(astronomy) 149,597,870,700 metres, the approximate mean distance from the Earth to the Sun (the semi-major axis of Earth's orbit), (symbol AU), used to measure distances in the solar system.

plural of astronomical unit

The time it takes the Earth to pass once around the Sun, particularly a tropical, sidereal, or anomalistic year.

The period in which the sun is between 12° and 18° below the horizon in the morning and evening.

plural of astronomical year

plural of astronomical transient

(astronomy) A localized discrete transient optical spectrum event at astronomical distances.

The time past mean noon of a particular day, reckoned on to twenty-four hours in mean time.

Synonym of atmospheric refraction

(Britain) An honorary title given to a leading astronomer; once the director of the Greenwich observatory.