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What is a blood moon?

A blood moon taken on 27 July 2018
(Image credit: ESA/CESAR–M.Castillo)

A "blood moon" happens when Earth's moon is in a total lunar eclipse. While it has no special astronomical significance, the view in the sky is striking as the usually whiteish moon becomes red or ruddy-brown.

The moon orbits around Earth, while Earth orbits around the sun. The moon takes about 27 days to orbit Earth and goes through regular phases in a 29.5-day cycle. The difference in these two cycles has to do with the relative positions of the sun, Earth and moon, which change during the moon's orbit.

Lunar eclipses can only happen during a full moon, when the sun fully illuminates the surface. Usually a full moon has no eclipse because the moon orbits in a slightly different plane than the Earth and the sun do. However, at times the planes coincide. Earth passes in between the moon and the sun and cuts off the sunlight, causing an eclipse.

If Earth partially blocks the sun, and the darkest part of its shadow falls across the moon's surface, it is called a partial eclipse. You will see a black shadow taking a bite out of the moon. Sometimes, the moon passes through the lighter part of Earth's shadow, causing a penumbral eclipse. Only seasoned skywatchers will be able to tell the difference, because the moon only darkens very slightly.

During a full eclipse, however, something spectacular happens. The moon is fully in Earth's shadow. At the same time, a little bit of light from Earth's sunrises and sunsets (on the disk of the planet) falls on the surface of the moon. Because the light waves are stretched out, they look red. When this red light strikes the moon's surface, it also appears red. 

Skywatcher Keith Burns took this montage of images, which shows the Dec. 20, 2010, total lunar eclipse. The montage won a NASA contest to become an official NASA/JPL wallpaper for the public. (Image credit: Keith Burns/NASA/JPL)

How red the moon appears can depend on how much pollution, cloud cover or debris there is in the atmosphere. For example, if an eclipse takes place shortly after a volcanic eruption, the particles in the atmosphere will make the moon look darker than usual.

While there are planets and moons all over the solar system, only Earth is lucky enough to experience lunar eclipses because its shadow is just large enough to cover the moon completely. The moon is slowly drifting away from our planet (at roughly 1.6 inches or 4 centimeters a year) and this situation won't persist forever. There are roughly two to four lunar eclipses every year, according to NASA, and each one is visible over about half the Earth.

How a blood moon saved Christopher Columbus

Some ancient cultures didn't understand why the moon turned red, causing fear. At least one explorer — Christopher Columbus — used this to his advantage in 1504. 

According to a jlaye.com Skywatching columnist Joe Rao, Columbus and his crew were stranded on an island now known as Jamaica. At first the Arawak people who lived there were welcoming, but over time, Columbus' crew grew restless and murdered or robbed some of the natives. Understandably, the native people weren't eager to help the crew search for food, and Columbus realized famine was drawing near. 

A photograph of a blood moon taken in 2018

A blood moon seen over California in 2018. (Image credit: Getty Images )

Columbus had an almanac with him foretelling when the next lunar eclipse would take place. Armed with this information, he told the Arawak that the Christian god was unhappy that Columbus and his crew received no food. God would turn the moon red as a symbol of his anger, Columbus said. As the event took place, frightened people "with great howling and lamentation came running from every direction to the ships laden with provisions, praying to the Admiral to intercede with his god on their behalf," according to an account by Columbus' son Ferdinand.

When is the next blood moon?

The next total lunar eclipse, and therefore the next blood moon, will be May 16, 2022. Several partial and penumbral lunar eclipses occurred since the previous total lunar eclipse on May. 25-26, 2021, and NASA has .

Additional resources

If you have a budding astronomer at home who wants to learn more about eclipses check out by Ruth Owen or take a look at NASA's Space Place on the different types of moons.

Bibliography

K. G. Strassmeier et al "High-resolution spectroscopy and spectropolarimetry of the total lunar eclipse January 2019," Astronomy & Astrophysics, Volume 653, March 2020,

Natural History Museum, "," May 27, 2021. 

Royal Museums Greenwich, "," January, 2022. 

Jessica Marshallsay, "," The University of Queensland, January, 2022.

to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community@jlaye.com.

Elizabeth Howell

Elizabeth Howell, Ph.D., is a contributing writer for since 2012. As a proud Trekkie and Canadian, she tackles topics like spaceflight, diversity, science fiction, astronomy and gaming to help others explore the universe. Elizabeth's on-site reporting includes two human spaceflight launches from Kazakhstan, and embedded reporting from a simulated Mars mission in Utah. She holds a Ph.D. and . in Space Studies from the University of North Dakota, and a Bachelor of Journalism from Canada's Carleton University. Her latest book, NASA Leadership Moments, is co-written with astronaut Dave Williams. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday.

Sự thật chơi số đề online 1 ăn 99? Tại sao tỷ lệ ăn cao như vậy

Sự thật chơi số đề online 1 ăn 99? Tại sao tỷ lệ ăn cao như vậy