I read somewhere, probably in a Time-Life book when I was a kid, that the Great Pyramid had a long narrow shaft which was aligned with the pole star. Supposedly at the time the Pyramid was built, you could see this star, even in the daytime, if you were at the bottom of the shaft.
Is this possible?
I believe that at the time of the Pyramids, the pole star was Thuban, but someone can correct me. This is not a terribly bright star, so my money’s on not even close. Maybe the people at the bottom of the shaft just mistook daylight for a star?
There’s a whole discussion on whether or not you can see stars in the daytime if you stand at the bottom of a shaft. You can find a lot of the references in Jeral Waler’s The Flying Circus of Physics. IIRC, the upshot was that this was all a myth – standing at the bottom of a well or shaft doesn’t help you see stars in the daytime any better than standing in the open.
Do you happen to remember what the physical arguments for this phenomenon are? It doesn’t seem to me that there’d be any.
IIRC (My books on this are at home) the idea that you could see stars in the daytime if you stood at the bottom of a shaft or well go back to Aristotle, so the original case wasn’t argued on modern physical merits. A lot of people since have claimed the same thing to be true, however, apparently without checking it out. The train of thought seems to be that if you are at the bottom of a long tube you exclude scattered light from the rest of the sky, which somehow makes the star easier to see. It doesn’t change the amplitude of the scattering in the same patch of sky where the star is, however, which is the important thing. My understanding is that the Rayleigh scattered (and minor multiple scattered) sunlight “swamps” the light from the star, so you can’t distinguish the star against that large background level.
The papers cited by Walker – I’ve looked them up – argue on both theoretical grounds and experimental grounds (someone went into a hole and the ground and looked for stars that he should have been able to see. He couldn’t).
A few years ago, however, I brought this up with someone who did a lot of work for the military, and declared, on the basis of this, that you couldn’t see stars in the daytime. He said that I was wrong – with the proper equipment, he said, you could. You, Achernar, are probably in a better position to answer that than I am.
You can see Venus during the day. I’ve done it. You have to know exactly where to look, and it helps to use binoculars or a telescope for the first sighting, but once you’ve nailed down the location you can see it with the naked eye.
You have to stand in the shade to do this, or the glare from the sun will wash everything out. Standing in a well isn’t necessary, and it wouldn’t particularly help.
I have also read, although I have never verified it, that under good conditions you can spot other bright objects like Jupiter and Sirius a couple of minutes before sunset.
That’s the extent of daytime star and planet viewing possible in our atmosphere. No pole star is or has been anywhere near bright enough to see during the day, from a well or otherwise, at any time in human history.
I must say that, without having tried the experiment, I do not see any reason why the scattering of that one patch of sky is any less because you at the bottom of a long tube. It wouldn’t surprise me if someone said you could see a few of the brightest stars from the top of Everest, with or without a tunnell.
I once followed Venus walking to work for an hour and a half. It is in late October (the week before daylight saving ended) and I picked it before dawn at around 6:45 and was able to follow it till I got to my office at 8:15. I have the impression that if you know where to look, then in most phases Venus is visible in the day so long as it is sufficiently high in the sky. But Venus can be at least 3 magnitudes brigher than any star (except the sun) and you still had to know exactly where to look. I did see a very odd optical illusion. A very light cloud passed in front for a few minutes and since Venus was still visible, it gave the inescapable impression that it was in front of the cloud and moving. Obviously, the sky was exceptionally clear that morning.
Check this thread over at Bad Astronomy: Apparent magnitude of the sky
The scattered sunlight from the sky is linearly polarized 90 degrees away from the Sun. If you look at the sky wearing polarized sunglasses, you’ll notice a dark stripe across the sky. Perhaps if you’re in a hole, wearing polarized sunglasses, and there happens to be a bright star there…