(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.

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

plural of astronomical unit

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

A person who studies radio astronomy.

plural of radio astronomer

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.