Five Fast Facts About Lunar Eclipses

The night sky is awe-inspiring, even more so when something out of the ordinary, like a lunar eclipse, happens.

(Photo via Shutterstock)

Total lunar eclipses occur at least twice a year, but they aren’t visible from everywhere on Earth. This year, we will experience lunar eclipses on May 15 and Nov. 8. The May 15 eclipse will be fully visible in Will County, but we won’t be so lucky in November. While we should get a partial glimpse of the November eclipse, we aren’t in the path of totality, where the full eclipse will be visible.

Lunar eclipses happen only during a full moon. They occur when Earth is directly between the sun and the moon. When this happens, Earth casts its shadow on the moon. During the period of totality, when Earth is directly between the sun and the moon, the moon has a red hue, which is why we call lunar eclipses blood moons.

Read on to learn more about lunar eclipses.

There are three different kinds

Not all lunar eclipses are created equal. There are three different types of eclipses — total, partial and penumbral — and they all appear different in the night sky. A total lunar eclipse is the real showstopper. This is when the moon, Earth and sun are perfectly aligned and Earth casts a shadow on the entire visible surface of the moon.


Words to know

Aligned: To place or arrange things in a line.

Atmosphere: The gases surrounding Earth or another planet.

Lunar: Related to the moon.

Omen: An event regarded as good or evil.

Penumbra: The shaded outer region of a shadow cast by an object.


During a partial lunar eclipse, Earth and the moon don’t line up perfectly. The Earth will still cast a shadow on the moon, but the shadow won’t cover the moon’s entire visible surface. Instead it looks like there is bite taken out of the moon. Total lunar eclipses include partial eclipses both before and after the eclipse reaches totality, so you can view this bite out of the moon during a total lunar eclipse as well.

A penumbral eclipse occurs when the moon passes through Earth’s penumbra, which is the outer part of its shadow. When this happens, the moon will appear more dim than usual. These eclipses aren’t much to look at. You probably wouldn’t even notice it is happening.

They give the moon an eerie hue

Lunar eclipses aren’t called blood moons for nothing. A lunar eclipse makes the moon red in the night sky because of how light from the sun passes through Earth’s atmosphere. It’s only during the totality of the eclipse that the moon looks red, and it’s for the same reason the sky looks blue.

It’s because of a principle called Rayleigh scattering. Sunlight moves in waves, and the different colors of light — red, orange, yellow, green, blue, indigo and violet — have different properties. When red light travels through the atmosphere, it bends, or refracts, on each side of Earth. This allows the red light to be cast on the moon during an eclipse.

A lunar eclipse will not always appear the same shade of red because it depends on the current conditions in Earth’s atmosphere. More clouds or dust in the atmosphere will make the moon look more red, while a cleaner atmosphere will make it look less red.

They used to induce fear

Our understanding of the solar system is much greater today than it was in previous generations, so now we know an eclipse is going to occur long before it does. Centuries ago, though, lunar eclipses weren’t well understood, and they were a cause for concern. People didn’t understand why eclipses occur, so seeing the moon turn blood red in the night sky was frightening. Many believed that a god was using the eclipse as a sign.

As frightening as a lunar eclipse may have been, solar eclipses were even more so. The blotting out of the sun in the middle of the day was thought to be a bad omen and a trigger for tragic events. In the 1600s, people in England believed a solar eclipse may have triggered the Great Plague of London. Centuries earlier, in 585, a war was ended because the two sides believed a solar eclipse was a godly sign that their actions were wrong.

They're predictable today

Since we understand why and how lunar eclipses occur, we no longer fear them. We even know when they will occur months, years, even decades ahead of time. You can look up when a lunar eclipse will occur in 2049 on the NASA Eclipse Website; you can even find out when eclipses occurred in 1901 if you want.

Even though we know when they will occur, they don’t always occur at the same time. And we don’t always have the same number each year. A single calendar year will always have at least two lunar eclipses and two solar eclipses, but sometimes there are more. Remember, though, that not all eclipses can be seen from everywhere.

The most eclipses that can occur in a single year is seven, but that is rare. We last experienced seven eclipses in one year in 1982, and it will happen again in 2038. For seven eclipses to occur in a single year, the first must be in early January, then the last will be in December.

The reason eclipses don’t happen at the same time every year is because their occurrence is based on the lunar cycle, or lunar months, which lasts 29.53 days. Our months last between 28 and 31 days, so while the lunar cycle remains constant, it does not always match up the same on our calendar.

They won’t be happening forever

Lunar eclipses have been occurring for thousands of years, but they won’t last forever. This is because the moon is slowly drifting away from Earth. At some point, it will no longer be close enough to Earth to cast a full shadow on our home planet.

The moon is moving away from Earth very slowly, so the end of lunar eclipses won’t be any time soon. It’s only drifting away at a rate of about 1.5 inches per year, about the same rate at which our fingernails grow. At that rate, it will take about 600 million years before it is too far away to fully cast a shadow on Earth, ending lunar eclipses.

The moon is moving away from Earth because of the tides here on our planet. The gradual movement is thought to have been occurring since the moon first formed about 4.5 billion years ago. While the movement is slight, it is making Earth slow down.

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