How and Why Do Lunar Eclipses Occur?

Have you ever seen a red moon in the sky? The Moon turns complete red on a full moon night during a lunar eclipse. But a full moon occurs every 29 days, so why don’t you see a red moon every full moon, and why does the lunar eclipse even occur?

Why Do Lunar Eclipses Occur?

There are a couple of space facts that you need to be aware of to better understand why exactly a lunar eclipse occurs.

1. The Earth revolves around the Sun, and the Moon revolves around the Earth.
2. The Moon’s orbit is approximately 5° tilted relative to the Earth’s orbit around the Sun.

Because the Earth orbits the Sun and the Moon orbits the Earth, there are times when either the Moon or the Earth comes in the way of the light that’s coming from the Sun. When all three celestial bodies align in nearly a perfect row, with the Earth positioned between the Sun and the Moon, a lunar eclipse occurs. During a lunar eclipse, the Moon is unable to receive sunlight, causing the Earth’s shadow to be cast onto the Moon.

A lunar eclipse only occurs during a full moon night, but not on every full moon night. The reason behind this is that the Moon’s orbit around the Earth is tilted by 5.15° relative to the Earth’s orbit around the Sun. Because of this, it only rarely happens that all three bodies form a nice line. If the moon weren’t offset slightly, a lunar eclipse would occur every full moon day (an interval of about 29 days).

Now that you understand why a lunar eclipse occurs, it’s time to check out the different types of lunar eclipses—total lunar eclipse, partial lunar eclipse, and penumbral eclipse. To understand the difference between each of these lunar eclipses, there are, again, a few things that you need to be aware of.

During a lunar eclipse, the Earth casts two different shadows on the Moon. The first and bigger shadow is known as the penumbra, and it fans outward behind the Earth. The other shadow is called the umbra, and it is cast just behind the Earth. This shadow is comparatively narrower and darker than the penumbra.

Total Lunar Eclipse

A total lunar eclipse is when you see a red or blood moon. This event occurs when the Moon enters the umbra shadow area—just behind the Earth. Unlike shorter-wavelength colors, longer-wavelength colors like red and orange don’t scatter as much when they hit the Earth. Instead, they refract inward and continue toward the Moon. As a result, during a lunar eclipse, the Moon appears orangish or reddish in color.

Partial Lunar Eclipse

Unlike in a total lunar eclipse, where all three bodies are in perfect (mostly) alignment, a partial lunar eclipse occurs when they are not perfectly aligned. In this eclipse, only a portion of the Moon reaches the umbra shadow area. Since the umbra shadow area is very dark, the part of the Moon that passes to the umbra area sees a very dark Earth shadow form on it.

Penumbral Eclipse

You’ll see the penumbral lunar eclipse when the Moon passes through the penumbral shadow area. Since the Earth’s shadow that forms on the Moon in the penumbral area is very dim, there’s a high possibility that you’ll not even notice a penumbral lunar eclipse. During this eclipse, the Moon will appear just slightly darker than on normal days.

How Can You View a Lunar Eclipse

Fortunately, NASA doesn’t recommend any safety measures for viewing a lunar eclipse. During this event, the Moon doesn’t get any brighter than a regular full moon, meaning it has roughly the same brightness as on any other night. As a result, you can safely watch a lunar eclipse with the naked eye.

However, if you want to enhance your view, you can consider using binoculars, a telescope, or another optical device of your choice. Additionally, you’ll get the best view of a lunar eclipse if the sky is clear and your line of sight isn’t blocked by tall skyscrapers.

In contrast to a lunar eclipse, you must use eclipse glasses that comply with the ISO 12312-2 international safety standards to watch a solar eclipse. Even while wearing eclipse glasses, you should make sure that you’re not looking at the solar eclipse through a camera lens or binoculars, as the concentrated solar rays coming during the eclipse can come through your device’s lens and damage your eyesight. In some cases, your smartphone or any other device that you’re using to view the eclipse may also get damaged.

Now that you have a brief understanding of the lunar eclipse, check out the dates of some upcoming lunar eclipses so you don’t miss the next one.

That’s all you need to know about the lunar eclipse! It’s an incredible astronomical phenomenon that you should try to witness whenever it happens. As mentioned earlier, there are two lunar eclipses in both 2025 and 2026, so be sure to head up to your rooftop and watch this cosmic event unfold.