Penumbral Eclipse

This year will offer up some great skywatching sights, including a brilliant showing by Mars, and the closest encounter between the planets Saturn and Jupiter in centuries. But it won’t offer good eclipses. There are no total lunar eclipses visible anywhere on the planet. The only lunar eclipses are so faint that they’re hard to see at all.

The first of them takes place today. It’ll be visible mainly across the eastern hemisphere. From the U.S., it’ll be in progress at moonrise across most of Alaska, but that’s about it.

This is known as a “penumbral” eclipse. The Moon will pass through Earth’s faint outer shadow — the penumbra. The shading is so faint, though, that most people won’t notice it.

All lunar eclipses belong to a cycle known as a Saros. The circumstances of each eclipse in the cycle repeat every 18 years and 11 days. There are only a couple of differences. One is that each eclipse is visible about a third of the way around Earth from the previous one. And the other is that the Moon moves slightly southward on each eclipse, so it passes through slightly more of Earth’s shadow.

This cycle began in 1749, with the first of a series of penumbral eclipses. It’ll soon move to partial eclipses, then total eclipses, where the Moon is totally immersed in the shadow. The first of those will take place on July 4th of 2308.

The Moon then begins moving out of the shadow. The cycle will end with a final penumbral eclipse — in 3011.

Script by Damond Benningfield