What did Eratosthenes measure to find the size of the Earth?

The angle of the Sun's shadow at two places a known distance apart

What did Aristarchus use the half Moon (first quarter) to estimate?

The relative distance of the Sun compared with the Moon

A slow conical wobble of the axis over about 26000 years

The Moon is between the Sun and the Earth

The Moon's orbit is tilted about 5 degrees, so the shadow usually misses

Red sunlight is refracted through the Earth's atmosphere into the shadow

The Moon is too far to cover the Sun, leaving a bright ring

The Moon is fully inside the umbra (start of totality)

12questions. Pick an answer and you'll see why right away.

What did Eratosthenes measure to find the size of the Earth?
A shadow angle of 7.2 degrees is found between cities 800 km apart. What is the Earth's circumference?
What did Aristarchus use the half Moon (first quarter) to estimate?
When do spring tides occur?
Which body has the larger effect on the tides?
What is the precession of the Earth's axis?
During a total solar eclipse, what is the arrangement of the bodies?
Why does an eclipse not happen at every new Moon?
Why does a totally eclipsed Moon often appear red?
What is an annular solar eclipse?
What does second umbral contact mark during an eclipse?
About how many times further away is the Sun than the Moon?