Lunar eclipse 2021: How to watch the blood moon, supermoon, and lunar eclipse

Brian Resnick is Vox’s science and health editor, and is the co-creator of Unexplainable, Vox's podcast about unanswered questions in science. Previously, Brian was a reporter at Vox and at National Journal.

On May 26, the Earth will pass between the sun and the moon, casting a shadow across the moon’s surface and making it appear a deep red color for 14 minutes and 30 seconds. Around moonset — right before sunrise — the West Coast of the United States will be able to see a nearly total eclipse. Many parts of the Americas and Asia will be able to see a partial eclipse. And if you’re in Eastern Australia, you’re in luck: The entire eclipse will be visible to you.

If you’re in an area that can see the eclipse, its total phase will begin at 11:11 Coordinated Universal Time (UTC) on May 26 and end at 11:25 UTC. (This will be after sunrise for many parts of the world. Convert UTC to your local time here.) On the night of the full moon, the moon rises in the east after the sun sets and then sets in the west before the sun rises. This will be the first total lunar eclipse since 2019.

As a consolation for those who can’t see the total eclipse, the moon will also be near its closest approach to Earth, making it a “supermoon” — meaning it will appear slightly larger in the sky for everyone on Earth. (This happens once in every 14 full moons or so.)

Whether or not you can see the eclipse, it’s still a cool phenomenon. Here’s how and why it happens.

Why do we have lunar eclipses?

The simple answer is “because the moon sometimes passes through the shadow of Earth.” But there’s more to it than that.

Eclipses have to happen during a full moon. When the moon is full, it means the sun, Earth, and moon are in alignment.

Now, you might be thinking: “Why don’t we have lunar eclipses every full moon?”

The moon’s orbit isn’t perfectly matched up with Earth’s. It’s tilted 5 degrees.

No one is completely sure why, but it might have to do with how the moon was likely formed: from a massive object smashing into Earth.

The nodes are located at two directly opposite points in the moon’s orbit.

This means during most full moons, the shadow misses the moon, as you can see in the diagram above. But there are two points in the moon’s orbit where the shadow can fall on Earth. These are called nodes.

For a total eclipse to occur, the moon needs to be at or very close to one of the nodes.

An animate graphic shows the moon lining up between the Earth and the sun at a node.

When the sun, Earth, and moon are aligned at a node, voilà!

The moon falls into the path of Earth’s shadow.

There are usually two or three lunar eclipses in a given year, and everyone lucky enough to be on the night side of Earth has a chance to witness it.

You don’t need any special equipment or protective glasses to view one (unlike with a total solar eclipse). But a pair of binoculars will give you a better, more detailed view of the moon’s geography as it darkens in shadow.

What’s a supermoon?

The moon’s orbit around Earth is not a perfect circle. It’s an ellipse that’s longer than it is wide. As the moon follows this orbit, it’s sometimes closer to Earth and sometimes farther away. At perigee, the closest spot in its orbit to Earth, it’s around 31,068 miles closer to Earth than at apogee, when it’s farthest away.

Meanwhile, we see different phases of the moon — full, crescent, waxing, and waning gibbous — depending on whether the sun-facing side of the moon is facing the Earth.

A supermoon occurs when these two cycles match up and the full moon coincides with its perigee, making it appear slightly larger and brighter in the sky. This occurs about one in every 14 full moons, Jim Lattis, an astronomer at the University of Wisconsin Madison, notes.

The difference between a normal full moon and a supermoon isn’t all that significant. As Neil deGrasse Tyson put it on the StarTalk radio show: “If you have a 16-inch pizza, would you call that a super pizza compared with a 15-inch pizza?” For the most part, NASA explains, the differences between a normal full moon and a supermoon “are indistinguishable” to the human eye.

The supermoon doesn’t have any astronomical significance other than making for a slightly larger target for backyard astronomers to look at.

Why does the moon turn red during a lunar eclipse?

blood moon — A 2014 lunar eclipse, as seen from Southern California.

During a total solar eclipse — like the one North America saw in the summer of 2017 — the entire brighter-than-bright disc of the sun turns black, revealing the sun’s atmosphere.

What happens during a total lunar eclipse is a bit less dramatic, but beautiful nonetheless. When rays of sunlight pass through the Earth’s atmosphere, its gases trap and scatter the blue light in the spectrum. (This is why the sky appears blue.) The red, orange, and yellow wavelengths pass into Earth’s shadow and get projected onto the moon.

Basically, a total lunar eclipse is like projecting all the sunsets and sunrises onto the moon. If you’re in the path of the eclipse on May 26, that’s what you have to look forward to.

Watch: Eclipses, explained

Correction, June 10: A previous version of this story misstated the date of a solar eclipse that was visible from North America.

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