Bad Astronomy. Misconceptions and Misuses Revealed, from Astrology to the Moon Landing 'Hoax'

Eclipses are magnificent, and they do not happen very often, but they are predictable. The Moon’s path in the sky has been charted for millennia, and ancient astronomers could predict eclipses with perhaps surprising accuracy. It’s not surprising then that historical records are full of tales about eclipses. Mark Twain even used one in his novel A Connecticut Yankee in King Arthur’s Court. In it a young man from America is transported back in time to medieval England and, through a variety of circumstances, ends up being sentenced to be burned at the stake. However, he happens to know that a total solar eclipse is about to occur and tells his captors that if they don’t release him, he’ll take away the Sun. Of course, the eclipse happens right on schedule and he is set free.

That may sound silly, but it’s based on an actual event, and none other than Christopher Columbus is in the leading role. In 1503, on his fourth voyage to America, Columbus was stranded in Jamaica, his ships too damaged to be seaworthy. He relied on the natives for food and shelter, but they soon became weary of feeding Columbus’s men. When the natives told him this, Columbus remembered that a lunar eclipse — when the Earth’s shadow falls on the Moon, turning it dark — would occur soon. Just as Twain retold the tale nearly 400 years later (with a solar instead of a lunar eclipse), the event terrified the natives, who then begged Columbus to bring back the Moon. He did, and he and his men were able to stay on the island until they were rescued.

Occasionally, events are antithetical to the Columbus story — not predicting an eclipse can get you in trouble. In ancient China it was the duty of all court astronomers to predict solar eclipses. The Chinese thought that a solar eclipse was a giant dragon eating the Sun, and if enough advance warning were given they could chase the dragon away by beating drums and shooting arrows in the sky. In 2134 b.c., as the story goes, two hapless (and perhaps apocryphal) astronomers by the names of Hsi and Ho didn’t take their duties too seriously. They knew a solar eclipse was coming, but decided to hit the tavern first before telling the emperor. They drank too much and forgot to pass on the news. When the eclipse came, everyone was caught off guard. Luckily, the emperor was able to “scare off” the dragon, and the kingdom was saved. Hsi and Ho weren’t so lucky. They were collected, thrust before the emperor, presumably chastised, and not-so-presumably had their heads cut off. Legend has it that the emperor threw their heads so high in the air that they became stars, which can be dimly seen between the constellations of Perseus and Cassiopaeia. (Today we know these two faint objects to be clusters of thousands of stars, and they’re a pretty sight through a small telescope — prettier, no doubt, than this gruesome Chinese legend might have you think.) The lesson here is still relevant today: publish first, and then head off — so to speak — to the bars.

Even today, people are superstitiously terrified of eclipses. After a total solar eclipse in August 1999 that was seen all over Europe, I had an e-mail conversation with a young woman from Bosnia, which was then suffering from terrible fighting. She was shocked and saddened to see the streets deserted during the eclipse and the signs posted to warn of dangerous rays from the Sun that would kill people exposed to them. As if these people didn’t have enough to worry about, they also had to hide in fear of something that might have actually given them a fair degree of much-needed joy.

Not all eclipse fears are so severe. There are many legends among ancient people about solar eclipses, and having the Sun eaten is a common thread. Others have seen it as a bad omen, so they pray during eclipses. Still others avert their eyes, lest they have a spell of bad luck cast over them…

…which brings us to a very interesting and somewhat controversial point about the Sun and eclipses. How many times have you heard that looking at an eclipse will make you go blind? Every time a solar eclipse rolls around, the news is full of warnings and admonitions. The problem is, they never say exactly why you can go blind, or what degree of eye damage you might suffer. Worse, they sometimes give incorrect advice on viewing an eclipse, increasing the danger.

I’ll cut to the chase: viewing an eclipse can indeed be dangerous. Obviously, looking at the Sun is very painful, and it is extremely difficult to do so without flinching, tearing up, or looking away. The Sun is just too bright to look at. Every astronomy textbook I have ever read has an admonition against looking directly at the Sun, and it is common knowledge that looking at the Sun, even briefly, can cause permanent damage to your eyes.

While researching information on solar eye damage for this chapter, I stumbled across an amazing irony: while it is dangerous to view an eclipse with the unaided eye, it is actually far less dangerous to look at the Sun when it is not eclipsed! This may sound contradictory, but it actually is due to the mechanisms inside the eye that prevent overexposure from light.

There is copious evidence that little or no long-term damage results from observing the uneclipsed Sun. I was shocked to find this information; I have been steeped in a culture that says looking at the Sun with the unaided eye will result in permanent and total blindness. However, this is almost certainly not the case.

Andrew Young, an adjunct faculty member of the San Diego State University’s Department of Astronomy, has collected an astonishing amount of misinformation concerning solar blindness (see http://mintaka.sdsu.edu/GF/vision/Galileo.html). His research flies in the face of almost all common knowledge about solar blindness. He is quite strong in his statement: under normal circumstances, glancing at the Sun will not permanently damage your eyes.

“The eyes are just barely good enough at rejecting [damaging] light,” Young told me, because the pupil in the eye constricts dramatically when exposed to bright light, cutting off the vast majority of light entering the eye. Most people’s retinae don’t get overexposed when they glance at the Sun. Young quotes from a paper, “Chorioretinal Temperature Increases from Solar Observation,” published in the Bulletin of Mathematical Biophysics (vol. 33 [1971]: 1–17), in which the authors claim that under normal circumstances, the constriction of the eye’s pupil prevents too much light from the Sun from actually damaging the retina. There may be a slight (4 degrees Celsius) temperature rise in the tissue, but this is most likely not enough to cause permanent damage.

However, natural variations in the amount of pupil constriction between different people means that some might still be prone to retinal damage this way. These people make up the majority of solar retinopathy patients — people who suffer eye damage from looking at the Sun.

According to physicians at the Moorsfields Eye Hospital in London, England, observing the Sun can cause damage to the eye but not total blindness. On their web site [http://www.moorfields.org.uk/ef-solret.html], they report that half their patients with eye injury recover completely, only 10 percent suffer permanent vision loss, and, most interestingly, never has anyone had a total loss of vision from solar retinopathy.

So there is damage, and sometimes it can be severe, but most people recover, and no one has ever become totally blind by looking at the Sun. However, due to the natural variation in pupil constriction from person to person, I think I still need to stress that while it very well may be safe (or at least not very dangerous) to glance at the Sun, staring at it may still cause damage. The damage is most likely minimal, but why take chances? Try not to stare at the Sun, and try to minimize any glances at it. You might be part of the group that will suffer some injury from it.

So, if the full Sun is not likely to be dangerous, why should viewing a solar eclipse cause eye injury? During an eclipse most or all of the Sun is blocked by the Moon. However, think about what happens inside your eye when you view an eclipse. During a total eclipse the Sun’s surface is completely covered by the Moon, and the sky grows dark. When this happens, your pupil dilates; that is, it opens up wide. It does this to let in more light so you can see better in the dark.

The Moon completely blocks the Sun’s disk for a few minutes at most. Suddenly, when this phase of the eclipse ends, a small sliver of the Sun is revealed. Even though the total light from the Sun is less than when it is not being eclipsed, each part of the Sun is still producing just as much light. In other words, even if you block 99 percent of the Sun’s surface, that remaining 1 percent is still pretty bright — it’s 4,000 times brighter than the full Moon. An eclipse is not like a filter, blocking the light from hitting your eyes. Any piece of the Sun exposed will still focus this harmful light onto your retina, causing damage.

So when the Sun becomes visible again, with your pupil dilated wide, all that light gets in and hits your retina — and it’s then that sunlight can really and truly hurt your eye. The bluer light can cause a photochemical change in your retina, damaging it, although most likely not permanently. This effect, according to Young, is worse in children because as we age the lenses in our eyes turn yellowish. This blocks blue light, better protecting older retinae from the damage. However, children’s lenses are still clear, letting through the bad light. So while it’s dangerous to look