Lunar eclipse is worth staying up for


By Tom Burns - Stargazing



I usually jump with excitement at the chance of announcing a total eclipse of the moon. This time, I have serious reservations, based partly on the date and partly on the hype surrounding this particular event. Therefore, for the record, look for it during the night of Sunday, Jan. 20, from 10:33 p.m EST until 1:50 a.m., which is technically Monday, Jan. 21.

A lunar eclipse happens when Earth is positioned directly between the sun and the moon. Earth’s shadow blocks the light from the sun that normally illuminates the full moon.

Starting at about 10:33 p.m., the moon will pass into the Earth’s shadow and slowly disappear over the next hour and eight minutes. It will look like a giant monster is taking larger and larger bites out of a cosmic cookie.

By 11:42 p.m., the entire disk of the moon will be obscured. At that point, the full moon will glow anywhere from ashen gray to bright orange depending on the sky conditions. At their best, past eclipses I have seen have been a dark, coppery red and looked to my eye like a bloody fingerprint in the sky.

Luna will remain in that state of total eclipse for over an hour. The middle of totality occurs at 12:12 a.m. At that point, the moon will be at its darkest and most beautifully creepy.

Luna will begin to reappear at 12:43 a.m. as a thin crescent. Over the next hour, the bright portion of the moon will appear to get larger and larger. By 1:50 a.m., the bright disk of the full moon will have returned, and the eclipse will be over.

What a pleasure it is to describe an astronomical event that doesn’t require a telescope as big as a corn silo to see and doesn’t demand that you drive to the dark, rural skies of Middle-of-Nowhere, Ohio. The binoculars you were born with, your own two eyes, are all you need.

However, this particular eclipse leaves me with mixed feelings.

First of all, the eclipse is happening in January. Even if it isn’t frigid that night, the chances for a clear sky are relatively remote during our Ohio winter months. But you knew that already.

As a result, I’m not going to drive to some remote location to see this one. A quick glance out the window of my house at 11:38 p.m. will tell me if it’s worth the trouble of venturing as far as my backyard.

In that regard, please note that Perkins Observatory is not hosting a program for the event. Assuming it’s clear, you can see this one very well indeed from your own backyard.

My second reservation arises from the extraordinary hype that has arisen from the usual purveyors of astronomical exaggeration. I’m referring to you, NASA, and all the media outlets that take your puffery as gospel.

Thus, the headlines scream about a “Blood Super Moon.”

Let’s start with the “Super,” which refers to the fact that the eclipse is happening during a so-called “supermoon.”

The term supermoon indicates the appearance of the moon when it is full and the moon happens to be at perigee, the closest point in its orbit around Earth. Since the lunar cycle doesn’t divide evenly into the year, perigee and the full moon coincide only a couple of times per year at best. As a result, the attention-starved publicists at NASA rush to their computers and claim that the moon will look larger by as much as 14 percent.

Technically, they are correct. The moon looks 14 percent larger than it would at apogee, Luna’s farthest point from Earth. If you observed the full moon the previous month or the month after and compared it with the supermoon, the difference would be imperceptible.

However, you might be thinking, “But I went out during the last supermoon and it looked huge!”

Most folks who go out to see a supermoon do so just after sunset. All full moons rise at sunset and set at sunrise. That means that most folks see the full moon when it is very close to the horizon on a supermoon night.

The moon always appears larger when it as close to the horizon. That documented optical impression is called the “moon illusion.” It happens because the observer has an optical frame of reference in the form of local buildings, trees, and the ground below the horizon. As the moon rises, it seems to shrink because the eye doesn’t have a frame of reference.

If you don’t believe me, try this small optical experiment. On the next full moon night, go out and observe the moon just after sunset when it is close to the horizon. (It doesn’t have to be a supermoon night.) The moon will look huge.

Now go inside until just after midnight. When you see the moon then, it will be much higher in the sky and will have appeared to shrink dramatically.

The moon didn’t shrink, of course. And it didn’t get significantly farther away in just a few hours. Your eye has simply lost its frame of reference as the moon rose higher in the sky.

Now let’s consider the “blood” aspect of the “Super Blood Moon.” Since the moon is enveloped by Earth’s shadow during a lunar eclipse, you might expect the moon to disappear completely. That would be spectacular, to be sure, but it would contain none of the sublime beauty of a blood-red moon.

Luckily, Earth’s atmosphere acts like a lens and bends some of the sun’s light around Earth. Our atmosphere loves to absorb and scatter the sun’s blue light. However, the red light passes much more efficiently through it.

The scattering causes the sky to be blue. As the sun rises and sets, its light passes through a thicker cross-section of the atmosphere, which is why the sun and surrounding atmosphere appear to turn red at sunset and sunrise.

Particulate matter in the atmosphere often exacerbates the reddening. Desert dust storms, volcanic eruptions, and even high humidity can redden the sun’s light and make for spectacular sunsets and sunrises.

The moon’s reflected light is much dimmer than the sun’s radiated light. But light is light, so the same thing happens to the moon on a lesser scale. I don’t know how many times people have called me asking if an eclipse is happening on a given night because the moon is red. “Nope,” I say. “It’s just that the moon is rising and close to the horizon.”

Lunar eclipses are the ultimate example of atmospheric filtering since the sun’s light is refracted through an extremely large cross section of the atmosphere.

During an eclipse, the moon’s light filtered twice: once as the sun’s light passes through a long stretch of atmosphere and heads toward the moon and again as it bounces off the moon and passes through the atmosphere toward your eyes.

Thus, if the totality of the lunar eclipse happens at sunset or sunrise, you might just get a blood-red moon. If there is a lot of particulate matter in the atmosphere, the moon will dim even further to an ashen gray and, in extreme cases, almost disappear completely.

Unfortunately, Luna will be high in the southern sky for the entire totality, so expect a coppery red at best and a yellow-orange moon at the worst or, of course, nothing at all besides a very dark night if it’s overcast.

Let’s hope for the best. Binoculars are useful because they help you to see details like craters and lunar “seas” disappear slowly as the face of the moon is obscured. But the binoculars you were born with —your own two eyes — will produce a spectacular view of the eclipse.

The geometry of an eclipse is, I suppose, interesting to some of you. However, its emotional effect is heightened if you consider its cultural impact.

Many ancient cultures honored the moon as a goddess of fertility, a giver of life on whom humans depended for the continuance of the race and the success of their crops. Her disappearance during an eclipse was truly a terrifying event.

It looked to our forebears like a giant, invisible monster had unhinged its jaws and was slowly swallowing the moon. The monster is often depicted as a dragon, a snake, a wolf, or some other prehistoric cookie monster. Thank goodness the goddess Luna doesn’t taste very good. The monster always regurgitated it.

Some cultures didn’t depend on that. They threw spears, shot arrows, beat on drums, and yelled insults at the monster to scare it away.

And why did humans engage in those rather odd practices for 10,000 years? It always worked. The monster always upchucked their goddess. Why mess with success?

Of course, we know better now. The moon is obscured because Earth gets between the moon and the sun. As the moon moves deeper and deeper into the darkest part of the Earth’s shadow, called the umbra, the bright disk of the moon shrinks to a thinner and thinner crescent. At totality, the moon is totally covered by the umbra. It’s no big deal, scientifically speaking.

Still, it’s worth staying up for. There is something eerie, unworldly, about a lunar eclipse. The experience takes you back to your most primal ancestral fears and joys. During the deepest part of the eclipse, if your heart and mind are open, you will be transported to the African savanna or the mountains of India or the forests of Germany 10,000 years ago.

Now isn’t that worth losing a little sleep?

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By Tom Burns

Stargazing

Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.