306 Unitas
Millosevich (1848–1919), a self-taught astronomer who became director of the Collegio Romano Observatory in Rome, discovered asteroid 303 Josephina on 12 February 1891 and asteroid 306 on 1 March of the same year.5 Tacchini named the new object Unitas, Latin for "unity," in honor of Angelo Pietro Secchi and also for the unity of Italy.5 • 7
| Key fact | Detail |
|---|---|
| Size and mass | Diameter 46.70 ± 2.3 km (IRAS); mass (5.33 ± 5.77) × 1017 kg1 |
| Rotation | 8.736 ± 0.001 hours, lightcurve amplitude 0.34 ± 0.02 magnitudes2 |
| Spectral type | S (Tholen and SMASSII); surface of low-Ca pyroxene and olivine3 |
| Hazard status | Not a near-Earth object and not classified as potentially hazardous; its orbit stays 0.99 AU from Earth's orbit at the closest point4 |
Orbit
Because the orbit never approaches Earth's, JPL has not classified Unitas as a potentially hazardous object, and orbital simulations show no close approaches to Earth.4
Physical characteristics
Radiometric measurements give a diameter of 46.70 ± 2.3 km with a geometric albedo of 0.2212 ± 0.023.1
Unitas rotates once every 8.736 hours, a period measured to a precision of a millisecond-scale fraction of an hour by Robert Koff at Antelope Hills Observatory from 2003–2004 photometry, with a brightness variation of 0.34 magnitudes over one rotation.2 That amplitude indicates a noticeably elongated or irregular shape.
Surface composition
Unitas is classified as an S-type asteroid in both the Tholen and SMASSII taxonomies, meaning a stony, silicate-rich surface.4 Near-infrared spectra (about 0.7 to 2.5 μm) obtained with the SpeX spectrograph at NASA's Infrared Telescope Facility suggest a surface with variable amounts of low-calcium pyroxene and olivine, and place Unitas in the S(IV) and S(VI) subtype regions of the Gaffey classification.3 The study, led by Paul S. Hardersen of the University of North Dakota with Michael J. Gaffey and colleagues, found that Unitas's band parameters are inconsistent with ordinary chondrite spectra, so it should not be considered a potential ordinary chondrite parent body; the spectra instead point to a surface that experienced at least partial melting at temperatures of roughly 950 °C or higher during the early Solar System.3
Relation to the Vesta family
Unitas's orbit falls within the region of the Vesta family, a large collisional family of V-type (basaltic) fragments associated with asteroid 4 Vesta.
Observation
Stellar occultations, in which the asteroid briefly hides a background star, provide size and shape constraints: a predicted occultation of a magnitude 9.7 star on 4 December 2026, with Unitas about 47 km across and 2.0 AU from Earth, was expected to produce a dimming of 3.5 magnitudes lasting about 1.9 seconds along the shadow's center line.6
References
- P. S. Hardersen et al., Near-infrared Reflectance Spectra... (Icarus 181, 2006), Table 2, ResearchGate
- Robert A. Koff, Lightcurve Photometry of Asteroids 306, 1508, 3223, 3270 and 3712, Minor Planet Bulletin 31 (2004)
- P. S. Hardersen et al., Near-infrared spectral observations and interpretations for S-asteroids 138 Tolosa, 306 Unitas, 346 Hermentaria, and 480 Hansa, Icarus 181 (2006), University of Arizona Experts
- Asteroid 306 Unitas (A891 EA), Space Reference
- Giuseppe Gullino, MILLOSEVICH, Elia, Dizionario Biografico degli Italiani, Volume 74 (2010), Treccani
- (306) Unitas hides a magnitude 9.7 star, 4 December 2026, Occult
- eclipse.gsfc.nasa.gov
Topic: Encyclopedia › Places and geography › Extraterrestrial places › Small bodies of the Solar System › Main-belt asteroids and numbered minor planets › Inner-belt asteroids › Asteroids named for virtues and abstract concepts
Initially written Oct 21, 2026 · Edited: Oct 25, 2026
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