Astronomers have inherited many useful concepts from antiquity. (2) For example, ancient mathematicians invented angles and a system of angular measure that is still used to denote the positions and apparent sizes of objects in the sky. (3) When we locate stars, we don’t need to know their distances from Earth (which are all different). (4) All we need to know is the angle from one star to another in the sky, a property that remains fixed over our lifetimes.
(Neil F. Comins and William J. Kaufmann III, Discovering the Universe)
Which word or phrase from the passage provides a context clue to help the reader understand the meaning of the word antiquity (sentence 1)?
useful
measure
the sky
ancient