| Minorplanet: | yes |
| Background: |
|
| 120 Lachesis | |
| Discovered: | 10 April 1872 |
| Mpc Name: | (120) Lachesis |
| Alt Names: | A872 GB; 1910 CF; 1918 UB |
| Pronounced: | [1] |
| Adjective: | Lachesian |
| Epoch: | 31 July 2016 (JD 2457600.5) |
| Semimajor: | 3.11767AU |
| Perihelion: | 2.9539AU |
| Aphelion: | 3.2814abbr=onNaNabbr=on |
| Eccentricity: | 0.052528 |
| Period: | 5.50 yr (2010.7 d) |
| Inclination: | 6.9643° |
| Asc Node: | 341.193° |
| Arg Peri: | 232.822° |
| Avg Speed: | 16.86 km/s |
| Mass: | 5.5 kg |
| Surface Grav: | 0.0487 m/s2 |
| Escape Velocity: | 0.0920 km/s |
| Rotation: | 46.551abbr=onNaNabbr=on |
| Abs Magnitude: | 7.75 |
| Mean Motion: | / day |
| Observation Arc: | 143.70 yr (52485 d) |
| Uncertainty: | 0 |
| Moid: | 1.95464AU |
| Jupiter Moid: | 1.72275AU |
| Tisserand: | 3.204 |
120 Lachesis is a large main-belt asteroid. It was discovered by French astronomer Alphonse Borrelly on April 10, 1872, and independently by German-American astronomer Christian Heinrich Friedrich Peters on April 11, 1872, then named after Lachesis, one of the Moirai, or Fates, in Greek mythology. A Lachesean occultation of a star occurred in 1999 and was confirmed visually by five observers and once photoelectrically, with the chords yielding an estimated elliptical cross-section of .
This body is orbiting the Sun with a period of 5.50 years and an eccentricity (ovalness) of 0.05. The orbital plane is inclined by 7° to the plane of the ecliptic. Photometric observations of this asteroid were made in early 2009 at the Organ Mesa Observatory in Las Cruces, New Mexico. The resulting light curve shows a synodic rotation period of 46.551 ± 0.002 hours with a brightness variation of 0.14 ± 0.02 in magnitude. It is a very slow rotator with the longest rotation period of an asteroid more than 150 km in diameter. As a primitive C-type asteroid it is probably composed of carbonaceous material.