This Friday, July 27, most of the world will be treated to a record-breaking, blood-red lunar eclipse. It will be the longest of the century, clocking in at one hour and 43 minutes—only four minutes short of the absolute maximum. Here’s what you need to know about the celestial event.
What is a lunar eclipse?
A lunar eclipse occurs when the Earth passes between the sun and the moon and casts a shadow on the moon’s surface. It’s the reverse of a solar eclipse, in which the moon crosses between the Earth and the sun. In a total lunar eclipse, like this one, the moon will move from a phase of partial eclipse, to the total eclipse, to another partial eclipse, all in about four hours (give or take a few minutes, as the moon will look dark a bit before and after the actual eclipse).
Why is it so long?
There are three reasons. First, the Earth is unusually far away from the sun, which allows it to cast a wider shadow for the moon to pass through. Second, the moon is positioned to travel through the middle of this shadow, giving it the longest possible path. Finally, the moon is pretty far from the Earth right now (it’s in the “micromoon” phase), meaning that it will take longer for it to travel through the shadow.
If all of these oddities were maxed out—the Earth was as far as possible from the sun, the moon was as far as possible from the Earth, and the moon traveled right through the middle of the shadow—the eclipse would hit the perfect one hour 47 minute mark (the record is one hour, 46 minutes, and 36 seconds from 318CE).
(Coincidentally, the shortest lunar eclipse of the century took place a few years ago.)
Still, the combination of these three factors to this degree is quite rare—according to Accuweather, there won’t be a longer eclipse until more than a century from now, in 2123.
Why is it so red?
All total lunar eclipses are red, giving them the informal title “blood moons.” The color comes from the fact that during the lunar eclipse, the moon doesn’t receive any direct sunlight. Instead, it gets indirect sunlight that’s refracted around the Earth, which must first pass through the Earth’s atmosphere. Longer wavelength light—think red, or orange—passes through the atmosphere more effectively than violet or blue, allowing it to reach the moon, reflect back, and provide the signature blood-colored tint.
When will it be?
The first partial eclipse will begin at 6:24 PM UTC (2:24 PM EST), and the total eclipse will begin about an hour later, at 7:30 PM UTC (3:30 PM EST).
Where can I see it?
If you live in North America, unfortunately, you won’t (unless you happen to live in a lucky sliver of Newfoundland, Canada). Most of the world, however, will be able to catch a glimpse of this rare event. Africa, the Middle East, and Southeast Asia will have the ideal view—one NASA scientist told ABC that either Ethiopia or the middle of the Indian Ocean has “the best seat in the house”—but eclipse-seekers living anywhere from South America to Australia will be able to see some part of the phenomenon.
If you can’t make it to one of these locales, fear not: the astronomy education website Slooh will be live streaming the eclipse.
When’s the next total lunar eclipse?
The next total lunar eclipse will take place on January 21, 2019 (although it’ll only last an hour and 2 minutes)—and North America will have a great view of this one. The next partial eclipse will happen about six months later, on July 16.
Do I need safety glasses?
Viewing a lunar eclipse doesn’t require looking at or near the sun, so safety glasses aren’t necessary—that is, if you’re the kind of person who cares about safety warnings at all.