Equuleus (The Little Horse) Sky Guide
Equuleus IAU constellation (72 sq deg, rank 87): second-smallest constellation, culminating in September beside Pegasus with +3.92 Kitalpha (Alpha Equ).
Sky Navigation & Astrophysical Context
At just 72 square degrees, Equuleus is the smallest constellation in the Northern Hemisphere and the second-smallest of all 88 IAU constellations (larger only than Crux at 68 square degrees). Cataloged by Ptolemy in the Almagest, this miniature trapezoid of fourth- and fifth-magnitude stars sits tucked between the nose of Pegasus (Enif) to the east and the diamond of Delphinus to the northwest, portraying the foal Celeris or the brother of the winged horse Pegasus.
Its brightest star is Kitalpha (Alpha Equulei, from the Arabic 'Qit'at al-Faras' meaning 'Part of the Horse,' V = +3.92), a well-studied composite spectroscopic and interferometric binary at 58 parsecs consisting of a G7 III yellow giant and an A4 V main-sequence star orbiting every 98.8 days.
Although lacking bright Messier objects, Equuleus rewards double-star enthusiasts with two classic tests at the northern corners of its trapezoid: Gamma Equulei (+4.69, a rapidly oscillating Ap star paired with +5.9-magnitude 6 Equulei 6 arcminutes away) and Epsilon Equulei (1 Equulei), a tight quadruple system where an close sub-arcsecond binary is accompanied by a +7.1-magnitude third component at 10.6 arcseconds.
Equatorial Center Position & Transit Altitude
Equuleus is centered near Right Ascension 21h 10m 48s, Declination +07° 45′ 36″ (The Little Horse (Foal)).
Practical Star-Hopping & Observing Tips
- Sweep 7° west-southwest from Enif (Epsilon Pegasi, the bright nose of Pegasus) to find the compact four-star trapezoid of Alpha, Beta, Gamma, and Delta Equulei.
- Use binoculars on Gamma Equulei to split its wide optical companion 6 Equulei (+6.07) separated by 5.6 arcminutes.
- In a 100 mm telescope at 120×, split Epsilon Equulei (the southwestern star of the foal) to see its +7.1-magnitude tertiary star 10.6 arcseconds east.
Notable Celestial Objects in & Near Equuleus
| Object | Family | Classification | RA (J2000) | Dec (J2000) | Min. Instrument |
|---|---|---|---|---|---|
| 51 Pegasi b (Dimidium First Hot Jupiter) | exoplanets | Prototype Hot Jupiter exoplanet orbiting a Sun-like G2 IV-V star | 22h 57m 27.98s | +20° 46′ 07.8″ | Naked eye under dark skies; 7×50 binoculars to view host star 51 Pegasi (V = 5.49) |
| Altair (Alpha Aquilae Rapid Rotator) | stars | Rapidly rotating A-type main-sequence star (Delta Scuti variable) | 19h 50m 47.00s | +08° 52′ 06.0″ | Naked eye |
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