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July 27, 2018

Are You Ready for July’s Total Lunar Eclipse?

Fortunate sky watchers in many parts of the world will witness a rare “Blood Moon” during an unusually long total lunar eclipse occurring on the evening of July 27 and into the early morning hours of July 28. A lunar eclipse occurs when the Earth is positioned between the sun and the moon. The moon darkens as it passes through the Earth’s shadow. The lunar eclipse will be visible in South America, East Africa, the Middle East and central Asia. Unfortunately, North America and most of the Pacific Islands will miss the sky show completely.

What is a total lunar eclipse?

A total eclipse occurs if the entire moon passes through Earth’s shadow. For a brief time, the moon will be completely obscured by Earth’s shadow. It will look as if the moon has disappeared from the night sky. A partial eclipse occurs if only part of the moon passes through the shadow.

Why will this eclipse last longer than others?

The total lunar eclipse that will occur this month is expected to be one of the longest to occur this century. From start to finish the moon will spend nearly 4 hours (3 hours and 55 minutes) crossing within Earth’s shadow. The phase of the eclipse where the moon is completely covered by Earth’s shadow—called the totality—will last 1 hour 42 minutes and 57 seconds. Compare that to the shortest lunar eclipse that occurred this century. On April 4, 2015, it lasted only 4 minutes and 48 seconds.

This year’s lunar eclipse is especially long-lasting because the moon will pass through the central part of the Earth’s shadow. In addition, the full moon will also be at the lunar apogee—the point when the moon is at its most distant point from Earth. The moon appears smaller in the sky and since it is farther away, it takes more time to cross the Earth’s shadow than does a full moon that’s closer to Earth. That’s why a full moon at or near lunar apogee leads to a longer lunar eclipse. The longest duration possible for a total lunar eclipse is 1 hour 47 minutes.

What is a “Blood Moon”?

During much of this month’s lunar eclipse, the moon will appear in the sky with a deep red hue, often called a “Blood Moon.” This will be the longest Blood Moon this century!

The moon does not become completely dark during most lunar eclipses. In many cases, it becomes reddish. Earth’s atmosphere bends part of the sun’s light around Earth and toward the moon. This light is red because the atmosphere scatters the other colors present in sunlight in greater amounts than it does red.

Don’t forget to look at Mars!

During the total lunar eclipse this month, sky watchers will be treated to an extra bonus—Mars will be in opposition on the same night! Mars and Earth both orbit the sun, but at different distances, and thus, different speeds. Every few years, Mars, Earth and the sun form a straight line during the course of their orbits, with Earth in the middle—an event known as opposition.

In the very dark sky that occurs when the moon is eclipsed, Mars can be seen easily with the naked eye. In fact, Mars will be especially bright because it is near its closest approach to Earth in the course of its orbit around the sun. For people watching the sky from Earth, Mars will appear about five times brighter than it does in other months.

Learn more fascinating facts about the Earth and Earth’s Moon in World Book’s Explore the Solar System series of books!

Image Credit: © Meowu/Shutterstock

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