The Effects of Lunar Eclipses

By Steve LaNore; Updated April 24, 2017
The moon entering the umbra shadow during a lunar eclipse.

A lunar eclipse happens when the moon passes into a large shadow on the side of the Earth facing away from the sun. The sun, moon and Earth must line up within a very narrow range of angles for a lunar eclipse, so this event doesn't happen every time the moon passes behind the Earth. Lunar eclipses create effects you can see, along with invisible ones.

Penumbra Shadow

The moon first enters the outer partial shadow called the penumbra. The moon's brightness gradually fades and appears to have a dimmer portion, which moves from left to right across the moon face as it travels deeper into the penumbra.

Umbra Shadow

When the moon moves into the umbra — the darkest portion of the Earth’s shadow — it begins to appear as though a bite has been taken out of the moon. This "bite" grows until the moon is completely within the total eclipse phase. It becomes fully visible as a copper orange-red color once it's all the way inside the umbra shadow.The color comes from sunlight bent through the Earth’s atmosphere and reaching the moon before being reflected back to Earth. Visual results may vary depending on the clarity of the sky and amount of light around the observation point.

Eclipse Duration

The process reverses as the moon leaves the shadow. A lunar eclipse lasts a total of about three hours from start to finish. The period of “totality” — when the moon is in the umbra — usually lasts about an hour, with some variation for each eclipse.

Moon Tidal Forces

The pull of the sun and moon add to the tidal effects anytime they're in line with the Earth. They subtract from the tidal pull when the sun and moon are at right angles to each other from Earth. Because a lunar eclipse only takes place during a full moon, tides are higher during this time.

Wildife and Eclipses

Centuries-old lore claims that wildlife behave differently during a lunar eclipse. A study of the owl monkey conducted in 2010 by the University of Pennsylvania Department of Anthropology showed a pronounced change in monkey activity during a lunar eclipse. The study suggests this is due to the changing light levels as the eclipse proceeds.

People and Eclipses

A lunar eclipse only occurs during a full moon, so there's a widely held belief that such an eclipse affects people. However, science can find no such link that full moons and lunar eclipses have a measurable effect on humans.

About the Author

Steve LaNore has written and produced broadcast reports/specials and printed literature since 1985 and been a Web writer since 2000. His science blogs/reports can be seen on the Web site of KXII-TV. LaNore is a five-time award-winning meteorologist and member of the American Meterological Society as well as a Certified Broadcast Meteorologist sealholder. He holds a Bachelor of Science in meteorology from Texas A&M University.