Scrawl a big circle around the date Jan. 31. That Wednesday morning, the full moon will toddle into Earth’s shadow and be eclipsed. Unlike the August solar eclipse, where you had to be standing inside a 100-mile-wide strip to see totality, total lunar eclipses are visible across half the planet anywhere the moon is up.
A full moon always lies opposite the sun in the sky, so it rises at sunset and sets at sunrise. Because the moon’s orbit is inclined to Earth’s orbit and Earth’s shadow at the moon’s distance only covers a little bit of sky (just 2.5°), the full moon almost always misses the target, sliding either above it or below it. But a couple times a year, the moon crosses the flat plane of Earth’s orbit at the same time it’s full. Then, sun, Earth and moon lie exactly in a line, the moon moves into the shadow, and we see an eclipse.
Wednesday’s eclipse is unusual and more challenging than some because it occurs at dawn for the eastern half of the country with the moon quite low in the western sky. In the Eastern time zone, observers will see the moon set in a deep partial eclipse shy of totality. The situation improves for the Midwest, where both partial phases and the start of totality will be visible.
The farther west you live, the higher the moon will be and the more of the eclipse you’ll catch. Observers in the Pacific time zone will see the whole thing, only contending with twilight as the moon leaves the shadow.
Earth has two shadows, umbra and penumbra. The umbra is the dark inner part, where the orb of the Earth completely blocks the sun from view. The outer shadow or penumbra is where the Earth partially blocks the sun — the sunlight that gets through lightens the shadow to a pale gray. You can picture this by holding your hand up to block the sun on a sunny day. If you completely block the sun’s disk, your face is in shadow. But if you only block half the sun, your face is in partial shadow.
Most people ignore the moon’s passage through the penumbral shadow en route to the umbra because it’s more subtle darkness compared to the black bite of the umbra. But I encourage you to watch for it. At the very start, it’s too pale to see, but you’ll notice a distinctly dusky shading across the top half of the moon about a half-hour before the partial eclipse begins.
As the moon treads into the umbra, partial eclipse officially begins. All lunar eclipses are perfectly safe to watch from start to finish, so have at it with eyeballs, binoculars and telescope. Normally, the sky darkens as the moon dips into shadow, but the opposite will happen at least for the eastern half of the country. Dawn will brighten the sky during its progress.
Here are the specific times (Central time) for the different phases of the eclipse. Add an hour for Eastern, subtract an hour for Mountain and subtract two hours for Pacific. For observers in the Central time zone, the moon will be faint in a bright sky at the start of totality — be sure to use binoculars to help you spot it.
Partial eclipse begins — 5:48 a.m.
Total eclipse begins — 6:51 a.m.
Mid-eclipse — 7:30 a.m.
Total eclipse ends — 8:08 a.m.
Partial eclipse ends — 9:12 a.m.
One thing you’ll see clearly is the moon’s changing color. Depending on the transparency of the atmosphere, which is affected by clouds, smoke and volcanic dust, the moon’s color varies from bright copper to muddy-gray. With no major volcanic eruptions in progress, I suspect this eclipse will be on the orange side. Speaking of color, the Jan. 31st full moon is the second of the month, which by current interpretation makes it a Blue Moon. That’s not all. Full Moon occurs only about a day from perigee, the moon’s closest approach to Earth, so this will also be a supermoon. Add it all up and you’ve got a Super Blue Moon!
Since the moon will be low in the sky from many locations with dawn providing just the right illumination of the scene, this eclipse may well be a photographer’s dream. For once, we can get the colorful moon and a nice foreground together in the same picture! Experiment with different exposures by checking your camera’s rear display screen until you get the right balance of light between the fading moon and brightening foreground scene. Don’t forget a tripod!
Why should the moon have any color at all if it’s inside dark shadow? If the Earth had no atmosphere, it would be perfectly black; we’d only know it was there by the stars it blocked from view. Sunlight squeaks around the edges of the Earth because the atmosphere acts like a prism and bends or refracts sunlight into the shadow. Because that light is streaming along the Earth’s edge at a very shallow angle, the greens and blues are scattered away, leaving only reds and oranges to spill into the shadow cone. From the perspective of someone standing on the totality eclipsed moon looking back toward the Earth, they see a darkened globe rimmed in a red glow comprised of 360° of sunrises and sunsets around the globe. What a sight awaits future astronauts!
I hope your sky is clear. This will be the only eclipse of any kind for the U.S. this year; the next total lunar happens on Jan. 20-21, 2019 with the moon high in the evening sky.