Editing Digit (unit) (section)

== Astronomy ==
In astronomy a digit is, or was until recently, one twelfth of the diameter of the sun or the moon.<ref name=11th/><ref name=chamb/> This is found in the [[Moralia]] of [[Plutarch]], XII:23,<ref name=plut/> but the definition as exactly one twelfth of the diameter may be due to [[Ptolemy]]. [[Sosigenes of Alexandria]] had observed in the 1st century AD that on a [[dioptra]], a disc with a diameter of 11 or 12 digits (of length) was needed to cover the moon.<ref name=neug/>

The unit was used in Arab or Islamic astronomical works such as those of [[Ṣadr al‐Sharīʿa al‐Thānī]] (d.1346/7),<ref name=hockey/> where it is called {{langx|ar|إصبعا}} ''iṣba' '', digit or finger.<ref name=sadr/>

The astronomical digit was in use in Britain for centuries. Heath, writing in 1760, explains that 12 digits are equal to the diameter in eclipse of the sun, but that 23 may be needed for the Earth's shadow as it eclipses the moon, those over 12 representing the extent to which the Earth's shadow is larger than the Moon.<ref name=heath/> The unit is apparently not in current use, but is found in recent dictionaries.<ref name=chamb/>