What Is A Total Lunar Eclipse?

Solar vs Lunar Eclipses - What’s the Difference?

A solar eclipse happens at the new Moon when the Moon is between the Earth and the Sun. If you’re in the right place at the right time, you’ll see the Moon pass in front of the Sun. This is possible because the Moon is 400 times smaller than the Sun, but is also 400 times closer to us.

As a result, both the Sun and the Moon appear the same size in the sky and the Moon is able to completely obscure the Sun. As the Moon continues to move along its orbit, it casts a shadow onto the surface of the Earth and anyone standing in this shadow will see a total solar eclipse.

A lunar eclipse is almost the opposite of a solar eclipse. It can only occur at full Moon when the Moon is on the opposite side of the Earth from the Sun. This places the Earth directly between the Sun and the Moon.

The Earth, like the Moon during a solar eclipse, casts a shadow, and when the Moon passes through this shadow, we see a total lunar eclipse. Unlike a total solar eclipse, the darkened Moon is visible to anyone on the night side of the Earth, as long as the Moon is visible from that location.

If you’re wondering why solar and lunar eclipses don’t happen every month, it’s because the Moon’s orbit is inclined at an angle of 5.15 degrees. Most of the time, the Moon’s shadow will miss the Earth, or the Moon will pass above or below the Earth’s shadow, and there’ll be no solar or lunar eclipse.

Eclipses frequently come in pairs; you’ll find that when one eclipse occurs, another will follow just a few weeks later. For example, there was a new Moon and a partial solar eclipse on April 30th, 2022, then a full Moon and a total lunar eclipse on May 16th.

What are the Different Types of Lunar Eclipse?

There are three types of lunar eclipse, but before we review each one, we need to learn a little more about the Earth’s shadow. After all, it’s the Earth’s shadow that determines which type of eclipse will occur.

If you could clearly see the Earth’s shadow, it would look a little like a target. The “bullseye” at the center is the darkest part of the shadow and is known as the umbra. Surrounding this is the lighter part of the shadow, called the penumbra.

Now you know this, the three types of lunar eclipse are as follows: Penumbral, Partial, Total.

Penumbral or Partial - What’s the Difference?

As its name implies, a penumbral lunar eclipse occurs when the Moon only passes through the penumbra - the outer portion of the Earth’s shadow. As this is the lightest portion of the shadow, the Moon is only slightly dimmed. In fact, the chances are you might not notice anything different at all!

A partial lunar eclipse occurs when the Moon partially enters the umbra, the central and darkest portion of the Earth’s shadow. In this instance, you’ll see a portion of the Moon turn a coppery orange color, while the rest of its surface will appear regular pearly white. Every partial eclipse is a little different, depending upon how much of the Moon is eclipsed. Sometimes you’ll get an eclipse that’s nearly total - and might even look total to the naked eye - while other times the Moon will barely graze the umbra and you’ll barely notice anything at all.

However, the vast majority of the time, the Moon will be quite obviously partially eclipsed. How much of the surface will be in shadow is specified as a percentage. For example, the partial lunar eclipse of September 17th, 2024 will be nearly non-existent, with just 3.5% of the Moon in eclipse. Compare that to the partial lunar eclipse that occurs nearly two years later, on August 27th, 2026. In stark contrast, this eclipse is almost total, with 96.2% of the Moon in eclipse.

Image Credit: www.MrEclipse.com

Anatomy of a Total Lunar Eclipse

Lastly, a total lunar eclipse occurs when the entirety of the Moon’s surface is in shadow. The Moon passes completely through the central, umbra portion of the Earth’s shadow and we see the whole of the Moon turn a coppery color as a result.

The whole process, from start to finish, typically takes between four to six hours, with six distinct stages:

1. Penumbral Phase Begins
2. Partial Phase Begins
3. Totality Begins
4. Totality Ends
5. Partial Phase Ends
6. Penumbral Phase Ends

The penumbral and partial phases each last about an hour, with totality itself potentially lasting less than a minute to nearly two hours. The length (and to some extent, the intensity) of totality depends upon the Moon’s path through the umbra.

If the Moon skims through the outer portion of the umbra, then totality may only last a few minutes and the Moon might appear a light, coppery color. However, if the Moon passes directly through the center of the umbra, then totality could last nearly two hours and the Moon may appear a darker orange color.

When the penumbral phase begins, you might notice the Moon dimming slightly as it enters the Earth’s shadow, but you probably won’t notice any change at first. If you want to try and spot the difference, take a look at the Moon when it’s about midway through the penumbral phase.

(Don’t use an app or software to see which part of the Moon is already in the penumbra - see if you can detect the difference with just your eyes first!)

When the partial phase begins, you’ll see the leading edge of the Moon dim and start to darken. As the Moon slips into the umbra, more of its surface will darken and turn orange, providing a stark contrast to the portion of the lunar surface that remains in the penumbra.

During totality, you’ll notice that some parts of the Moon are darker than others, depending on which edge is closest to the center of the umbra and which is nearer the penumbra. The darkness and color of the eclipse can also vary, depending upon the Earth itself.

The reason the Moon doesn’t disappear completely is that the Earth’s atmosphere bends a little sunlight, which then dimly illuminates the lunar surface. Dust and pollutants in our atmosphere can block the light, causing the Moon to appear darker. For example, volcanic eruptions can have a significant effect on eclipses.

Some eclipses are so dark that the Moon disappears completely. After a series of volcanic eruptions early in the 12th century, the Moon was said to be unusually dark - to the point of invisibility - during the total lunar eclipse of May 5th, 1110 CE (see www.science.org for more information).

On the flip side, lunar eclipses can be so bright that it would seem as though the eclipse never happened at all. The total lunar eclipse of March 19th, 1848 started normally, but at around 8:40 PM observers in England were surprised to see the Moon prematurely return to its normal brightness.

According to one observer in Devon, “[..] the whole disk of the Moon being as perfect with light as if there had been no eclipse whatsoever” [sic].

(Mid-eclipse occurred at 8:12 PM, with totality ending a few minutes after 9 PM.)

The fact of the matter is that every eclipse is a unique and unmissable experience. It could be partial or total, bright or dark, and there could be bright stars and planets nearby. Regardless of the circumstances, a lunar eclipse is always worth venturing outside for!

Learn More

Interested in learning more about what's going on in the sky? Not sure where to begin? Check out our Astronomy Hub to learn more!

Astronomy Hub

This Article was Last Updated on 08/16/2023