Editing Observational astronomy (section)

=== Micrometer ===
The position or cross-wire [[Micrometer (device)|micrometer]] is an implement that has been used to measure [[double star]]s. This consists of a pair of fine, movable lines that can be moved together or apart. The telescope lens is lined up on the pair and oriented using position wires that lie at right angles to the star separation. The movable wires are then adjusted to match the two star positions. The separation of the stars is then read off the instrument, and their true separation determined based on the magnification of the instrument.