Since you’re reading this column, you may be one of the few who is treated to an interesting celestial phenomenon this week: a partial eclipse of the moon.
The reason most will miss it is because this eclipse isn’t a biggie. In fact, less than 9% of the moon’s diameter will be covered by the Earth’s dark shadow.
When I say “partial” eclipse, I’m not joking!
You may already know that solid objects like the Earth cast two shadows: a dark, inner one known as the “umbra,” and a light outer one known as the “penumbra.”
You can demonstrate this for yourself by finding a bright light bulb and casting the shadow of your hand onto a wall.
What is most obvious is the dark, inner umbral shadow, but look carefully around its edge. There you’ll see the lighter, blurrier penumbral shadow.
When it comes to casting a shadow, the Earth is no different than your hand, except that its shadow extends more than 800,000 miles into space, well beyond the orbit of our moon.
And, on the night of Tuesday, Sept. 17, the full moon will drift into these shadows and produce an eclipse we can see from here.
Don’t expect too much, though. While the moon will pass completely into the Earth’s penumbral shadow, you may notice nothing different about the moon’s appearance.
The “big show” comes later, when the moon barely skims along the bottom of our planet’s umbra.
This occurs during the early evening hours, but when you see it will depend on where you are.
Skywatchers on the East Coast will see the umbral shadow first falling onto the very top of the moon around 10:12 p.m., with the moon midway up in the eastern sky.
Because of time zone differences, the eclipse will be seen earlier the farther west you are; those on the West Coast will watch the umbral phase begin at 7:12 p.m., not long after the moon has risen.
The whole thing will appear to end 64 minutes later, even though the moon will remain engulfed by the penumbral shadow for another 1½ hours.
Unlike an eclipse of the sun, a lunar eclipse is perfectly safe to watch without a protective filter.
All you need is your eyes, though viewing with binoculars or a small telescope can be fun as well.
And, unlike many celestial phenomena, you won’t need to drive to a dark site far from city lights; you’ll be able to see it from just about anywhere.
To see a preview of this eclipse from your location, visit timeanddate.com and click on “Sun, Moon & Space.” Then, in the dropdown menu, click on “Partial Lunar Eclipse.” Here you can select the eclipse you’d like to see and even enter your location to produce a great simulation.
If clouds or a memory lapse causes you to miss it, you’ll have to wait only until the night of Thursday/Friday, March 13/14, 2025, for the next one.
On that night, the moon will become engulfed entirely by the Earth’s umbral shadow and will provide all of North America with a stunningly beautiful total lunar eclipse.
