Question

which significant observation led the greeks to accept the idea that earth was a sphere? a. the shape of earth’s shadow on the moon during a lunar eclipse was always circular. b. the shape of the eclipse shadow on earth during a solar eclipse was always circular. c. the shape of the darkening across the sun’s disk during a solar eclipse always appeared circular. d. the sun disappears below one horizon each day and reappears above the opposite horizon.

Explanation:

To determine which observation led the Greeks to accept Earth as a sphere, we analyze each option:

• Option a: During a lunar eclipse, Earth's shadow on the Moon is always circular. A circular shadow implies the object (Earth) casting it is spherical, as only a sphere would cast a circular shadow from all angles.
• Option b: A solar eclipse's shadow on Earth is from the Moon, not related to Earth's shape.
• Option c: The darkening of the Sun's disk during a solar eclipse relates to the Moon's position, not Earth's shape.
• Option d: The Sun's daily rise/set is about Earth's rotation, not its shape.

So the key observation is Earth's circular shadow on the Moon during lunar eclipses.

Answer:

a. The shape of Earth’s shadow on the Moon during a lunar eclipse was always circular.