# 306 Unitas
Millosevich (1848–1919), a self-taught astronomer who became director of the Collegio Romano Observatory in Rome, discovered asteroid [303 Josephina](https://www.edgepedia.org/303-josephina) on 12 February 1891 and asteroid 306 on 1 March of the same year.[5](https://www.treccani.it/enciclopedia/elia-millosevich_%28Dizionario-Biografico%29/) Tacchini named the new object Unitas, Latin for "unity," in honor of Angelo Pietro Secchi and also for the unity of Italy.[5](https://www.treccani.it/enciclopedia/elia-millosevich_%28Dizionario-Biografico%29/) • [7](https://eclipse.gsfc.nasa.gov/SENL/SENL200303.pdf)
| Key fact | Detail |
|---|---|
| Size and mass | Diameter 46.70 ± 2.3 km (IRAS); mass (5.33 ± 5.77) × 1017 kg[1](https://www.researchgate.net/publication/253442126_Near-infrared_Reflectance_Spectra_Of_135_Hertha_224_Oceana_516_Amherstia_And_872_Holda) |
| Rotation | 8.736 ± 0.001 hours, lightcurve amplitude 0.34 ± 0.02 magnitudes[2](https://www.yumpu.com/en/document/view/7939009/the-minor-planet-bulletin-minorplanetinfo/10) |
| Spectral type | S (Tholen and SMASSII); surface of low-Ca pyroxene and olivine[3](https://experts.arizona.edu/en/publications/near-infrared-spectral-observations-and-interpretations-for-s-ast/) |
| 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 point[4](https://www.spacereference.org/asteroid/306-unitas-a891-ea) |
## 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](https://www.spacereference.org/asteroid/306-unitas-a891-ea)
## Physical characteristics
Radiometric measurements give a diameter of 46.70 ± 2.3 km with a geometric albedo of 0.2212 ± 0.023.[1](https://www.researchgate.net/publication/253442126_Near-infrared_Reflectance_Spectra_Of_135_Hertha_224_Oceana_516_Amherstia_And_872_Holda)
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](https://www.yumpu.com/en/document/view/7939009/the-minor-planet-bulletin-minorplanetinfo/10) That amplitude indicates a noticeably elongated or irregular shape.
## Surface composition
Unitas is classified as an [S-type asteroid](https://www.edgepedia.org/s-type-asteroid) in both the Tholen and SMASSII taxonomies, meaning a stony, silicate-rich surface.[4](https://www.spacereference.org/asteroid/306-unitas-a891-ea) 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](https://experts.arizona.edu/en/publications/near-infrared-spectral-observations-and-interpretations-for-s-ast/) The study, led by Paul S. Hardersen of the [University of North Dakota](https://www.edgepedia.org/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](https://www.edgepedia.org/solar-system).[3](https://experts.arizona.edu/en/publications/near-infrared-spectral-observations-and-interpretations-for-s-ast/)
## Relation to the Vesta family
Unitas's orbit falls within the region of the [Vesta family](https://www.edgepedia.org/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](https://occult.alokm.com/asteroid?e=2026-12-04-306-unitas-099648)
## References
1. [P. S. Hardersen et al., Near-infrared Reflectance Spectra... (Icarus 181, 2006), Table 2, ResearchGate](https://www.researchgate.net/publication/253442126_Near-infrared_Reflectance_Spectra_Of_135_Hertha_224_Oceana_516_Amherstia_And_872_Holda)
2. [Robert A. Koff, Lightcurve Photometry of Asteroids 306, 1508, 3223, 3270 and 3712, Minor Planet Bulletin 31 (2004)](https://www.yumpu.com/en/document/view/7939009/the-minor-planet-bulletin-minorplanetinfo/10)
3. [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](https://experts.arizona.edu/en/publications/near-infrared-spectral-observations-and-interpretations-for-s-ast/)
4. [Asteroid 306 Unitas (A891 EA), Space Reference](https://www.spacereference.org/asteroid/306-unitas-a891-ea)
5. [Giuseppe Gullino, MILLOSEVICH, Elia, Dizionario Biografico degli Italiani, Volume 74 (2010), Treccani](https://www.treccani.it/enciclopedia/elia-millosevich_%28Dizionario-Biografico%29/)
6. [(306) Unitas hides a magnitude 9.7 star, 4 December 2026, Occult](https://occult.alokm.com/asteroid?e=2026-12-04-306-unitas-099648)
7. [eclipse.gsfc.nasa.gov](https://eclipse.gsfc.nasa.gov/SENL/SENL200303.pdf)
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*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*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license