Look fast! The shortest total lunar eclipse of the century takes place on Saturday, and the most reliable way to see it may well be online. That's especially true if you live in the half of the world where the sun will be shining.
NASA says the full moon will darken to a dusky red between 7:57 and 8:02 a.m. ET Saturday. Skywatchers on America's East Coast will miss out on totality because the moon will have set by that time. But at least the buildup will be visible: Just before sunrise, Easterners (and folks in western South America) can watch our planet's shadow creep over the moon's disk. That creeping partial phase begins at 6:16 a.m. ET.
The western U.S. should be able to catch the entire total phase. The event will also be visible in Asia and the Pacific, to varying degrees — but Europe and Africa will be shut out completely.
Lunar eclipses are totally different from solar eclipses: First of all, it's safe to gaze at the moon during every phase of the event, and it can be fun to watch through binoculars or a telescope. What's more, an entire hemisphere can see it simultaneously — depending on the weather, of course.
During a solar eclipse, the moon comes between the sun and Earth. During a lunar eclipse, Earth comes between the sun and the moon. But even during the total phase of a lunar eclipse, Earth's atmosphere refracts enough sunlight to throw the reddish glow of countless sunsets onto the full moon's surface. That's why a total lunar eclipse is often called a "blood moon."
The course of an eclipse depends on the precise orbital path that the moon follows in its orbit. If the full moon passes outside Earth's shadow, there's no eclipse. This weekend's total eclipse is so brief because the moon traces a path that barely goes through our planet's full shadow, also known as the umbra. NASA's calculations suggest totality will last less than five minutes, while the U.S. Naval Observatory goes with a duration of 12 minutes (7:54 to 8:06 a.m. ET). Either way, it's darn short.
There's another quirk that makes this eclipse worthy of note: It's the third in a series of four lunar eclipses over the course of 18 months, a phenomenon that astronomers call a "tetrad."
"The most unique thing about the 2014-2015 tetrad is that all of them are visible for all or parts of the USA," NASA's Fred Espenak said a year ago when the first eclipse in the series occurred. The next such tetrad unfolds in 2032-2033, when Australians will have the best seats in the house.
You don't have to be in the eclipse zone to get in on the fun. Here's a roundup of Saturday's online events:
- The Griffith Observatory in Los Angeles will provide video views of the lunar eclipse via Livestream from 5 to 9:30 a.m. ET (2 to 6 a.m. PT).
- The Slooh online observatory will put on a webcast featuring eclipse imagery from several venues, plus commentary from Bob Berman, Will Gater and Eric Edelman. The show starts at 6 a.m. ET. Use the hashtag #BreakfastEclipse to tweet questions to the hosts.
- The Virtual Telescope 2.0 website will stream eclipse imagery starting at 6 a.m. ET, thanks to team members from Australia, Panama, Costa Rica and the United States. Italian astrophysicist Gianluca Masi is the coordinator and lead commentator.
- NASA's Marshall Space Flight Center will have astronomer Mitzi Adams on hand to answer questions via the @NASA_Marshall Twitter account, starting at 6 a.m. ET. Tweet questions with the hashtag #Eclipse2015. Keep an eye on Marshall's Ustream video channel as well.
Got pictures? Please share them with us by using the hashtag #NBCeclipse on Twitter or Instagram. We'll put together a selection of eclipse pics after the big event. The next total lunar eclipse takes place on Sept. 28.