Two lunar eclipses await astronomy enthusiasts in 2021.
The first is a total lunar eclipse during which the Sun, the Moon and the Earth are perfectly aligned, and the Moon enters the darkest part of the Earth’s shadow, the umbra.
The second one, near the end of the year, is a partial lunar eclipse when the three celestial bodies are imperfectly aligned such that the Moon enters Earth’s outer shadow, the umbra.
This post will guide you through why and how a lunar eclipse occurs, which kinds of lunar eclipses are out there, and what you can expect for 2021.
Discover the solar eclipses of 2021
What is a Lunar Eclipse?
Eclipses occur when the Moon’s orbit places it between Earth and the Sun, an alignment called syzygy (pronounced SIZ-eh-gee). At times, the Moon passes through Earth’s shadow, i.e. the Earth falls directly between the moon and the sun.
Since our planet blocks sunlight from landing on the moon, it causes a lunar eclipse. The only light coming from the moon during an eclipse is sunlight that passes through Earth’s atmosphere, hits the Moon’s surface and reflects back towards Earth.
This is why the Moon is much darker during an eclipse, and why it can appear red, as you’ll see in the ‘Blood Moon’ section, further down the page.
Lunar eclipses are visible from a much larger part of the globe than a solar eclipse. This is because Earth creates the shadow (the Moon creates the shadow which causes a solar eclipse) and its shadow is larger than the Moon. The Moon stays in the shadow for a long time, allowing more of Earth’s surface to witness the eclipse.
What Are the Different Types of Lunar Eclipses, and How Often Do They Occur?
There are three types of lunar eclipses: total, penumbral, and partial. The time period between two lunar eclipses can be 1, 5 or 6 synodic months.
A lunar eclipse only occurs when the moon is full, which is logical because the Sun needs to be behind the Earth, opposite the Moon, to cast a shadow on its surface. The Moon is full whenever the Sun is opposite it.
However, not every full moon results in an eclipse because the orbital plane of the Moon varies by about 5° from Earth’s. Sometimes the Moon is above Earth’s shadow and, other times, below it.
Astronomers recognize two kinds of shadows: the outer penumbra, where the Earth blocks only part of the Sun’s rays from reaching the moon, and the umbra, where the Earth shields the moon from all of the Sun’s rays.
Think of it from the perspective of standing on the lunar surface. If you are in the penumbra, the Earth blocks only some of the Sun from view. In the Umbra, our planet would stop you seeing any part of the Sun.
Depending on where the moon is in relation to these two types of shadow, three types of lunar eclipses can occur.
Penumbral Lunar Eclipse
This occurs when the Moon, Earth and the Sun are imperfectly aligned such that the moon is only in Earth’s penumbra, and does not touch the darker umbra.
These eclipses are hard to observe because the lunar surface is not drastically darkened unless it travels very near to the umbra.
Partial Lunar Eclipse
In a partial lunar eclipse, the Moon is at least partly covered by Earth’s umbral shadow.
The umbral shadow is much darker on the lunar surface, which is easy to observe with the naked eye.
There are five partial lunar eclipses due in the 2020s. One of them is in November this year, the rest can be found in the table at the bottom of the page.
Total Lunar Eclipse
When all three celestial bodies are perfectly or near-perfectly aligned, the Moon moves completely into Earth’s umbra. No sunlight can make it directly to the lunar surface, causing a total lunar eclipse.
The entirety of the Moon passes through Earth’s shadow, casting it in complete darkness. Some sunlight, especially the red part, is scattered by Earth’s atmosphere and falls onto the moon, giving it a dim, often reddish, glow.
Total lunar eclipses make up 35% of all lunar eclipses each year, and are seen from any location on Earth approximately every 2.5 years.
What Causes a Blood Moon During An Eclipse?
A blood moon occurs during a total lunar eclipse, when the moon is completely snuggled inside Earth’s umbral shadow.
Sunlight passing through Earth’s atmosphere scatters through a process called Rayleigh scattering (similar to how the Sun is red during sunsets and sunrises). Red wavelengths are not scattered as much, and pass right through Earth’s atmosphere and land on the moon.
The moon then reflects this red color, which we see from Earth. This phenomenon is called a Blood Moon. Although widely used, Blood Moon is not a scientific term.
How to See a Lunar Eclipse
The good news is that you don’t need any special equipment to observe a lunar eclipse. So long as the full moon is visible from you location on eclipse night, you’ll be able to see it with the naked eye.
You can, of course, use binoculars or a beginner’s telescope (link opens our favorite choices in a new tab) to heighten your enjoyment of the experience. These will let you more closely track the progress of Earth’s shadow as it passes over the lunar landscape.
At their most extreme, Lunar eclipses can last almost four hours, with totality itself lasting more than 100 minutes.
How Often Do We See an Eclipse of the Moon?
Lunar eclipses are much more frequent than those of the Sun. There are approximately five lunar eclipses every two years somewhere on the Earth’s surface.
Any particular location can expect to see some kind of lunar eclipse at least annually because the Earth’s shadow, by definition, covers half the planet.
It is possible to have as many as five eclipses in a calendar year, but this is a rarity, happening just 35 times in a 5000 year period; the next one is in 2132.
Most years (71%) have two eclipses in them, if we include all types of eclipse. If we only look at total lunar eclipses, the maximum number that can occur in one year is three. The last time this happened was 1982, and the next is due in 2485.
Lunar Eclipses 2021
Two lunar eclipses await astronomers in 2021. The first is a total lunar eclipse, and the second is a partial eclipse. Let’s see what each of them are, and where you’ll need to be to watch them
Total Lunar Eclipse | May 26, 2021
Eclipse Visibility: Southeast Asia, Australia, Canada, United States.
The first lunar eclipse of 2021 will be a total one lasting just over five hours from 8:48 UT to 13:50 UT on May 26, 2021.
The period of totality is just 14 minutes, making this a very shallow total eclipse of the Moon.
- The Moon enters Earth’s penumbra: 08:48 UT
- Partial eclipse begins (Moon enters Earth’s Umbra): 09:45 UT
- Total eclipse begins: 11:12 UT
- Eclipse midpoint: 11:19 UT
- Total eclipse ends: 11:26 UT
- Partial eclipse ends: 12:52 UT
- Moon leaves penumbra: 13:50 UT
Partial Lunar Eclipse | November 19, 2021
Eclipse Visibility: North and South America, Eastern Asia, Northern Europe.
The second lunar eclipse of 2021 is a partial one lasting six hours from 06:03 UT to 12:04 UT on November 19, 2021.
At the time of the greatest eclipse, 97% of the moon will be in Earth’s shadow, which is about as close to a total eclipse as it’s possible to be without actually being one.
- The Moon enters Earth’s penumbra: 06:03 UT
- Partial eclipse begins (Moon enters Earth’s Umbra): 07:20 UT
- Greatest eclipse: 09:04 UT
- Partial eclipse ends: 10:48 UT
- Moon leaves penumbra: 12:04 UT
Future Lunar Eclipses
This table shows all the lunar eclipses we expect to see to the end of the decade. We will, of course, bring full details of each nearer the time.
|26 May 2021||Most of Australia, southeast Asia, most of North and South America||Total|
|18-19 Nov 2021||Eastern Asia, North and South America, UK, western Europe and Africa||Partial|
|15-16 May 2022||Most of North and South America, western Europe, and most of Africa||Total|
|8 Nov 2022||Most of Asia and Australia, most of North and South America, eastern Europe||Total|
|5-6 May 2023||Most of Europe, Africa, Asia, and Australia||Penumbral|
|28-29 Oct 2023||All of Europe, Africa, Asia, and Australia. East of North and South America||Partial|
|24-25 May 2024||North and South America, UK, far western Europe and Africa, eastern Asia and Australia||Penumbral|
|17-18 Sept 2024||Most of North and South America, all of Africa, most of Europe, western Asia||Partial|
|13-14 Mar 2025||Eastern Asia and Australia, all of North and South America, western Europe and Africa||Total|
|7-8 Sep 2025||All of Europe, Africa, Asia, and Australia, western North America, eastern South America||Total|
|3 Mar 2026||East Asia, Australia, North and South America||Total|
|27-28 Aug 2026||Most of North and South America, most of Europe, all of Africa, western Asia||Partial|
|20-21 Feb 2027||Most landmasses, except western USA and Canada, and western Australia||Penumbral|
|16-17 Aug 2027||North and South America, western Africa, eastern Australia and Asia||Penumbral|
|11-12 Jan 2028||All of North and South America, all of Africa, most of Europe||Partial|
|31 Dec 2028||Eastern Africa, most of Europe, all of Asia and Australia, western North America||Total|
|26 Jun 2029||North and South America, western Europe and Africa||Total|
|20 Dec 2029||North and South America, all of Europe and Africa, most of Asia||Total|
|9-10 Dec 2030||Most landmasses except eastern Australia||Penumbral|
Lunar eclipses give you a chance to watch the solar system at work right in front of your eyes; of the Moon around Earth and Earth around the sun.
What’s more, they are so easily viewed that they make a compelling introduction to astronomy for stargazers of all ages.