| Minorplanet: | yes |
| 1085 Amaryllis | |
| Background: |
|
| Discovered: | 31 August 1927 |
| Mpc Name: | (1085) Amaryllis |
| Alt Names: | 1927 QH1964 CL A908 HBA915 QA A921 RC |
| Named After: | Amaryllis |
| Epoch: | 4 September 2017 (JD 2458000.5) |
| Uncertainty: | 0 |
| Observation Arc: | 109.40 yr (39,957 days) |
| Perihelion: | 3.0506 AU |
| Semimajor: | 3.1844 AU |
| Eccentricity: | 0.0420 |
| Period: | 5.68 yr (2,076 days) |
| Mean Motion: | / day |
| Inclination: | 6.6396° |
| Asc Node: | 139.98° |
| Arg Peri: | 127.53° |
| Dimensions: | km km km 69.68 km km km km |
| Rotation: | h h |
| Albedo: | 0.0437 |
| Abs Magnitude: | 9.409.709.89.81 |
1085 Amaryllis, provisional designation, is a background asteroid from the outer regions of the asteroid belt, approximately 69 kilometers in diameter. It was discovered on 31 August 1927, by astronomer Karl Reinmuth at the Heidelberg-Königstuhl State Observatory in southwest Germany. The asteroid was named after the flowering plant Amaryllis.
Amaryllis is a non-family asteroid from the main belt's background population. It orbits the Sun in the outer asteroid belt at a distance of 3.1–3.3 AU once every 5 years and 8 months (2,076 days). Its orbit has an eccentricity of 0.04 and an inclination of 7° with respect to the ecliptic.
The asteroid was first identified as at Taunton Observatory in April 1908. A few days later, the body's observation arc begins at the United States Naval Observatory in May 1908, or more than 19 years prior to its official discovery observation at Heidelberg.
Amaryllis has been characterized as an X-type asteroid by Pan-STARRS photometric survey. It is also an assumed carbonaceous C-type asteroid.
In March 2004, a first rotational lightcurve of Amaryllis was obtained from photometric observations by French amateur astronomer René Roy. Lightcurve analysis gave a rotation period of 18.2 hours with a brightness variation of 0.20 magnitude . In May 2016, the Spanish amateur astronomer group OBAS (Asteroid Observers, Spanish; Castilian: Observadores de Asteroids) measured a refined period of 18.111 hours with an amplitude of 0.19 magnitude .
According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Amaryllis measures between 65.55 and 72.93 kilometers in diameter and its surface has an albedo between 0.04 and 0.067.
The Collaborative Asteroid Lightcurve Link derives an albedo of 0.0437 and a diameter of 69.68 kilometers based on an absolute magnitude of 9.8.
This minor planet was named after the flowering planet Amaryllis, also known as belladonna lily, Jersey lily, naked lady, or amarillo. The official naming citation was mentioned in The Names of the Minor Planets by Paul Herget in 1955 .
Due to his many discoveries, Karl Reinmuth submitted a large list of 66 newly named asteroids in the early 1930s. The list covered his discoveries with numbers between and and also contained a sequence of 28 asteroids, starting with 1054 Forsytia, that were named after plants, in particular flowering plants (also see).