Simplify the following text for a Grade 13 native English-speaking person.
Original: The Greek astronomer and astrologer Hipparchus ( 190-120 BCE ) created a table of chord functions giving the length of the chord for each angle , and there are references to his using polar coordinates in establishing stellar positions .
Simplified: The astronomer Hipparchus ( 190-120 BCE ) created a table of chord functions giving the length of the chord for each angle , and there are references to his using polar coordinates in establishing stellar positions .