Seems like every cool astronomical event happens on a Friday lately. Tomorrow night, the Full Hunter’s Moon takes a dip in Earth’s shadow across much of the Americas, Europe, Africa and West Asia. Between 4:53 and 8:48 p.m. CDT 3/4 of the lunar disk will be eclipsed by the planet’s outer shadow or penumbra. Penumbral eclipses are cousins of the more familiar and dramatic total lunar eclipses.
For any lunar eclipse to happen, the moon must be full and the sun, Earth and moon precisely lined up in that order. In this arrangement, the full moon drifts directly into Earth’s shadow producing a lunar eclipse.
Wish it were that easy every full moon. Because of its tilted orbit, the moon misses Earth’s shadow during most full moons and instead we see … a full moon. But several times a year, the moon happens to be full at the very hour it’s exactly aligned with sun and Earth. Voila! Its shiny disk is quenched by shadow.
Earth’s shadow has two parts – umbra and penumbra – making three types of lunar eclipses possible:
* Total – where the moon passes completely into the Earth’s umbra or inner shadow. This variety is the most highly anticipated. Deeply reddened sunlight bent by Earth’s atmosphere filters into the shadow, transforming the moon into a dramatic coppery disk. Amateur astronomers have been known drive up to several hundred miles to see one. Don’t ask me how I know this – I just do.
* Partial – a near but not exact lineup where only a portion of the moon drifts through the inner shadow, giving it the appearance of a cookie with a bite out of it.
* Penumbral – Completely misses the inner shadow but glides through the penumbra or outer shadow. Because a portion of the sun shines into the penumbra, it’s not nearly as dark as the umbra. That’s why penumbral eclipses are subtle compared to partials and totals.
Friday’s eclipse occurs during early evening hours for North America (midnight-1 a.m. in Europe); no setting of alarm clocks is required.
Some penumbral eclipses, those where the moon only dips a toe in shadow, are barely noticeable. Not this one. At maximum eclipse (6:50 p.m. CDT), 76 percent of the moon will take the penumbral plunge. At the very least, you’ll notice that the right side of the moon (as seen from North America) looks gray and out of round.
For many of us, maximum eclipse will occur when the moon is low in the eastern sky shortly after sundown. That means you’ll need to plan ahead to find a place with a clear view in that direction. Bring a camera. The scenic potential of the moon rising in Earth’s purple-gray shadow while in penumbral eclipse is worth burning up a few dozen frames.
In Europe, the moon will fly high in the south at eclipse time and be ideally placed for viewing, though lacking in sunset scenery potential like that in the U.S.
We’ve been living on meager eclipse rations for some time now in the Americas. That changes next year when two total lunars will darken the sky – the first on April 15 and a second on October 8. Get ready for more tales from the shadow world!
Just a quick note. I’ll be working on other projects in the next few days, so if you come by and don’t see a daily update you’ll know why.