in depth
Caelum was placed by Lacaille in the 1750s in an empty patch of the southern sky. The name he first gave it was the French word for burins, the chisels used to engrave pictures into copper plates. Old star maps show two such tools crossed over each other. Its Latin name was later shortened to Caelum.
Caelum is small and has no bright stars. Its brightest star, Alpha Caeli, is a white star of magnitude 4.4 about 66 light-years away. It has a faint red dwarf as a companion. Gamma Caeli splits into two stars in a small telescope. Lying far from the Milky Way, Caelum also has almost no notable star clusters or nebulae.
So Caelum is easier to find using its neighbours than by its own shape. First find Lepus, below Orion, and Columba to its south, then join the two faint stars to the west of them. Caelum sits inside the bend where the stars of Eridanus curve around. The short line between those two stars is the chisel itself.
From mid-northern latitudes such as New York it rises low above the southern horizon on December and January nights, and it can only be picked out from a dark site with an open view to the south. From the southern hemisphere, go south from Orion past Lepus and Columba on a summer evening. In the Sky view, set Sydney on a January evening and switch on the constellation lines to see where it is.
Frequently asked
- When can I see Caelum?
- Caelum is best seen in Dec–Jan evenings; low in the south from New York; only its northern part from London.
- How do I find Caelum?
- To find Caelum, look for southwest of Lepus, west of Columba.
- What is the brightest star in Caelum?
- The brightest star in Caelum is Alpha Caeli, at magnitude 4.4.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.