Time smearing or time-average smearing is the degradation of the reconstructed image of a

celestial body An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical object, physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''bod ...

observed Observation is the active acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also involve the perception and recording of data (information), data via the use of scienti ...

by a ground-based

interferometer Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber op ...

that occurs because of the

duration Duration may refer to: * The amount of time elapsed between two events * Duration (music) – an amount of time or a particular time interval, often cited as one of the fundamental aspects of music * Duration (philosophy) – a theory of time and ...

of the observation. Unlike single

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observe ...

s or

camera A camera is an Optics, optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), ...

s that can compensate the Earth's rotation in real time with a dedicated

mount Mount is often used as part of the name of specific mountains, e.g. Mount Everest. Mount or Mounts may also refer to: Places * Mount, Cornwall, a village in Warleggan parish, England * Mount, Perranzabuloe, a hamlet in Perranzabuloe parish, C ...

, the different telescopes of the interferometer are at fixed positions on the Earth. As a result, maps obtained with interferometers feature the elongated orthoradial features similar to those of

night sky The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon. Natural light sources in a night sky include ...

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 Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The first detection of radio waves from an astronomical object was in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation coming f ...

, it severely limits the usable field of view of observations in very long baseline 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, , p. 247. Interferometry {{Astronomy-stub

See also

References