| Minorplanet: | yes |
| Background: |
|
| 991 McDonalda | |
| Mpc Name: | (991) McDonalda |
| Alt Names: | 1922 NB, 1949 PF, 1950 WG, 1953 GT1, 1975 EE6 |
| Discoverer: | O. Struve |
| Discovery Site: | Williams Bay |
| Discovered: | 24 October 1922 |
| Orbit Ref: | [1] |
| Observation Arc: | 80.10 yr (29255 days) |
| Uncertainty: | 0 |
| Epoch: | 31 July 2016 (JD 2457600.5) |
| Eccentricity: | 0.15791 |
| Semimajor: | 3.1419AU |
| Perihelion: | 2.6458AU |
| Aphelion: | 3.6381abbr=onNaNabbr=on |
| Period: | 5.57 yr (2034.2 d) |
| Inclination: | 2.0696° |
| Asc Node: | 63.255° |
| Arg Peri: | 254.682° |
| Mean Anomaly: | 351.48° |
| Abs Magnitude: | 11.12 |
| Spectral Type: | C |
| Mean Motion: | / day |
| Mean Radius: | km |
991 McDonalda is a Themistian asteroid. It was discovered by Otto Struve in 1922 at the Yerkes Observatory in Williams Bay, Wisconsin, United States. It is named after the McDonald Observatory, which Struve helped found in 1939.[2]