| Minorplanet: | yes |
| Background: |
|
| 999 Zachia | |
| Mpc Name: | (999) Zachia |
| Alt Names: | 1923 NW |
| Discovered: | 9 August 1923 |
| Orbit Ref: | [1] |
| Observation Arc: | 92.68 yr (33850 days) |
| Uncertainty: | 0 |
| Epoch: | 31 July 2016 (JD 2457600.5) |
| Eccentricity: | 0.21704 |
| Semimajor: | 2.6118AU |
| Perihelion: | 2.045AU |
| Aphelion: | 3.1787abbr=onNaNabbr=on |
| Period: | 4.22 yr (1541.8 d) |
| Inclination: | 9.7603° |
| Asc Node: | 214.972° |
| Arg Peri: | 128.034° |
| Mean Motion: | / day |
| Abs Magnitude: | 10.8 |
| Rotation: | 22.77abbr=onNaNabbr=on |
| Mean Radius: | 8.95 km |
999 Zachia is a main-belt asteroid that was discovered by German astronomer Karl W. Reinmuth in 1923 and named after Hungarian astronomer Franz Xaver von Zach.
Photometric observations of this asteroid collected during 1999 show a rotation period of 22.77 ± 0.03 hours with a brightness variation of 0.3 magnitude.