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In this comment I pondered if I should ask:

"Did Test pilot and astronaut Joseph A. Walker see stars during the day when flying the X-15 above the Karman line?

But instead, I'll just ask at what altitude might a pilot be able to see at least the brightest stars during the day?

Assume cockpit lights and panel illumination are dim-able and a high tech high altitude aircraft (e.g. the X-15 or something modern or near-future) is used.

I don't think it's easy to see bright stars during the day at cruise altitude by eye without some help, but at some altitude it should be.

Is there any information on what altitude this might be?

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    $\begingroup$ Venus is visible from the ground during the day if you know exactly where to look. You might have to be more specific about which stars, and how "visible" they have to be to qualify. $\endgroup$
    – Dave-CFII
    Jan 2 '20 at 1:23
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    $\begingroup$ @Dave-CFII it's difficult to pre-specify without being in danger of excluding an otherwise helpful answer. I'm guessing that commercial pilots don't regularly see stars during the day, and while a cardboard tube and some google can help people see Venus during the day, it wouldn't count as a star. Unfortunately the Sun does count; hopefully nobody will post that as an answer. $\endgroup$
    – uhoh
    Jan 2 '20 at 1:28
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    $\begingroup$ If you don't get a good answer here, you could try astronomy.SE $\endgroup$
    – Pondlife
    Jan 2 '20 at 3:01
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    $\begingroup$ I see a very bright star every day during the day with naked eye at altitude 0 :-) $\endgroup$
    – Déjà vu
    Jan 3 '20 at 16:57
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SR-71 pilots saw the stars, but of course there is no account of the exact height, they started to see them. They were flying around at 80000 feet at some point in their mission profile. Basically you have to get above most of the atmosphere. So you should start to see stars above 43000 feet. Of course there are some other options, you see them during an eclipse or above the Arctic circles in the right season. You can always see the stars, if you know where to look and if you have a telescope, but I presume you mean to see them with the naked eye?

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    $\begingroup$ I've not heard any reports of seeing stars during the day from Concorde at 60,000ft, so that narrows it down a bit. $\endgroup$ Jan 2 '20 at 10:40
  • $\begingroup$ Well the height of the troposphere varies with season and latitude. Also the concorde has very small windows. I should also say that this is a guesstimate. The troposphere scatters most of the light or rather the water vapor. $\endgroup$
    – mike
    Jan 2 '20 at 10:49
  • $\begingroup$ @bogl perhaps mike was typing on a telephone at the time $\endgroup$
    – uhoh
    Jan 2 '20 at 11:57
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    $\begingroup$ Yes! Telescope! Although I can see at least one star on my telephone too! 🤪 $\endgroup$
    – mike
    Jan 2 '20 at 12:22
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    $\begingroup$ @mike hehe, not being rude/serious or anything but are jokes allowed in comments?, cause I have one on my mind on another answer and it’s really good. $\endgroup$
    – Valay_17
    Jan 3 '20 at 15:42
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Venus (not a star, but often mentioned in this context), Arcturus, Vega, Rigel, Sirius, and several other very bright stars are visible in daylight from sea level when sky conditions are right -- if you know exactly where to look.

Random stars are reportedly visible from within a deep enough hole (a well or mine shaft, for instance), because the bright scattered light of the general sky is mostly blocked by earth or rock and the eyes are adapted to the dimmer light.

So, to answer the question, in the limit, below ground level (though you're unlikely to fly there), or at sea level under the right conditions.

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    $\begingroup$ Yes, but the thing with the hole is a hoax, that doesn't work. What does work are binoculars. $\endgroup$
    – mike
    Jan 2 '20 at 12:21
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    $\begingroup$ Tell it to Aristotle and Sir John Herschel (see edit above). $\endgroup$
    – Zeiss Ikon
    Jan 2 '20 at 12:52
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    $\begingroup$ The link does not confirm the ability to see stars from the bottom of a shaft, but rather refutes it. $\endgroup$ Jan 2 '20 at 12:58
  • $\begingroup$ 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. $\endgroup$
    – Zeiss Ikon
    Jan 2 '20 at 14:32
  • $\begingroup$ @ZeissIkon I've just asked Can an average person see stars from the bottom of a well or through cardboard tubes? Definitive answer required! $\endgroup$
    – uhoh
    Aug 17 '20 at 0:25

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