During a total eclipse of the Moon, it's not uncommon to see the Moon's face shine with a dull, rusty-colored light. This is the result of red sunlight, filtered through the Earth's atmosphere, and shining on the Moon's surface. If you could be on the Moon during a total eclipse, the Earth would appear as a dark circle blocking the Sun, surrounded by the bright red-orange ring of the Earth's atmosphere.
Often, this rusty color can be a deep red, not unlike the color of blood. For this reason, every time we have a lunar eclipse, there are always some who proclaim it as "a sign of the End Times." Scripture mentions similar occurrences in the Moon:
" The Sun shall be turned into darkness, and the Moon into blood, before that great and notable day of the Lord come." -- Joel 2:31, Acts 2:20
"And I beheld when he had opened the sixth seal, and lo, there was a great earthquake, and the Sun became black as sackcloth of hair, and the Moon became as blood." -- Revelation 6:12
However, I would caution everyone against interpreting these passages to mean a simple lunar eclipse. The fact is, lunar eclipses are very common, moreso even than "wars and rumors of wars." There are usually two or three lunar eclipses each year. So a typical eclipse of the Moon is not a very rare or notable event in the scheme of human history.
Also, the causes and mechanics of eclipses were well understood in New Testament times. We've speculated in previous Updates that the education of the Apostle Paul might have included Classical Astronomy. So it's not unlikely that Paul and other Christians in New Testament times would have understood that a lunar eclipse is a predictable natural event, not a supernatural one.
Instead, perhaps the bloody color of the Moon foretold in Scripture refers to a supernatural event. These verses also speak of a darkening of the Sun. This only happens naturally during a total eclipse of the Sun. But a solar eclipse cannot happen at the same time as a lunar eclipse, since these events both involve the Moon, and can only occur at least two weeks apart, when the Moon is in opposite sides of the sky.
Also, a solar or lunar eclipse can only be seen in small areas of the Earth. No single eclipse is visible from everywhere in the world. Also, eclipses are short in duration. Solar eclipses last only a few minutes, while lunar eclipses last for less than two hours. Surely events signaling the climax of human history should be longer in duration, and visible to everyone in the world, so that every eye could see the fulfillment of prophecy.
For these reasons, I believe the opening of the Sixth Seal points to a non-astronomical event, where the Sun is darkened at the same time as the Moon turns to the color of blood. The Bible speaks of other miracles of the sky, such as the Star of Bethlehem and the darkness that occurred during the Crucifixion of Jesus. But these miracles are also not easily explained by astronomical science.
Many scientific theories have been proposed for the Star of Bethlehem. But there are a million of these theories, and they always seem to neglect either a point of Scripture or a point of science. And it has often been suggested that darkness on Calvary was due to a solar eclipse. But this darkness lasted for three hours, much longer than any natural eclipse. And the Crucifixion occurred during Passover, which lands on the Full Moon, the opposite phase for a solar eclipse!
Attempts to discover scientific rationalizations for the miraculous always require a "faith" in naturalistic explanations that advance neither science nor faith. We Christians might do better to simply trust what God wrote in His Word and not make hasty efforts to harmonize Scripture with human reason.