On January 20, observers across North America see a total lunar eclipse. Unlike a total solar eclipse that is only visible for a few minutes from a narrow strip of ground, a lunar eclipse is visible everywhere the moon is above the horizon. That’s from half the planet. Another difference is that the light of a lunar eclipse is safe to view.
A lunar eclipse occurs when the moon is near its full phase and it moves through our planet’s shadow. The entire eclipse occurs over several hours. The best part of this eclipse occurs for about an hour. So if there’s cloudy weather, the eclipsed moon might be visible through a break in the clouds.
Our planet’s shadow is composed of a dark inner core where the moon is totally eclipsed. This is called the umbra. Ringing the umbra is a shadow where sunlight still somewhat shines. When the moon is in this penumbra, the moon dims only slightly. Without special equipment to measure the moon’s brightness, most of us will not likely see much change.
The eclipse begins on the evening of January 20 and concludes early the next morning. Here are the events of the eclipse as seen from Chicago:
- Jan. 20, 8:35 p.m. CST: The nearly full moon begins to move into the penumbra. The lunar sphere is about halfway up in the eastern sky. There’s not much change when the moon is in this part of the shadow.
- 9:33 p.m.: The moon continues to climb into the eastern sky. The moon begins to move into the umbra. During the next several minutes, the lower left portion of the moon begins to darken as the moon moves into the umbra. This partial eclipse continues for over an hour as the moon moves farther into the shadow. Interestingly, the moon appears to be moving higher in the sky as the eclipse progresses from Earth’s rotation. The moon is slowly revolving eastward into our shadow.
- 10:40 p.m. – 11:43 p.m. CST: The moon is high in southeast when totality begins. It is totally immersed in the earth’s shadow, appearing as the image shows at the top of of this article. The moon appears a deep ruddy orange color. Depending on the amount of dust in the atmosphere, the moon could be dimly illuminated, nearly disappearing. The orange color is from some of the sun’s light streaming through Earth’s thin atmosphere into the shadow. Without the atmosphere, the moon would be completely dark. In today’s popular press, this is known as a “blood moon.” This is the time to see eclipse. The moon is high in the south when totality ends.
- 11:12 p.m. CST: The moon is midway through the total eclipse. The moon is near its perigee — closest point to earth. This distance qualifies it as a “super moon” if the moon where full. So this eclipse will be known popularly as a “super blood moon” or a “blood super moon.” This is a total lunar eclipse, an elegant name without the popular descriptions.
- Jan. 21, 12:51 a.m. CST, The moon, high in the south-southwest exits the umbra. It is partially eclipsed.
- 1:49 a.m. CST, The eclipse is finished with the moon high in the southwest.
The next lunar eclipse visible from mid-America is on July 5, 2020 when the moon only passes through Earth’s penumbra. Another similar penumbral eclipse occurs on November 30, 2020. Chicago sees part of a total eclipse on the morning of May 26, 2021, but the moon sets before totality sets in.