Sextans (The Sextant) & Spindle Galaxy
Sextans IAU constellation (314 sq deg, rank 47): April equatorial constellation south of Regulus, led by +4.48 Alpha Sextantis and Spindle Galaxy NGC 3115.
Sky Navigation & Astrophysical Context
Straddling the celestial equator across a 314-square-degree rhombus tucked between the front paws of Leo (Regulus) to the north and the coils of Hydra (Alphard) to the south, Sextans was created by Johannes Hevelius in 1687 as 'Sextans Uraniae' (the Astronomical Sextant). Hevelius placed the fiery instrument between the Lion and the Water Snake to commemorate his favorite six-foot brass sextant, which had been destroyed when a catastrophic fire burned down his Danzig (Gdańsk) observatory on September 26, 1679.
Its brightest star, Alpha Sextantis (V = +4.48), is an A0 III horizontal-branch giant at 87 parsecs that functions as an unofficial 'equatorial pole star': sitting just 42.6 arcminutes south of the J2000.0 celestial equator, axial precession carried it from the northern celestial hemisphere into the southern hemisphere in December 1923.
For deep-sky observers, southwestern Sextans boasts the Spindle Galaxy (NGC 3115 / Caldwell 53, V = +9.1)—an edge-on S0 lenticular galaxy at 9.7 megaparsecs that shines several times brighter than the faint stars of Sextans around it and harbors one of the nearest billion-solar-mass supermassive black holes (~1–2 × 10⁹ M☉). Because of its clean extragalactic sightline, a 2-square-degree patch of Sextans was also chosen for the Hubble/Spitzer/Chandra/JWST COSMOS (Cosmic Evolution Survey) field, alongside the Local Group dwarf galaxies Sextans A, Sextans B, and the Sextans Dwarf Spheroidal.
Equatorial Center Position & Transit Altitude
Sextans is centered near Right Ascension 10h 16m 12s, Declination −02° 39′ 00″ (The Astronomical Sextant).
Practical Star-Hopping & Observing Tips
- Drop 12° directly south from Regulus (Alpha Leonis) to find the equatorial star Alpha Sextantis (+4.48).
- Aim a 100 mm+ telescope 5° northwest of Gamma Hydrae (or midway between Alpha Hydrae and Regulus, then south) to see the bright, sharp-tipped needle of the Spindle Galaxy (NGC 3115, V = +9.1).
- Use a 200 mm+ telescope under dark skies 1.5° southeast of Alpha Sextantis to spot the square-shaped Local Group irregular dwarf galaxy Sextans A.
Notable Celestial Objects in & Near Sextans
| Object | Family | Classification | RA (J2000) | Dec (J2000) | Min. Instrument |
|---|---|---|---|---|---|
| K2-18 b (Temperate Sub-Neptune in Leo) | exoplanets | Temperate sub-Neptune exoplanet with methane- and CO2-rich H2 atmosphere | 11h 30m 14.52s | +07° 35′ 18.2″ | 200–250 mm telescope to visually spot the 13.50-mag host star K2-18 |
| Sombrero Galaxy (Messier 104 / NGC 4594) | galaxies | Unbarred early-type spiral / lenticular-halo galaxy with edge-on dust ring | 12h 39m 59.43s | -11° 37′ 23.0″ | 60–80 mm telescope (150 mm+ to clearly trace the dark equatorial dust lane) |
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