There is a very cool pic on Astronomy Pic of the Day. There was recently a lunar eclipse. I missed it because I was in Florida where it rained for about 4 solid days without CEASING. But that’s another story.
In any event, in this very cool photo, you can see the shape of the Earth’s shadow.
Old Copernicus would have been thrilled. He was careful to observe eclipses, both solar and lunar, because the casting of the shadow meant that the light source was at 180°, directly opposite.
Speaking of Copernicus, I just finished fairly light book by Dava Sobel A More Perfect Heaven: How Copernicus Revolutionized the Cosmos. (UK edition HERE)
Traversing the shadow of the Earth, the Moon dimmed by degrees until fully immersed. Then, instead of disappearing in darkness, the eclipsed Moon daubed itself with the Sun’s color: It glowed like an ember throughout the hour of totality, reflecting all the dusk and dawn light that spilled into Earth’s shadow from the day before and the day ahead.
Copernicus never missed a lunar eclipse. No astronomer let such an opportunity slip, for the Moon in eclipse pinpointed celestial positions as no other phenomenon could. At such times the Earth’s shadow became visible on the Moon’s surface, and the center of that shadow indicated the location of the Sun—180° opposite in celestial longitude. With the Moon’s current coordinates thus confirmed, one could also measure the distances of stars and planets from either the Sun or the Moon. “In this area,” Copernicus remarked, “Nature’s kindliness has been attentive to human desires, inasmuch as the Moon’s place is determined more reliably through its eclipses than through the use of instruments, and without any suspicion of error.”
Even with the help of “Nature’s kindliness,” the tilt of the Moon’s orbit relative to the Earth’s great circle limited the frequency of lunar eclipses to once or at most twice a year, though some years have none. After August 26, there would not be another total lunar eclipse till the end of December 1525. At the moment of mid-eclipse, which Copernicus recorded on this occasion as 4:25 A.M., the Moon stood at opposition, yet stayed its course straight ahead. Unlike Jupiter or Saturn, the Moon never shifted into reverse at opposition—or ever, at any time—because the Moon, alone among all heavenly bodies, truly did orbit the Earth. “In expounding on the Moon’s motion,” Copernicus wrote, with no apparent irony, “I do not disagree with the ancients’ belief that it takes place around the Earth.”
Sobel, Dava (2011-10-04). A More Perfect Heaven: How Copernicus Revolutionized the Cosmos (Kindle Locations 702-718). Bloomsbury Publishing Plc. Kindle Edition.
Here is the quote from Sobel about Copernicus observing a lunar eclipse: