May 26th brings us a total eclipse of the moon

Photo: Public domain photo of lunar eclipse from April 15, 2014

Much of the country may be in for a wonderful celestial event. The May 2021 issue of Astronomy magazine describes the event in a feature article entitled “The Moon Turns Red.” In central Wisconsin, however, we are too far east to see all of it. But because a total lunar eclipse is an interesting thing to know about, I will mention some of the details. To start with, the moon must be full for a lunar eclipse, which it will be on the morning of May 26, 2021.

From 6:11 AM to 6:26 AM Central Daylight Time on that date (mark your calendar!) the moon will be completely in Earth’s total shadow (known as the “umbra,” Latin for “shadow.” During this time the moon is totally eclipsed. Prior to this, at 4:45 AM, the moon will have completely entered the Earth’s partial shadow, the “penumbra” (Latin for “next to the shadow”), and begins to enter the umbra. In the penumbra phase of a total eclipse, the moon simply turns very slightly darker. This is not noticeable as being different from the usual full moon without sensitive instruments.

In short, it seems to be the case that this eclipse will not be a particularly impressive show in central Wisconsin, in spite of the enthusiasm of moon watchers and the media. The main reason for this is that the Sun rises at 5:19 AM and the moon sets at 5:25 AM, at which time the moon will be about halfway into the umbra with a good-sized “bite” taken out of it. So if you have a good view of the eastern skies and the weather cooperates, you should be able to see the beginning of the disappearance of the moon into the umbra.

Even considering that the moon will have set over Wisconsin before full totality, I think it would be fun to imagine how this eclipse would appear if we could be on the surface of the moon, facing Earth, during a total lunar eclipse. Let us suppose that a company such as Space-X, far in the future, could offer round trips to the moon for about US$125,000 (economy class). During the penumbral phase, the Sun’s direct light would be seen off the edge of the Earth. Because direct viewing of that light would quickly damage or destroy the retinas of your eyes, you would need to protect them with a solar light filter, the same kind that you need to view the Sun or a solar eclipse from Earth.

But when the moon has entered the umbra —the complete shadow of the Earth — you would see that the Sun has disappeared from sight behind the Earth, with a pinkish-orange-yellow glow around the Earth. Those are the colors of sunset and sunrise. These colors would appear as a paper-thin layer around the Earth, because they are produced by the atmosphere of the Earth. The atmosphere of the Earth is roughly 10 miles (16 km) thick, the diameter of Earth is about 7926 mi (12, 742 km) and we would be looking at it from a distance of about 240,000 mi (384,000 km).

The softly colored glow we would see from the moon is the powerful sunlight refracted by Earth’s atmosphere, giving the moon its reddish-orange color during an eclipse, hence the name the “Blood Moon”. The intensity of the color is dependent on several factors, including the height of the moon above the horizon and the amount of dust in Earth’s atmosphere. The lower the moon in the sky and the greater amount of dust, the more intense the “blood” color.

If you have an intense interest in the May 26th total eclipse of the moon, you should plan to be in the western United States — the farther west the better. Happy viewing to you. I wish you clear skies; just enjoy the wonder of anything you see in a clear night sky. Praise to our Creator!