The night sky on Tuesday will treat us to a partial lunar eclipse during a supermoon. It's an astronomical wonder that almost anyone in the Western Hemisphere can experience, and it's the latest reminder that our home planet is part of a bigger cosmic system.
The night sky on Tuesday will treat us to a partial lunar eclipse during a supermoon. It's an astronomical wonder that almost anyone in the Western Hemisphere can experience, and it's the latest reminder that our home planet is part of a bigger cosmic system.
When is the lunar eclipse, and where can I see it?
This lunar eclipse will happen between 8:41 p.m. Eastern time Tuesday and 12:47 a.m. Wednesday, with the maximum partial phase occurring at 10:44 p.m. It will be visible across most of the United States, Canada, Latin America and the Caribbean, Africa and Europe.
Bruce Betts, the chief scientist at the Planetary Society, will be watching the show from his front yard in Pasadena, California.
Eclipses offer a chance to feel "the three-dimensional nature of everything," Betts said. "It's something that just in a visceral way is like, wow."
What causes a lunar eclipse?
Lunar eclipses are caused by an alignment of the sun, Earth and moon. Unlike April's solar eclipse, when the moon blocked the sun, this time the Earth's shadow will spill over the moon, blocking some or all of its illuminated surface.
There are three types of lunar eclipses. During a penumbral eclipse, which last happened in March, the moon passes through only the outer part, or penumbra, of Earth's shadow. This causes the moon's face to dim slightly.
A total lunar eclipse, on the other hand, happens when the moon is swallowed by the darkest part of Earth's shadow, the umbra. In this scenario, the lunar surface glows red in what is known as a blood moon.
And then there are partial lunar eclipses, like the one viewers will see Tuesday evening if the sky is clear. Only a portion of the moon will pass through Earth's umbra, blackening out a chunk of its face.
"You'll see the shadow of the Earth start to eat into the moon," Betts said, "like taking a small, dark bite out of the moon."
But, he added, be sure to limit your expectations: Only 3.5% of the lunar surface will be blotted out during Tuesday's eclipse.
You may wonder if such a limited lunar eclipse is really impressive.
"It's still worth seeing," Betts said. "But if it's cloudy, you don't have to be too sad."
He recommends that while you're out moongazing you take a moment to scan the night sky for familiar planets and constellations. "It's worth a look-see," he added.
How do you observe a lunar eclipse?
Anyone on the night side of the planet can watch the lunar eclipse, though the sight will be better in darker locations. It will be visible with the naked eye, but binoculars or a telescope can be used to zoom in on finer details of the moon during the event.
The most dramatic part of the show, when Earth's umbra obscures a portion of the lunar surface, will last about an hour. Before and after this, the moon will pass through Earth's penumbral shadow, during which its surface will remain full, but with dampened brightness.
The penumbral phases of the eclipse will each last about an hour and a half.
How much of the eclipse you will be able to see depends on where you are. In North America, sky watchers on the West Coast will miss most of the first penumbral phase because the moon will be below the horizon. But those on the East Coast will be able to see the entire event.
September's full moon is a supermoon. These are the biggest and brightest full moons, because they occur at the point of the lunar orbit that is closest to Earth. And this month's is actually the second of four consecutive supermoons this year.
The most recent supermoon, which was also a blue moon, occurred on Aug. 19. The next two supermoons will take place on the evenings of Oct. 17 and Nov. 15.
Are there more astronomical events coming up?
Lunar eclipses always precede solar eclipses, which occur when the moon orbits to the Earth's other side, ending up directly between our planet and the sun.
The forthcoming solar eclipse won't be much like April's widespread event: On Oct. 2, an annular solar eclipse will be visible only from the Pacific Ocean and the tip of South America.
Next March, a total lunar eclipse will grace the night skies of Western Europe, Western Africa and the Americas.