| Field | Astronomy, Radio astronomy, Interferometry | |
|---|---|---|
| Description | Degradation of interferometric images due to prolonged observation duration. | |
| Causes | Fixed telescope positions that cannot adjust for Earth's rotation. | |
| Effects | Elongated orthoradial features; limits the usable field of view in Very Long Baseline Interferometry. | |
| Mitigation | Using shorter integration times or specialized mounts. |
Time smearing or time-average smearing is the degradation of the reconstructed image of a celestial body observed by a ground-based interferometer that occurs because of the duration of the observation. Unlike single telescopes or cameras that can compensate for the Earth's rotation in real time using a dedicated mount, the different telescopes of the interferometer are at fixed positions on the Earth. As a result, maps obtained with interferometers feature elongated orthoradial features similar to those of night sky photographs taken with a fixed tripod, unless they use short enough integration times.
The smearing is a problem for long integration times or very separated telescopes. Mostly an issue in radioastronomy, it severely limits the usable field of view of observations in very long baseline interferometry.