Norma (minor planet designation: 555 Norma), provisional designation 1905 PT, is a background asteroid from the outer regions of the asteroid belt, approximately 33 kilometers in diameter. It was discovered on 14 January 1905, by German astronomer Max Wolf at Heidelberg Observatory in southwest Germany.[17] The asteroid was named after the title character of Bellini's opera Norma.[2]

555 Norma
Discovery [1]
Discovered byM. F. Wolf
Discovery siteHeidelberg Obs.
Discovery date14 January 1905
(555) Norma
PronunciationItalian: [ˈnɔrma][4]
Named after
(character in Bellini's opera)[2]
1905 PT · 1928 FS
1939 BA · 1950 CC
1954 UH2 · 1968 HE1
main-belt · (outer) · background[3]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc112.20 yr (40,981 days)
Aphelion3.6636 AU
Perihelion2.7105 AU
3.1870 AU
5.69 yr (2,078 days)
0° 10m 23.52s / day
Physical characteristics
Dimensions27.89±0.68 km[5]
31.040±0.150 km[6]
31.80±0.58 km[7]
32.541±0.215 km[8]
33±3 km[9]
33.0±3.3 km[10]
40.02 km (derived)[3]
40.11±1.5 km[11]
19.508±0.002 h[12]
19.55±0.01 h[13]
30.6±0.5 h[14]
0.0528 (derived)[3]
SMASS = B[1] · B[9][15]
10.37±0.26[16] · 10.6[7][8][11] · 10.70[5][9] · 10.8[1][3][10]

Classification and orbitEdit

Norma is a background asteroid, located near the region occupied by the Themis family, a prominent family of outer-belt asteroids with nearly coplanar ecliptical orbits. It orbits the Sun at a distance of 2.7–3.7 AU once every 5 years and 8 months (2,078 days). Its orbit has an eccentricity of 0.15 and an inclination of 3° with respect to the ecliptic.[1] The body's observation arc begins at Heidelberg in March 1911, more than six years after its official discovery observation.[17]

Physical characteristicsEdit

Spectral typeEdit

In the SMASS classification, Norma is a B-type asteroid. These types of asteroids have a featureless surface that displays magnesium-rich silicates, which likely accounts for the relatively high albedo as an outer-belt asteroid. Norma surface consists of more than 50% amorphous magnesium pyroxenes based on data collected with the Subaru Telescope.[15]


In April 2007, a first rotational lightcurve of Norma was obtained from photometric observations by French amateur astronomer Pierre Antonini. Lightcurve analysis gave a rotation period of 30.6 hours with a brightness variation of 0.2 magnitude (U=2).[14] However more recent observations by two American astronomers have since superseded this result.

In December 2011, Robert Stephens at the Santana Observatory (646) obtained a lightcurve that gave a period 19.55 hours and a brightness amplitude of 0.06 magnitude (U=2+), while Frederick Pilcher measured a period of 19.508 hours with an amplitude of 0.25 at the Organ Mesa Observatory (G50) in November 2016.[12][13]

Diameter and albedoEdit

According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite, and NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Norma measures between 27.89 and 40.11 kilometers in diameter and its surface has an albedo of between 0.063 and 0.119.[5][6][7][8][9][10][11]

The Collaborative Asteroid Lightcurve Link (CALL) agrees with IRAS, and derives an albedo of 0.0528 and a diameter of 40.02 kilometers based on an absolute magnitude of 10.8. CALL also assumes Norma to be a C-type asteroid (rather than a B-type) due to its derived low albedo and the general spectral type of the Themis family.[3]


This minor planet was named for the principal female character of the opera Norma by Italian composer Vincenzo Bellini (1801–1835). In the opera, Norma is a high priestess of the Druids. In 1955, the official naming citation was published by Paul Herget in The Names of the Minor Planets (H 59)[2]


  1. ^ a b c d e "JPL Small-Body Database Browser: 555 Norma (1905 PT)" (2017-03-29 last obs.). Jet Propulsion Laboratory. Retrieved 17 August 2017.
  2. ^ a b c Schmadel, Lutz D. (2007). "(555) Norma". Dictionary of Minor Planet Names – (555) Norma. Springer Berlin Heidelberg. p. 58. doi:10.1007/978-3-540-29925-7_556. ISBN 978-3-540-00238-3.
  3. ^ a b c d e f "LCDB Data for (555) Norma". Asteroid Lightcurve Database (LCDB). Retrieved 17 August 2017.
  4. ^ Norma (Dizionario Rai)
  5. ^ a b c d Masiero, Joseph R.; Mainzer, A. K.; Grav, T.; Bauer, J. M.; Cutri, R. M.; Nugent, C.; et al. (November 2012). "Preliminary Analysis of WISE/NEOWISE 3-Band Cryogenic and Post-cryogenic Observations of Main Belt Asteroids". The Astrophysical Journal Letters. 759 (1): 5. arXiv:1209.5794. Bibcode:2012ApJ...759L...8M. doi:10.1088/2041-8205/759/1/L8. Retrieved 17 August 2017.
  6. ^ a b Masiero, Joseph R.; Grav, T.; Mainzer, A. K.; Nugent, C. R.; Bauer, J. M.; Stevenson, R.; et al. (August 2014). "Main-belt Asteroids with WISE/NEOWISE: Near-infrared Albedos". The Astrophysical Journal. 791 (2): 11. arXiv:1406.6645. Bibcode:2014ApJ...791..121M. doi:10.1088/0004-637X/791/2/121. Retrieved 17 August 2017.
  7. ^ a b c d Usui, Fumihiko; Kuroda, Daisuke; Müller, Thomas G.; Hasegawa, Sunao; Ishiguro, Masateru; Ootsubo, Takafumi; et al. (October 2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan. 63 (5): 1117–1138. Bibcode:2011PASJ...63.1117U. doi:10.1093/pasj/63.5.1117. (online, AcuA catalog p. 153)
  8. ^ a b c d Mainzer, A.; Grav, T.; Masiero, J.; Hand, E.; Bauer, J.; Tholen, D.; et al. (November 2011). "NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results". The Astrophysical Journal. 741 (2): 25. arXiv:1109.6407. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90.
  9. ^ a b c d e Alí-Lagoa, V.; de León, J.; Licandro, J.; Delbó, M.; Campins, H.; Pinilla-Alonso, N.; et al. (June 2013). "Physical properties of B-type asteroids from WISE data". Astronomy and Astrophysics. 554: 16. arXiv:1303.5487. Bibcode:2013A&A...554A..71A. doi:10.1051/0004-6361/201220680.
  10. ^ a b c d Alí-Lagoa, V.; Licandro, J.; Gil-Hutton, R.; Cañ; ada-Assandri, M.; Delbo', M.; et al. (June 2016). "Differences between the Pallas collisional family and similarly sized B-type asteroids". Astronomy and Astrophysics. 591: 11. Bibcode:2016A&A...591A..14A. doi:10.1051/0004-6361/201527660. Retrieved 17 August 2017.
  11. ^ a b c d Tedesco, E. F.; Noah, P. V.; Noah, M.; Price, S. D. (October 2004). "IRAS Minor Planet Survey V6.0". NASA Planetary Data System. 12: IRAS-A-FPA-3-RDR-IMPS-V6.0. Bibcode:2004PDSS...12.....T. Retrieved 22 October 2019.
  12. ^ a b Pilcher, Frederick (April 2017). "Rotation Period Determination for 396 Aeolia, 298 Admete, 422 Berolina, and 555 Norma". The Minor Planet Bulletin. 44 (2): 112–114. Bibcode:2017MPBu...44..112P. ISSN 1052-8091. Retrieved 17 August 2017.
  13. ^ a b Stephens, Robert D. (April 2012). "Asteroids Observed from GMARS and Santana Observatories: 2011 October- December". The Minor Planet Bulletin. 39 (2): 80–82. Bibcode:2012MPBu...39...80S. ISSN 1052-8091. Retrieved 17 August 2017.
  14. ^ a b Behrend, Raoul. "Asteroids and comets rotation curves – (555) Norma". Geneva Observatory. Retrieved 17 August 2017.
  15. ^ a b Kasuga, Toshihiro; et al. (February 2015), "Near-Infrared Spectra of High-Albedo Outer Main-Belt Asteroids", The Astronomical Journal, 149 (2): 8, Bibcode:2015AJ....149...37K, doi:10.1088/0004-6256/149/2/37, 37.
  16. ^ Veres, Peter; Jedicke, Robert; Fitzsimmons, Alan; Denneau, Larry; Granvik, Mikael; Bolin, Bryce; et al. (November 2015). "Absolute magnitudes and slope parameters for 250,000 asteroids observed by Pan-STARRS PS1 - Preliminary results". Icarus. 261: 34–47. arXiv:1506.00762. Bibcode:2015Icar..261...34V. doi:10.1016/j.icarus.2015.08.007. Retrieved 17 August 2017.
  17. ^ a b "555 Norma (1905 PT)". Minor Planet Center. Retrieved 17 August 2017.

External linksEdit