| Discovery[1] | |
|---|---|
| Discovered by | M. F. Wolf |
| Discovery site | Heidelberg Obs. |
| Discovery date | 31 March 1916 |
| Designations | |
| (821) Fanny | |
Named after | unknown[2] |
| A916 GH · 1930 HC 1930 HO · 1930 HT 1916 ZC | |
| Orbital characteristics[3] | |
| Epoch 31 May 2020 (JD 2459000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 103.84yr (37,928 d) |
| Aphelion | 3.3602AU |
| Perihelion | 2.1833 AU |
| 2.7718 AU | |
| Eccentricity | 0.2123 |
| 4.61 yr (1,686 d) | |
| 150.41° | |
| 0° 12m 48.96s / day | |
| Inclination | 5.3989° |
| 209.76° | |
| 32.862° | |
| Physical characteristics | |
821 Fanny (prov. designation:A916 GHor1916 ZC) is a darkbackground asteroid andslow rotator from the central regions of theasteroid belt. It was discovered on 31 March 1916, by German astronomerMax Wolf at theHeidelberg-Königstuhl State Observatory in southwest Germany.[1] The carbonaceousC-type asteroid (Ch) has an exceptionally longrotation period of 236.6 hours and measures approximately 29 kilometers (18 miles) in diameter. Any reference of the asteroid's name to a person is unknown.[2]
Fanny is a non-family asteroid of the main belt'sbackground population when applying thehierarchical clustering method to itsproper orbital elements.[4][5][12] It orbits the Sun in thecentral asteroid belt at a distance of 2.2–3.4 AU once every 4 years and 7 months (1,686 days;semi-major axis of 2.77 AU). Its orbit has aneccentricity of 0.21 and aninclination of 5° with respect to theecliptic.[3] The body'sobservation arc begins at theHeidelberg Observatory on 1 April 1916, with its first recorded observation, the night after its official discovery.[1]
Any reference of thisminor planet's name to a person or occurrence is unknown.[2]
Among the many thousands ofnamed minor planets,Fanny is one of 120 asteroids for which no official naming citation has been published. All of these asteroids have low numbers, the first being164 Eva. The last asteroid with a name of unknown meaning is1514 Ricouxa. They were discovered between 1876 and the 1930s, predominantly by astronomersAuguste Charlois,Johann Palisa,Max Wolf andKarl Reinmuth.[13]
In theTholen classification and in theSDSS-based taxonomy,Fanny is a common, carbonaceousC-type asteroid.[5][11] In the Bus–BinzelSMASS classification, it is a hydrated carbonaceous Ch-subtype.[5]
In 2018, from April to June, a rotationallightcurve ofFanny was obtained fromphotometric observations over 46 nights byFrederick Pilcher at the Organ Mesa Observatory (G50) in New Mexico. Analysis gave a bimodal lightcurve with arotation period of236.6±0.3 hours and a brightness variation of0.22±0.03magnitude (U=3−).[10] This determination was adopted by theLightcurve Data base and accounts for Pilcher's observations taken between April and May. For observations taken between May and June, a similar period of230.6±0.3 hours with a somewhat higher amplitude of0.28±0.03 magnitude was derived (U=3−). The observer also ruled out non-principal axis rotation ("tumblin"), and considers a double period 470 hours as very unlikely.[10][a] This makes it aslow rotator, as most asteroids have much shorter periods between 2 and 20 hours. As of 2020[update],Fanny ranks among the250th slowest rotator known to exist.
During the same apparition,Tom Polakis at the Command Module Observatory (V02) in Arizona obtained a somewhat longer period of238.9±0.8 hours with a brightness variation of0.24±0.03 magnitude (U=2).[14] The result supersedes an incorrect period of5.44±0.05 hours with an amplitude of0.01 magnitude from a tentative one-night observation by French amateur astronomers Paul Krafft, Olivier Gerteis, Hubert Gully, Luc Arnold and Matthieu Bachschmidt from 2013 (U=1).[15]
According to the surveys carried out by the JapaneseAkari satellite and theNEOWISE mission of NASA'sWide-field Infrared Survey Explorer (WISE),Fanny measures (28.77±1.00) and (28.856±0.168) kilometers in diameter and its surface has analbedo of (0.040±0.003) and (0.038±0.013), respectively.[7][8][6] TheCollaborative Asteroid Lightcurve Link assumes a standard albedo for a carbonaceous C-type asteroid of 0.057 and calculates a diameter of 23.86 kilometers based on anabsolute magnitude of 11.84.[9] Alternative mean-diameter measurements published by the WISE team include (30.650±0.367 km), (31.50±8.89 km), (32.42±9.57 km) and (35.82±0.35 km) with corresponding albedos of (0.0345±0.0069), (0.03±0.03), (0.03±0.02) and (0.025±0.004).[5][9]
