The moon will illuminate our sky again this week, traveling from its first quarter phase to full moon, and it’ll be hard to miss.
But next Sunday night and Monday morning, the moon will experience an eclipse that few, if any, sky watchers will even notice: a penumbral eclipse.
Eclipses of the moon are pretty simple to understand. As the moon orbits the Earth, it occasionally enters the shadow of our planet and we see a lunar eclipse.
This can occur, of course, only when the moon is full; in other words, when it’s opposite the sun in our sky.
What most folks don’t know, however, is that every solid body casts not one, but two shadows — a dark inner shadow that everyone can see (this is called the “umbra”), and a light outer shadow that’s tough to notice unless we look for it (the “penumbra”).
Check it out for yourself using a bright lightbulb to cast the shadow of your hand onto a wall. If you look carefully, you will see both shadows: the dark inner shadow and the faint outer shadow that forms a blurry fringe around the umbra.
It’s this penumbral shadow of our planet that the moon will drift through early next week, and we in North America are in prime viewing position.
Frankly, though, there won’t be much to view. The eclipse will begin at 9:53 p.m. PDT Sunday, March 24, but only the most observant of moon gazers will see anything change on the moon’s face for the next hour or more.
Only around maximum eclipse (12:13 a.m. PDT) might you see a bit of darkening around the moon’s bottom edge. That’s because, around that time, the moon’s southernmost limb is closest to the umbral shadow, so it tends to darken more.
The moon will then continue to leave the penumbra until the eclipse officially ends at 2:33 a.m. PDT.
If you miss this lunar eclipse — and many of us will due to its subtlety — our next chance to see the moon enter the Earth’s shadow will come on the night of Sept. 17/18.
It’ll be a similar eclipse, but on that night the moon will enter the umbral shadow — just barely, though, so we’ll be able to see a tiny partial eclipse.
The next total lunar eclipse will occur for us in North America next year at this time, on the night of March 13/14, and that’s the one that most of us are excited about.
We in North and South America will be in a great location to view it high in our sky. Our friends in Asia will watch the eclipse as the moon rises, while those in Europe and western Africa will see the total eclipsed moon setting in the west at dawn.
In just two weeks, however, the moon will be co-starring in the most spectacular of all eclipses: a total solar eclipse that you shouldn’t miss. More about that next week.
In the meantime, be sure to check out the penumbral show next Sunday night!