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

now.”

This will, of course, raise some protest, usually by a tenderfoot. “But the Sun is still up,” he’ll inevitably say. “You can’t see stars during the day!”

The older boy then puts on a condescending smile and says, “Of course I can. I just need to use my tube!” He then makes a tube out of rolled-up paper. Peering through it up at the sky, he’ll make some comment like, “Ah, there’s Orion now.” He’ll even invite other scouts (older boys, always) to take a look, and they all agree they can see some stars.

The young scout may resist for awhile, but, inevitably, curiosity will prevail. He’ll ask to take a look. The older scout hands him the tube, which he obligingly puts up to his eye… and another scout then pours his canteen down in the tube, drenching the young victim.

That victim would certainly have been me. A skeptic and a loudmouth through and through, I would have vehemently protested any attempt to see stars during the day. I would also have been a wet kid.

The thing is, I would have been a right wet kid. Looking at stars through a tube during the day won’t work. However, variations of this idea have been around a long time.

I’ve heard over and over again that it’s possible to see stars in the daytime from the bottom of a tall chimney or a deep well. I’ve never heard a decent explanation as to why this should work, although people make vague claims about the brightness of the sky being greatly diminished in a deep well, making it easier to see stars. The sky is so bright it washes out the stars, they reason. By cutting back on the amount of skylight, stars are easier to see.

This idea certainly sounds reasonable. It also has a long history. The Greek philosopher Aristotle mentions it in passing in one of his essays. No less an author than Charles Dickens also endorsed it in at least one of his works. In his 1837 book, The Pickwick Papers, he opens his twentieth chapter with this tortuous sentence:

In the ground-floor front of a dingy house, at the very farthest end of Freeman’s Court, Cornhill, sat the four clerks of Messrs. Dodson & Fogg, two of his Majesty’s attorneys of the courts of King’s Bench and Common Pleas at Westminster, and solicitors of the High Court of Chancery — the aforesaid clerks catching as favourable glimpses of heaven’s light and heaven’s sun, in the course of their daily labours, as a man might hope to do, were he placed at the bottom of a reasonably deep well; and without the opportunity of perceiving the stars in the day- time, which the latter secluded situation affords.

Still awake? In other words, the clerks could see stars as easily as someone at the bottom of a well. Evidently, Dickens’s publishers paid him by the word.

In a somewhat different version of this legend, Gregory of Tours, the sixth-century saint and historian, wrote in his Libri Miraculorum (“Book of Miracles”) that the Virgin Mary drew water from a well, which became blessed by her presence. Those who are pious enough can gaze into the water from this well and, if they cloak their heads with cloths to block out the light from the sky, they see the Star of Bethlehem reflected in it. This is a rather neat trick: if you can’t see it, you are not devout enough. Back to church with you!

The legend of seeing stars during the daytime is clearly tenacious, having been with us for a long chunk of our written history. I credit its longevity to the vague “scientificness” of the idea: as I pointed out before, it sounds like it might be true. Like eggs standing on end on the equinox, there is enough scientific jargon sprinkled in the legend that it bamboozles people. They don’t understand it, so it must be true. The long history also lends support to it, but anecdotes are not conclusive proof! For that we need to turn away from hearsay and look to science.

Let’s look closely at the legend: What is it about a chimney that might make it easier to see stars during the day? One obvious aspect is that it’s dark at the bottom of a chimney. As your eyes get adapted to the dark, they become more sensitive to light. Perhaps that helps you to see stars.

Unfortunately, it won’t work. Imagine you are sitting in the bottom of a tall chimney or smokestack, and it just so happens a star is directly overhead. Let’s also imagine you have let your eyes get dark-adapted. But think about it for a moment: if your eyes have adapted to the darkness, and you are more sensitive to light from the star, the darkness also makes you more sensitive to the light from the sky. It won’t be any easier to see a star. It’s like standing in a loud bar talking to a friend. It’s hard to hear him, so you use a hearing aid to increase your hearing sensitivity. But that won’t work. You’re focusing more sound in your ear from your friend, but you’re also increasing the sound you hear from the rest of the bar. Nothing really changes, and it’s just as hard to hear your friend.

Unfortunately, this also proves wrong the legend of seeing the Star of Bethlehem reflected from the water in a well. The water might reduce the brightness of the sky, but it reduces the brightness of the star by the exact same amount. You’d do better from the bottom of a chimney. That would change Nativity scenes extensively; a large smokestack next to the animals in the manger would take away a lot of the charm of Christmas.

You can see stars fairly easily at night, but not easily or at all during the day. The reason is just as obvious: at night, the sky is black and dark, but during the day it’s very bright. The sky is bright during the day basically because the Sun lights it up. (See chapter 4, “Blue Skies Smiling at Me,” for a more thorough explanation.)

The Sun isn’t the only source of light illuminating the sky. If you go out at night during a full Moon, only the brightest stars will be visible, struggling to overcome the glaring light from the Moon. City lights also brighten the sky. This is called light pollution, and it’s bad near cities, but it’s not a good thing even near small towns. That’s why astronomers try to build observatories far away from population centers.

During the day the bright sky swamps the rather meager light from the stars. As a matter of fact, on average the clear, daytime sky is roughly six million times brighter than that same patch of sky on a clear, moonless night. No wonder it’s so hard to see stars during the daytime! They have to fight a fierce amount of light from the sky itself.

Still, we know it’s possible to see the Moon, for example, during the day, so it’s possible for some astronomical objects to be bright enough to be seen against the daytime sky. How bright must a star be before we can see it against the sky?

The critical item here is contrast. To see an object against a bright background, the object must be bright enough for your eye to pick it out over the rest of the light coming from all around the object. Tests done early in the twentieth century showed that the eye can pick out a star against the sky background if the object is roughly 50 percent as bright as the background. It may seem weird, at first, that you can see something that’s fainter than the light around it. But the light from the star is concentrated in one spot, while the light from the sky is spread out all around it. The contrast with the sky is what makes the star visible.

Back in 1946, scientists performed experiments to see just how bright a star would need to be to poke out over the sky’s glow. They mimicked what a human would see during the day as opposed to at night by tuning the amount of background light around an artificial star. They found that the dimmest star that a person could see during the day was about five times brighter than Sirius, the brightest star in the sky (besides the Sun). In other words, even the brightest star in the sky is too faint to be seen during the day (Journal of the Optical Society of America 36, no. 8 [1946]: 480).

Therefore, it’s impossible for the unaided human eye to see any stars during the day. You’d think that’s the end of the story, but there’s still a twist to it. Those tests back in 1946 were done assuming the extra light was coming from the entire sky. If you are at the bottom of a chimney or a well, you aren’t seeing the whole sky, just a little piece of it. If you can block out most of the glare from the sky, you can see fainter stars.

Very early in the twentieth century, two astronomers separately tried to figure out the eye’s visibility limit, and to determine the faintest a star can be and still be seen against the night sky. They both found that by limiting the amount of sky they saw, they were able to greatly increase their ability to see faint stars. They determined that if you can cut out all but a tiny fraction of the sky, you can actually see stars that are about 10 times brighter than if seen in the whole sky — in which case it’s just possible to see Sirius during the day, but that’s it. The next brightest star, Canopus, is on the borderline of detectability. Let’s be generous and say that both stars can be seen this way. Let’s not forget, either, that there are bright planets visible to the naked eye: Mercury, Venus, Mars, and Jupiter can all appear brighter than Canopus or Sirius.

So we’ve determined that maybe, just maybe, we can just barely see six objects from a chimney, if the