This Is What Lunar Eclipses Can Teach Us About The Universe
“By looking at the sky alone, we can see the apparent, angular sizes of the Sun and Moon.
But when the Sun, Earth, and Moon all align to produce a total eclipse, it teach us how far astronomical distances truly are.
During a lunar eclipse, the Earth’s shadow falls on the Moon…”
If you wanted to learn the distances to the stars, you have to start closer: with distances and length scales you can measure before reaching for the heavens. During a total lunar eclipse, we can get there! We can not only determine the shape of the Earth, but also the Earth-Moon distance and the size of the Moon. With a little bit of care in our measurements, we can know the Earth-Sun distance and the size of the Sun, too, and this gives us a calibration point to reach for the stars. Simply by looking at relative brightness or, for more accurate results, a parallax measurement, we can learn the distance to astronomical objects beyond our Solar System.