Star position in the context of Celestial equator

A star catalogue is an astronomical catalogue that lists stars. In astronomy, many stars are referred to simply by catalogue numbers. There are a great many different star catalogues which have been produced for different purposes over the years, and this article covers only some of the more frequently quoted ones. Star catalogues were compiled by many different ancient people, including the Babylonians, Greeks, Chinese, Persians, and Arabs. They were sometimes accompanied by a star chart for illustration. Most modern catalogues are available in electronic format and can be freely downloaded from space agencies' data centres. The largest is being compiled from the spacecraft Gaia and thus far has over a billion stars.

Completeness and accuracy are described by the faintest limiting magnitude V (largest number) and the accuracy of the positions.

In astronomy, a transit instrument is a small telescope with an extremely precisely graduated mount used for the precise observation of star positions. They were previously widely used in astronomical observatories and naval observatories to measure star positions in order to compile nautical almanacs for use by mariners for celestial navigation, and observe star transits to set extremely accurate clocks (astronomical regulators) which were used to set marine chronometers carried on ships to determine longitude, and as primary time standards before atomic clocks. The instruments can be divided into three groups: meridian, zenith, and universal instruments.

A nocturnal is an instrument used to determine the local time based on the position of a star in the night sky relative to the pole star. As a result of the Earth's rotation, any fixed star makes a full revolution around the pole star in 23 hours and 56 minutes and therefore can be used as an hour hand. The 4-minute difference between the solar day and sidereal day requires a correction of this giant clock based on the date of observation, and nocturnal helps to apply this correction.

Sometimes called a horologium nocturnum (time instrument for night) or nocturlabe (in French and occasionally used by English writers), it is related to the astrolabe and sundial. Knowing the time is important in piloting for calculating tides and some nocturnals incorporate tide charts for important ports.