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Lunar eclipses: Everything you need to know

Moon phases in the shape of a question mark. A blood red moon is caused by a lunar eclipse.
Moon phases arranged in the shape of a question mark. (Image credit: Kevin Lau Photography via Getty Images)

Lunar eclipses occur when Earth aligns between the sun and the moon and casts a shadow across the lunar surface. A lunar eclipse only happens during a full moon and can last as long as six hours, according to the European Space Agency (ESA). (opens in new tab) 

There are three types of lunar eclipses depending on how the sun, Earth and moon are aligned at the time of the eclipse.  

  1. Total lunar eclipse 
  2. Partial lunar eclipse 
  3. Penumbral lunar eclipse 

2022 will see two total lunar eclipses that will be visible in many parts of the world. The first lunar eclipse occurred on May 15-16 and the second will occur on Nov. 8. To find out when, where and how to see this year's lunar eclipses, check out our lunar eclipse 2022 guide

Related: How to photograph a lunar eclipse 

What are lunar eclipses?

A lunar eclipse is caused by Earth blocking sunlight from reaching the moon and causing a shadow across the lunar surface. The sun-blocking Earth casts two shadows that fall on the moon during a lunar eclipse: The umbra is a full, dark shadow, and the penumbra is a partial outer shadow.  

During a lunar eclipse the sun, Earth and moon align so that Earth blocks sunlight from reaching the moon and casts a shadow across the lunar surface. Whether the moon sits in the penumbra or umbra will dictate the type of lunar eclipse. During a total lunar eclipse, the umbra completely covers the lunar surface. In this diagram, the moon is located in the penumbral shadow so it is experiencing a penumbral eclipse. (Image credit: Future)
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According to TimeandDate.com (opens in new tab), a total lunar eclipse has seven stages:  

  1. Penumbral eclipse begins: This first stage is not that noticeable to the naked eye and occurs when the penumbral shadow begins to move across the moon. 
  2. Partial eclipse begins: The umbra begins to cover the moon. This is usually the first part of the eclipse visible to the naked eye.  
  3. Total eclipse begins: As the umbra completely covers the lunar surface, the moon turns a blood-red color. 
  4. Maximum eclipse: This is the stage of the eclipse with maximum coverage of the lunar surface by Earth's umbra.  
  5. Total eclipse ends: Earth's umbra begins to move away from the lunar surface as the eclipse begins to wrap up.  
  6. Partial eclipse ends: Earth's umbra leaves the lunar surface. 
  7. Penumbral eclipse ends: Earth's shadow is no longer cast across the lunar surface.  

During a partial lunar eclipse, only part of the moon enters Earth's shadow, which may look like it is taking a "bite" out of the lunar surface. Earth's shadow will appear dark on the side of the moon facing Earth. How much of a "bite" we see depends on how the sun, Earth and moon align, according to NASA (opens in new tab).  

Why is the moon red during an eclipse?

The moon turned blood-red over the Sossusvlei Desert Lodge on NamibRand Nature Reserve in Namibia in this stunning photo taken by skywatcher George Tucker on June 15, 2011. (Image credit: George Tucker)
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During a total lunar eclipse, the lunar surface turns a rusty red color, earning the nickname "blood moon". 

The eerie red appearance is caused by sunlight interacting with Earth's atmosphere

When sunlight reaches Earth, our atmosphere scatters and filters different wavelengths. Shorter wavelengths such as blue light are scattered outward, while longer wavelengths like red are bent — or refracted — into Earth's umbra, according to the Natural History Museum (opens in new tab). When the moon passes through Earth's umbra during a total lunar eclipse, the red light reflects off the lunar surface, giving the moon its blood-red appearance. 

"How gold, orange, or red the moon appears during a total lunar eclipse depends on how much dust, water, and other particles are in Earth's atmosphere" according to NASA scientists (opens in new tab). Other atmospheric factors such as temperature and humidity also affect the moon's appearance during a lunar eclipse. 

How often do lunar eclipses occur?

In astronomical terms, a lunar eclipse is a relatively common phenomenon, with about three lunar eclipses occurring every year, according to the National History Museum. Approximately 29% of lunar eclipses are total lunar eclipses, according to TimeandDate.com. 

Lunar eclipses are more easily observed than solar eclipses, as they can be viewed with the unaided eye by any observer situated where the moon is above the horizon. As such, a total eclipse can be seen from any given location — on average — once every 2.5 years. (Reminder: Never look directly at the sun, even during a total solar eclipse, without protection such as verified eclipse glasses; serious and permanent eye damage can result.)

How to watch a lunar eclipse

This montage of images taken by skywatcher Keith Burns shows the Dec. 20, 2010 total lunar eclipse. The photos won a NASA contest to become an official NASA/JPL wallpaper for the public. (Image credit: NASA/JPL-via Kieth Burns)
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Lunar eclipses are among the easiest skywatching events to observe. 

To watch one, you simply go out, look up and enjoy. You don't need a telescope or any other special equipment. However, binoculars or a small telescope will bring out details on the lunar surface — moonwatching is as interesting during an eclipse as it is at any other time. If the eclipse occurs during winter, bundle up if you plan to be out for the duration — an eclipse can take a couple of hours to unfold. Bring warm drinks and blankets or chairs for comfort.

TOP TELESCOPE PICK!

Celestron Astro Fi 102

(Image credit: Celestron)

Looking for a telescope for a lunar eclipse? We recommend the Celestron Astro Fi 102 (opens in new tab) as the top pick in our best beginner's telescope guide.  

Scientists like to watch lunar eclipses, too.

"We can get really good science out of what happens to the surface of the moon during total lunar eclipses, but again, the cool thing is that the moon changes color," Noah Petro, a research scientist at NASA's Goddard Space Flight Center in Maryland, told Space.com. "It's something fun to see — it's benign, but it's a change. And anytime we see [a] change in the skies, it's always kind of exciting."

If you hope to snap a photo of a lunar eclipse, here's our guide on how to photograph the moon with a camera. And if you need imaging equipment, our best cameras for astrophotography and best lenses for astrophotography have recommendations to make sure you're ready for the next eclipse.

The Earth blocks the sun during a total lunar eclipse, as seen from the moon. (Image credit: NASA)
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Additional resources

Learn more about lunar phases and eclipses with NASA Science (opens in new tab). Explore Hanwell Community Observatory (opens in new tab)'s fact sheet for more lunar eclipse information. Discover why we don't have a lunar eclipse every month with the Rice Space Institute (opens in new tab) at Rice University. 

Bibliography

NASA. Blood Red Moon: Total Lunar Eclipse. NASA. Retrieved May 10 (opens in new tab), 2022,

O'Callaghan, J. (2019, July 16). Lunar eclipse guide: What they are, when to see them and where. Natural History Museum (opens in new tab). Retrieved May 10, 2022. 

NASA. (2017, May 3 (opens in new tab)). What is an Eclipse? NASA. Retrieved May 10, 2022.

Hocken, V., Kher, A. Total Lunar Eclipse. timeanddate.com (opens in new tab). Retrieved May 10, 2022. 

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Daisy Dobrijevic
Reference Writer

Daisy Dobrijevic joined Space.com in February 2022 as a reference writer having previously worked for our sister publication All About Space magazine as a staff writer. Before joining us, Daisy completed an editorial internship with the BBC Sky at Night Magazine and worked at the National Space Centre in Leicester, U.K., where she enjoyed communicating space science to the public. In 2021, Daisy completed a PhD in plant physiology and also holds a Master's in Environmental Science, she is currently based in Nottingham, U.K.

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