adj. (also astronomic) 1 of or relating to astronomy. 2 extremely large; too large to contemplate. astronomical unit a unit of measurement in astronomy equal to the mean distance from the centre of the earth to the centre of the sun, 1.495 x 10(11) metres or 92.9 million miles. astronomical year see YEAR n. 1. astronomically adv.
[ L astronomicus f. Gk astronomikos ]