If you’re in the United States, today’s the day of the big solar eclipse. Offhand, I can’t recall a solar eclipse with this much hype. Yes, they’re rare, and yes, I’m looking forward to it, but I don’t recall another with this much buzz. There’s even eclipse memorabilia that has nothing to do with viewing it; I’ve never seen that before.
This is also the first time I’ve seen solar filters on sale in stores. Back in ye olde days, we were taught how to make a simple device where we could stand with the sun to our backs and project an eclipse onto a piece of paper. That’s still perhaps the safest method, as at no time you look directly at the sun. Yes, you can go blind watching a solar eclipse without solar filters, and people have, and no, sunglasses don’t work, and no, welding goggles aren’t a solution because many of them aren’t dark enough.
Worse, there’s reports of fake solar filters on sale. This link is to the a page by the American Astronomical Society on how to tell if your solar filter is safe.
I have a pair of real solar filters, and even those say to use them for no more than three minutes continuous use. If you have a pair, check to make sure they’re real and follow the directions that come with them. Even then you have to be careful. If they’re damaged or light leaks around them, you can still damage your eyes.
This brings up a point a friend raised last Friday. He asked what you would see through a pair of solar filters, and I had already tried mine to see if they’d work, and I described the dim disk of the sun and how we’d see the black disk of the moon slowly sliding across. He said “If that’s all you’ll see, why risk your eyes?”
He has a point. You can safely observe a solar eclipse without looking at the sun. All it takes are two plain index cards. You make a tiny pinhole in one, use the other as a screen, and, with your back to the sun, hold the index card with the pinhole above the other and move it back and forth until you get a bright circle. You’ll be able to see the dark disk of the moon move across the sun without looking at the sun at all.
Don’t look through the pinhole at the sun! That’s not what it’s for, and it will damage your eyes! Don’t project the sun on a reflective surface! That will damage your eyes, too!
Again, do not look at the sun without the correct solar filters! It will damage your eyes!
What holds for our eyes also holds for our cameras and smart phones. Yes, they, too, can be damaged by taking a picture of the sun without solar filters. I wonder how many will get burned out today. I’ve also seen warnings about pointing optics like telescopes at the sun without solar filters. There’s nothing “magic” about solar eclipses; the sun is just that bright.
Solar eclipses are interesting things. Ours is the only planet in the solar system with a moon at just the right apparent diameter to cover the apparent diameter of the sun. Even then, it’s not always perfect, otherwise, we’d have a solar eclipse with every new moon. The moon is in an elliptical orbit about the earth (well, about a common gravitational point, but that’s another topic), and is inclined in respect to the earth’s orbit around the sun, and the earth also travels around the sun in an elliptical orbit, and all of it put together means that you don’t get a solar eclipse every month. Everything has to be lined up just right to have a total eclipse. Thus you end up with partial eclipse, where the sun doesn’t quite cover the moon, or an annular eclipse, where the moon appears smaller than the sun and you have a bright ring of light around the dark disk of the moon. Many times the moon doesn’t move across the sun at all. When it does, it seems to move across in one place and not another, which is why there’s a total eclipse visible in the US today, and not in Argentina. It’s all fascinating stuff.
It also brought to mind a famous event that happened in the Middle East nearly two thousand years ago. Here’s one account:
“And it was now about the sixth hour, and a darkness came over the whole land until the ninth hour, the sun’s light failing; and the veil of the temple was rent in the midst.”
That’s from the Gospel of Luke, Chapter 23, verses 44-45, the ASV translation.
One of the neat things about records of astronomical events is that they lend themselves to date calculation. That’s how some have dated the birth of Jesus, because, according to Josephus, there was a lunar eclipse visible in Jerusalem the year Herod the Great died. Since Jesus was born before Herod the Great died, that helps us to estimate the date. Except we now know that lunar eclipse seen in the usually attributed year wasn’t total and may not have produced the effect of the moon turning to blood, which you get in a total lunar eclipse. And some, even in the 1st Century, attributed the period of darkness at the crucifixion of Jesus to a solar eclipse. That’s come to mind with this one, since the duration from start to end is close to three hours, the same time span noted by Luke.
Except, even in the time observers noted the period of darkness, there was known to be a problem associating it with a solar eclipse. The Christian historian Sextus Julius Africanus, in discussing this period of darkness, mentions that the historian Thallus attributed this to an eclipse, and the historian Phlegon recorded a solar eclipse from the sixth hour to the ninth during the full moon during the reign of Tiberius Caesar. Africanus said it was called an eclipse “without reason.” But why?
Think of how solar eclipses happen: from some point on the earth, the moon must move across the face of the sun. This means that solar eclipses can only occur during a new moon. The moon’s phases are caused by the position of the moon in respect to the sun. A full moon occurs when the moon is on the opposite side of the earth from the sun, and we see a completely illuminated disk. A first and last quarter moon occurs when the moon is at right angles in respect to the earth from the sun, so we only see half the moon illuminated, and the other half in darkness. In a new moon, the moon is on the same side of the earth as the sun, and appears as a dark disk, and most of the time we can’t see it at all.
What does this have to do with the darkness during the crucifixion? Everything. Jesus was crucified at the start of Passover. Passover begins on the 15th of the Jewish month of Nisan. Judaism uses a solar-lunar calendar, with each month beginning with the new moon. Each phase of the moon – new; first quarter; full; last quarter – is roughly seven days apart. Thus, Passover, being 15 days after the new moon, occurs at the full moon. Since the moon is on the opposite side of the earth from the sun during a full moon, it could not have been a solar eclipse.
Today, in the path of totality all across the United States, the sun’s light will fail. Nearly two thousand years ago, it failed for a different reason.