Horologium
What is Horologium?
Constellations· Southern summer · a long strip south of Eridanus. Lacaille's tribute to the pendulum clock. A long chain of faint stars, notable for the wildly varying Mira-type star R Horologii and for the distant galaxy cluster in this direction.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where Horologium is in your sky right now: https://nowsky.org/solar/sky?sel=con:Horologium — location and time set automatically, no login.
Stars of the figure
| Star | Magnitude |
|---|---|
| Alpha Horologii | 3.9 |
The 1 brightest of the 2 stars used in the figure (1 lines). Lower magnitude means brighter.
Constellation basics
| Season | Nov–Jan evenings; not visible from Korea |
|---|---|
| Brightest star | α Horologii, mag 3.9 |
| How to find | east of Achernar, beside the southern end of Eridanus |
| Area rank | 58th of 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Frequently asked
- When can I see Horologium?
- Nov–Jan evenings; not visible from Korea.
- How do I find Horologium?
- east of Achernar, beside the southern end of Eridanus.
- What is the brightest star in Horologium?
- Alpha Horologii, magnitude 3.9.
- Where is Horologium in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
The supercluster behind the clock
About 700 million light-years away in the direction of Horologium lies the Horologium–Reticulum Supercluster, a gathering of dozens of galaxy clusters. Holding more than 30,000 galaxies and spanning over 500 million light-years, it ranks among the largest known superclusters, far heavier than our own Local Supercluster. On the sky it covers a region of about 12° across Horologium and Reticulum.
Superclusters are the largest structures bound by gravity in the universe, with empty voids between them. This one is among the best-studied large-scale structures in the southern sky, a knot in the cosmic web where clusters connect in threads. Beyond the dark sky of a constellation without a single 4th-magnitude star hangs the weight of tens of thousands of galaxies.
The constellation in depth
Horologium is one of the scientific-instrument constellations Lacaille added to the southern sky in the 1750s, honouring the pendulum clock invented by Huygens in the 17th century. Old charts show a tall clock with weights and a dial; the long line of stars suggested the shape. Alpha Horologii itself lies about 115 light-years from the Sun.
Alpha Horologii, its brightest star, is an orange giant of magnitude 3.9. The variable R Horologii swings from magnitude 4.7 to 14 over a period of about 400 days — a change of thousands of times in brightness, large even for a Mira-type star. The Horologium supercluster of galaxies, some 700 million light-years away, also lies in this direction. A telescope shows several of its galaxies, though none is bright.
At declinations of −40° to −67° it cannot be seen from Korea. From the southern hemisphere, find it on November to January evenings as a faint strip extending east of Achernar. In the Sky view, set Cape Town on a December evening and look beside the southern end of Eridanus. Because its stars are faint, keep the constellation lines switched on. Achernar makes a handy guide star for the search.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.