scan speed

The term scan speed is (I presume) the rate at which a telescope's direction is shifted to a new portion of the celestial sphere during an observation. I see it cited as an angle per second, e.g., 30"/s (30 arcseconds per second). The concept is relevant to surveys (e.g., slew surveys) and observations of extended targets, in both cases where the telescope's direction moved during the observation. There is presumed to be a tradeoff between the scan speed used and the quality of the observation, with the integration time also being a factor.

I presume a scan speed is generally used to indicate the angular distance shifted across the celestial sphere (per unit time), but I suppose it might cited in relation to the telescope's aim in relation to its mount, in which case the aim is further affected by the spacecraft's or (for a ground telescope) the Earth's rotation. For rapid scans, Earth rotation might make little contribution; on the celestial equator, it would affect the scan at a rate of 15"/s.

Some space telescopes and probes are designed to observe while (slowly) spinning, with a fixed scan speed.