How Does a Lunar Eclipse Work: How Often Are Lunar Eclipses?

~6 min
How Does a Lunar Eclipse Work: How Often Are Lunar Eclipses?

A lunar eclipse is one of the most breathtaking astronomical events — our natural satellite gets engulfed by the Earth’s shadow and changes its color to red. Learn what types of lunar eclipses there are, why they occur, and when the next lunar eclipse happens.

Contents

What's a lunar eclipse?

A lunar eclipse occurs when the Earth fully or partially blocks the Sun’s light from reaching the Moon. This can only happen during the Full Moon phase. If the Earth, the Moon, and the Sun form a straight line, a total lunar eclipse occurs. If their alignment is not exact enough, observers will see a partial or penumbral lunar eclipse — or no eclipse at all.

Watch our short explanatory video to better understand how lunar eclipses work.

Types of lunar eclipses

There are three types of lunar eclipses: total, partial, and penumbral. Let’s take a closer look at each of them.

Total lunar eclipse

A total lunar eclipse is the most spectacular of the three types. It happens when the Sun, the Earth, and the Moon are precisely aligned in space. The Earth comes between the Moon and the Sun and covers the entire Moon with the inner part of its shadow, called the umbra. Interestingly, our natural satellite doesn’t completely disappear during a total eclipse but turns dark red. Why does it happen?

Although the Earth blocks all direct sunlight, a small portion of the light gets refracted by the Earth’s atmosphere and reaches the Moon’s surface. Our planet’s atmosphere scatters the blue-colored light but lets the red-colored light through. That’s why the lunar disk becomes red. Because of the distinctive reddish hue, a total lunar eclipse is often called a Blood Moon.

Partial lunar eclipse

A partial lunar eclipse occurs when only a part of the Moon gets covered by the Earth’s umbral shadow. This happens when the Sun, the Earth, and the Moon are not perfectly aligned. During this type of eclipse, only a portion of the Moon gets dark and reddish.

Penumbral lunar eclipse

A penumbral lunar eclipse occurs when the Moon passes through the penumbra — the outer part of the Earth’s shadow. It’s the least noticeable type of eclipse: for a keen-eyed observer, the Moon will look only slightly darker than usual.

Lunar eclipse vs solar eclipse

Both lunar and solar eclipses involve three celestial bodies: the Sun, the Earth, and the Moon. Here are the main differences between these two astronomical events.

  • During a lunar eclipse, which happens at night, the Moon gets covered by the Earth’s shadow.
  • During a solar eclipse, which happens in the daytime, the Sun gets covered by the Moon’s disk as seen from the Earth.
  • Lunar eclipses occur only at a Full Moon, while solar eclipses happen only at a New Moon.
  • A lunar eclipse can be observed from anywhere on the night side of the Earth. This is due to the fact that the Earth’s shadow is huge compared to the Moon.
  • Solar eclipses are visible only from specific locations where the Moon’s shadow falls. This is because the Moon’s shadow is much smaller than the Earth’s.

Interesting fact: eclipses always come in pairs. A solar eclipse occurs approximately two weeks before or after a lunar eclipse.

If you tend to confuse solar and lunar eclipses, remember this: when the Sun gets dark, we call it a solar eclipse, and when the Moon gets dark, we call it a lunar eclipse.

When is the next lunar eclipse?

The next lunar eclipse will occur on May 5, 2023. It will be a penumbral lunar eclipse. The eclipse will be visible from Eastern and Southern Europe, Asia, Africa, and Australia. The maximum phase of the eclipse will occur at 1:22 p.m. EDT (17:22 GMT).

When is the next total lunar eclipse?

The next total lunar eclipse will occur on March 14, 2025. It will be visible from the Americas, much of Europe, Asia, Australia, and Africa. The totality phase will begin at 2:26 a.m. EDT (06:26 GMT) and reach its maximum at 2:58 a.m. EDT (06:58 GMT).

If you want to learn about all lunar eclipses that will occur in the upcoming decade, use the eclipse calendar made by NASA. You can also check our infographic, where we list five future eclipses with their timelines and visibility maps.

List of 5 upcoming lunar and solar eclipses, their dates, timelines, and visibility maps. Find out whether you can see them from your location!
See Infographic

How often do lunar eclipses happen?

As we’ve already mentioned, a lunar eclipse always happens at a Full Moon. However, not every Full Moon comes with a lunar eclipse. Here’s why: the Moon’s orbit is tilted at about five degrees to the Earth’s orbit, so our natural satellite usually passes above or below the Earth’s shadow at a Full Moon. On average, two lunar eclipses occur every year. The maximum number of lunar eclipses in a year is five, though it happens quite rarely. The last time five lunar eclipses occurred in one calendar year was in 1879; the next time such an event will happen is in 2132.

How often do total lunar eclipses occur?

On average, a total lunar eclipse occurs every 2.5 years in any given location. Total lunar eclipses account for about 35% of all lunar eclipses.

How often do partial lunar eclipses occur?

According to NASA, at least two partial lunar eclipses occur every year. To get this number, NASA must have counted in partial phases of total lunar eclipses. If we consider partial lunar eclipses separately, they usually occur once a year or once every two years. About 30% of all lunar eclipses are partial.

How long does a lunar eclipse last?

Unlike solar eclipses, which last only a few minutes, lunar eclipses can last hours. That’s because the Earth’s shadow is quite large in relation to the Moon’s size. A total lunar eclipse can continue for up to two hours, and partial lunar eclipses can last even longer.

Longest lunar eclipse

The longest total lunar eclipse of the 21st century occurred on July 27, 2018. The totality phase lasted 102 minutes and 57 seconds. The next total lunar eclipse of a comparable length will occur only in 3107 and will last 106 minutes and 13 seconds.

Longest partial lunar eclipse

The longest partial lunar eclipse in nearly 600 years occurred on November 19, 2021. It lasted for 3 hours, 28 minutes, and 23 seconds. Before it, a partial eclipse of a similar length happened on February 18, 1440 (3 hours, 28 minutes, and 46 seconds). The partial lunar eclipse of November 2021 will remain the longest for another 648 years until the eclipse on February 8, 2669 (3 hours, 30 minutes, and 2 seconds).

How to see lunar eclipse?

You don’t need any special equipment to observe a lunar eclipse — though you can use binoculars to see more details on the red-shaded lunar surface. All you need to enjoy this astronomical event is a clear sky and an unobstructed horizon. To learn when the eclipse begins in your location, use the Eclipse Guide app.

F.A.Q.

Where can I see the lunar eclipse?

Lunar eclipses are visible from any place in the world where the Moon is above the horizon. In other words, you just need to be on the night side of the Earth at the time of the eclipse to see it. Check our infographic to learn where to see upcoming eclipses.

List of 5 upcoming lunar and solar eclipses, their dates, timelines, and visibility maps. Find out whether you can see them from your location!
See Infographic

Why isn't there a lunar eclipse every month?

Lunar eclipses don’t occur every month on a Full Moon because the orbits of the Moon and the Earth are not in the same plane. Most of the time, the Moon passes above or below the Earth’s shadow during a Full Moon. Watch our video to get a better understanding of why lunar eclipses don’t happen every month.

What does a red moon mean?

“Red Moon” and “Blood Moon” are simply alternative names for a total lunar eclipse. The eclipsed Moon looks red because sunlight gets refracted and scattered by the Earth’s atmosphere, with only red-colored light reaching the lunar surface. Read our article about the Blood Beaver Moon that occurs on November 8, 2022.

Is it safe to look at a lunar eclipse?

Unlike watching a solar eclipse (for which you need special solar filters), observing a lunar eclipse is absolutely safe for your eyes. That’s because the Moon doesn’t emit its own light but only reflects sunlight.

How to prove the Earth is round using a lunar eclipse?

At every lunar eclipse, the Earth’s shadow on the Moon is always circular and doesn’t change its shape with the planet’s rotation. The only shape that always makes a perfectly circular shadow is a sphere. Read our article to learn more ways to prove the Earth is round.

How does lunar eclipse affect humans?

You might hear that lunar eclipses can increase the risk of skin disease, badly affect pregnant women, or be harmful to digestion. However, there is no scientific evidence that lunar eclipses have any physical effect on people.

Bottom line: Now you know why lunar eclipses happen, what types they can be, and how they differ from solar eclipses. If you want to test your knowledge about eclipses, try our challenging quiz. We wish you clear skies and happy stargazing!

Complete the following quiz and see how much you really know about solar and lunar eclipses. By the end of it, you should gain a better understanding of these astronomical phenomena and learn some interesting historical facts that you probably didn't know. Decide whether the following statements are true or false.
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