Time smearing

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.

Key Details of Time Smearing

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.

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.

See also

• Radio astronomy#Radio interferometry
• Radio telescope#Radio interferometry

References

• Bridle, Alan H. and Schwab, Frederic R., Wide Field Imaging I: Bandwidth and Time-Average Smearing in Synthesis imaging in radio astronomy (1989), eds. Richard A. Perley, Frederic R. Schwab, Astronomical Society of the Pacific Conference Series, vol. 6, ISBN 0-937707-23-6, p. 247.