Circinus (The Compasses) Sky Guide
Circinus IAU constellation (93 sq deg, rank 85): compact June southern constellation beside Alpha Centauri, led by +3.18 Alpha Circini and Circinus X-1.
Sky Navigation & Astrophysical Context
Covering only 93 square degrees immediately east-southeast of Alpha and Beta Centauri, Circinus is the fourth-smallest of the 88 IAU constellations. Introduced by Nicolas-Louis de Lacaille in 1756 as 'le Compas' to pair with neighboring Norma (the Carpenter's Square) and Triangulum Australe (the Surveyor's Level), its narrow V-shaped pair of legs mimics a drafting divider sitting in the rich Centaurus-Norma Milky Way.
The hinge of the Compasses is marked by Alpha Circini (V = +3.18), the brightest known rapidly oscillating Ap (roAp) chemically peculiar magnetic star in the sky, which exhibits non-radial acoustic p-mode pulsations with a period of just 6.8 minutes and is accompanied by a +8.5-magnitude K5 V orange dwarf companion 15.6 arcseconds away.
Despite its small footprint, Circinus hosts two major astrophysical landmarks: the Circinus Galaxy (ESO 97-G13), an active Seyfert 2 spiral galaxy only 4.2 megaparsecs (~13.7 million light-years) away that lies hidden 4° below the Galactic Plane and drives bipolar ionization cones, and Circinus X-1, a young runaway X-ray binary neutron star still embedded in its natal supernova remnant.
Equatorial Center Position & Transit Altitude
Circinus is centered near Right Ascension 14h 54m 36s, Declination −63° 01′ 48″ (The Drafting Compasses).
Practical Star-Hopping & Observing Tips
- Look just 4° south-southeast of brilliant Alpha Centauri (Rigil Kentaurus) to locate +3.18 Alpha Circini and the slender V of Beta and Gamma Circini.
- Split Alpha Circini in a 75 mm telescope at 80× to see the white A-type primary (+3.19) and its orange K5 V companion (+8.47) at 15.6 arcseconds.
- Sweep 3.5° northeast of Beta Circini to observe the compact 7th-magnitude open cluster NGC 5823 (Caldwell 88).
Notable Celestial Objects in & Near Circinus
| Object | Family | Classification | RA (J2000) | Dec (J2000) | Min. Instrument |
|---|---|---|---|---|---|
| Proxima Centauri (Nearest Star to Sun) | stars | Red dwarf flare star (nearest extrasolar star to the Sun) | 14h 29m 42.95s | -62° 40′ 46.1″ | 80–100 mm telescope with detailed finder chart (Southern Hemisphere / low northern latitudes) |
| Proxima Centauri b (Nearest Exoplanet) | exoplanets | Nearest known exoplanet (radial-velocity habitable-zone terrestrial candidate) | 14h 29m 42.95s | -62° 40′ 46.1″ | 80–100 mm telescope to view the 11.13-mag host star Proxima Centauri |
| Omega Centauri (NGC 5139 Cluster) | globular-clusters | Globular cluster / stripped dwarf galaxy nucleus | 13h 26m 47.24s | -47° 28′ 46.1″ | Naked eye (south of 35°N) |
Scientific Sources Cited
- IAU Official Constellation Boundaries & Designations (IAU 88 Recognized Constellations): Delporte, E. 1930, Délimitation scientifique des constellations (IAU / Cambridge University Press) — International Astronomical Union (IAU)
- SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg