| Discovery[1] | |
|---|---|
| Discovered by | M. F. Wolf |
| Discovery site | Heidelberg Obs. |
| Discovery date | 14 January 1905 |
| Designations | |
| (555) Norma | |
| Pronunciation | Italian:[ˈnɔrma][2] |
Named after | Norma (character inBellini's opera)[3] |
| 1905 PT · 1928 FS 1939 BA · 1950 CC 1954 UH2 · 1968 HE1 | |
| main-belt · (outer) · background[4] | |
| Orbital characteristics[1] | |
| Epoch 4 September 2017 (JD 2458000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 112.20 yr (40,981 days) |
| Aphelion | 3.6636AU |
| Perihelion | 2.7105 AU |
| 3.1870 AU | |
| Eccentricity | 0.1495 |
| 5.69yr (2,078 days) | |
| 343.66° | |
| 0° 10m 23.52s / day | |
| Inclination | 2.6462° |
| 130.43° | |
| 356.51° | |
| Physical characteristics | |
| Dimensions | 27.89±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)[4] 40.11±1.5 km[11] |
| 19.508±0.002h[12] 19.55±0.01 h[13] 30.6±0.5 h[14] | |
| 0.0528(derived)[4] 0.0632±0.005[11] 0.08±0.02[10] 0.09±0.02[9] 0.0962±0.0150[8] 0.101±0.004[7] 0.119±0.018[5] | |
| SMASS =B[1] · B[9][15] C[4] | |
| 10.37±0.26[16] · 10.6[7][8][11] · 10.70[5][9] · 10.8[1][4][10] | |
555 Norma, provisional designation1905 PT, is a backgroundasteroid from the outer regions of theasteroid belt, approximately 33 kilometers in diameter. It was discovered on 14 January 1905, by German astronomerMax Wolf atHeidelberg Observatory in southwest Germany.[17] The asteroid was named after the title character of Bellini's operaNorma.[3]
Norma is abackground asteroid, located near the region occupied by theThemis family, a prominent family ofouter-belt asteroids with nearly coplanarecliptical 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 aneccentricity of 0.15 and aninclination of 3° with respect to the ecliptic.[1] The body'sobservation arc begins at Heidelberg in March 1911, more than six years after its official discovery observation.[17]
In theSMASS classification,Norma is aB-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 magnesiumpyroxenes based on data collected with theSubaru Telescope.[15]
In April 2007, a first rotationallightcurve ofNorma was obtained from photometric observations by French amateur astronomerPierre Antonini. Lightcurve analysis gave arotation period of 30.6 hours with a brightness variation of 0.2magnitude (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+), whileFrederick 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]
According to the surveys carried out by the Infrared Astronomical SatelliteIRAS, the JapaneseAkari satellite, and NASA'sWide-field Infrared Survey Explorer with its subsequentNEOWISE mission,Norma measures between 27.89 and 40.11 kilometers in diameter and its surface has analbedo of between 0.063 and 0.119.[5][6][7][8][9][10][11]
TheCollaborative Asteroid Lightcurve Link (CALL) agrees with IRAS, and derives an albedo of 0.0528 and a diameter of 40.02 kilometers based on anabsolute magnitude of 10.8. CALL also assumesNorma to be aC-type asteroid (rather than a B-type) due to its derived low albedo and the generalspectral type of the Themis family.[4]
Thisminor planet was named for the principal female character of the operaNorma by Italian composerVincenzo Bellini (1801–1835). In the opera, Norma is a high priestess of the Druids. In 1955, the official naming citation was published byPaul Herget inThe Names of the Minor Planets (H 59)[3]
