What did the ancient Greeks determine that was the first step in understanding distances in the universe? - the distance from Athens to Rome - the diameter of the moon - Earth's circumference - the distance to the sun

the diameter of the moon

Explanation:

The first distance to be measured with any accuracy was that of the Moon. In the middle of the 2nd century BCE, Greek astronomer Hipparchus pioneered the use of a method known as parallax.

Historically, the first person to measure the distance to the sun was the Greek astronomer Aristarchus around the year 250 B. C. He used the phases of the moon to measure the sizes and distances of the sun and moon. During a half moon, the three celestial bodies should form a right angle.