BACKGROUND | NATIONAL GEOGRAPHIC
At the same time, the moon will be at perigee—the lunar orb’s closest approach during its egg-shaped orbit around our planet—creating an eclipsed “supermoon.”
Lunar eclipses happen when the full moon, Earth, and the sun are lined up so that the moon crosses through Earth’s shadow. (See lunar eclipse pictures.)
“It’s a very cool kind of thing to see. It gives us an almost 3-D feeling for space that we don’t normally get,” said Mark Hammergren, an astronomer at the Adler Planetarium in Chicago.
Coined in 1979, the term “supermoon” is often used to describe a full or new moon that coincides with perigee—something that happens about once a year, on average. (Related: “Titanic Sunk by ‘Supermoon’ and Celestial Alignment?”)
We don’t see an eclipse with every full moon because our natural satellite follows a tilted orbit around Earth. This tilt also means that an eclipse can be full or partial, depending on how much of the lunar disk falls in our planet’s shadow.
The last total lunar eclipse was in December 2011, and the next one doesn’t happen until April 2014.
Monday’s partial eclipse will be visible to sky-watchers in most of North and South America during the early hours before sunrise.
Meanwhile, observers in Australia, the eastern parts of Asia, and across the Pacific Ocean will see the partial lunar eclipse Monday evening just after sunset.