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A debate about seeing stars or planet during the day below this answer to the Aviation SE question At what altitude might a pilot be able to see at least the brightest stars during the day? seems unresolved.

I'm pretty confident that Venus can be seen during the day through a cardboard tube only because I've seen this mentioned so many times.

But what about stars? And what's this about Aristotle and Sir John Herschel?

Here's a reprint of the debate referenced above just in case some get deleted in the future:

Yes, but the thing with the hole is a hoax, that doesn't work. What does work are binoculars.

Tell it to Aristotle and Sir John Herschel (see edit above).

The link does not confirm the ability to see stars from the bottom of a shaft, but rather refutes it.

Since they failed, even with binoculars, one wonders if sky conditions were less than optimal (a cirrus layer that isn't even readily visible would broaden the point of a star enough to make it invisible against the general scatter). Star visibility from the ground in daylight is well documented and repeatable, and doesn't require visual aids, if only the sky is completely clear.

uhoh
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    What would you accept as a "definitive answer?" Snopes? – Ohm's Lawman Aug 17 '20 at 01:33
  • @besmirched Thanks for that! It's a good starting point and I see both Mikkelson's names are on the page Snopes' creators, but if possible it would be good to track down the scientific works that are mentioned there and cite them directly. We could probably calculate sky brightness in magnitude per solid angle associated with visual acuity and compare that directly to a stars' brightness as well. – uhoh Aug 17 '20 at 02:15
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    FWIW, my eyes aren't great, but I've seen Venus during the daylight hours innumerable times, and not just near dusk or dawn. A few years ago, when it was very bright, and close to the crescent Moon, I managed to see it at least once every hour of the day. – PM 2Ring Aug 17 '20 at 03:05
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    FWIW I know of people who can and do point you to vega or sirius during day and direct you such that you can find them, too. You can see it. But once you lose eye contact with the star, you have to find it again. – planetmaker Aug 17 '20 at 06:06
  • @planetmaker Thanks for that! I'm pretty sure stars can be seen this way, and that a calculation based on this and a narrow tube will back this up. – uhoh Aug 17 '20 at 06:22
  • Paywalled (though other copies may exist): Koomen, M. J. 1959 Visibility of Stars at High Altitude in Daylight and also Smith, Alex J., 1952 Daylight Observation of Stars Also see Nat Geo. How Bright is the Daytime Sky? and maybe Human color vision and the unsaturated blue color of the daytime sky – uhoh Aug 17 '20 at 12:54
  • Who admit they are average persons, step forth. We need your judgement ! :-) –  Aug 17 '20 at 13:39
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    There is a discussion of seeing stars in daylight in Lord of the Rings at: https://scifi.stackexchange.com/questions/94922/how-can-tolkiens-characters-see-stars-during-the-daytime/95023#95023 And a discussion of te vision of Legolas at https://scifi.stackexchange.com/questions/76841/how-far-can-legolas-see/95028#95028 – M. A. Golding Aug 17 '20 at 16:13
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    Too see Venus during the day you don't need a tube. All you need is a reference to anchor your vision, like the top of a tree, or some other tall structure, which as seen by you is close to where Venus is visible in the sky. Without the anchor, the eye will just pass right by Venus because the contrast is so low. Once you have an anchor, the eye will have a reference point, and you'll find Venus again and again with ease. Sometimes. the crescent of the Moon can serve as an anchor, if Venus happens to be near the Moon. With an anchor, Venus is visible even at noon. – Florin Andrei Aug 17 '20 at 18:28
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    Re, Venus, Sirius, Vega, Eärendil, etc.; Lest we lose sight of the question, it was not asked whether there are other astronomical objects besides the Sun and the Moon that can be seen in the day-time sky. The question was, whether they can be seen better from the bottom of a well. – Ohm's Lawman Aug 17 '20 at 21:39

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This article (Hughes 1983, "On Seeing Stars (especially up chimneys") from the Quarterly Journal of the Royal Astronomical Society seems like a pretty good account of the "phenomenon", including both classical and literary claims (e.g., in stories by Dickens and Kipling) and actual experiments. It appears that the Aristotle reference ("people in pits and wells sometimes see stars", from Generation of Animals) is not an eyewitness report by Aristotle himself -- and, given that Aristotle claimed men had more teeth than women, one should always be a bit skeptical about his claims; there is also the possibility that these were sightings of planets, which can sometimes be seen in the daytime. The Herschel reference is to an "optician" Herschel knew who claimed to have seen a star this way once or twice, not something Herschel himself verified.

In Section 2 of the article there are discussions of actual serious (and unsuccessful) attempts to test this, including numerous attempts by Alexander von Humboldt and well-described attempts by astronomers like J. Allen Hynek, who tried (with "several members of my astronomy class") to observe Vega from the bottom of an abandoned smokestack, and some measurements taken at the botton of a tall chimney which verified that the brightness of the sky was unchanged from that seen outside.

There are also some discussions of the sensitivity of the human eye. The conclusion I get from this is that it is barely possible that someone with good eyes and an extremely restricted field of view (much smaller than "from the bottom of a well" or a "cardboard tube") might be able to make out Sirius, but probably nothing fainter.

Edited to add: This article (Können et al. 2015) reports a daytime sighting of Sirius from the La Palma observatory. They note that there were able to do this because they had pointed their telescope at Sirius, and looked along the finder scope (knowing the offset), so they knew exactly where to look. (Even then, it was difficult: "Both of them saw Sirius, but it was difficult; as Wallis put it during his attempt: 'It comes and it goes.'") Knowing exactly where to look is important, because

the limiting magnitude of photopic vision decreases linearly and rapidly with distance from the center of field of the human eye: at 2° from the center the limiting magnitude has worsened by 1 magnitude; at 4° by 2 magnitudes [16]. This means that for an unintentional sighting, a star should be roughly 2 magnitudes brighter than the limiting magnitude. Venus meets this requirement, but for Sirius there is little hope for an unprepared sighting.

(Short answer: Generally speaking, you cannot see stars from the bottom of a well, chimney, mining pit, etc., during the daytime. And you certainly aren't going to see multiple stars from the bottom of a canyon, even if there's a lovely evocation of that idea at one point in The Lord of the Rings.)

Peter Erwin
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  • Wow what an entertaining and thoroughly researched answer, thank you! I'm gratified to see that you even tracked down the reference to Herschel. – uhoh Aug 17 '20 at 16:01
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    And there is a discussion of the visibility of stars in Lord of The Rings at: https://scifi.stackexchange.com/questions/94922/how-can-tolkiens-characters-see-stars-during-the-daytime/95023#95023 – M. A. Golding Aug 17 '20 at 16:08