Copyright 2001, all rights reserved
You can't see stars in the daylight, even from a deep well or chimney
Q: 
Among my carpentry buddies there's a lunch time controversy going on over whether stars can be seen from a
deep well or canyon in the daytime. We in the 'yes' camp are confident we're right but don't have a clue why. Can
you fill us in--Tim M., Arcata, CA
A: Sorry, but I've got to take the other side. Daytime is just too bright for the stars to show up. Planets are a different matter. The brightness of the clear blue sky corresponds to about 100 bright stars per resolution element of your eye (1/60th of a degree). Since your eye can scan the entire sky, this amounts to a brightness equal to that of a billion bright stars shining in the sky.
[Corel] You can't see stars from tall chimneys in the daytime
Think about that: a brightness level equal to a billion bright stars. How do you distinguish one?
"A chimney would not be enough," says Andrew JS Hamilton, astrophysical and planetary sciences professor at the University of Colorado. "You'd have to look through a pinhole smaller than your eye can resolve. You'd have to be in a dark room or cave, excluding all scattered light except that coming through the pinhole. Then you'd have to look in exactly the right direction, exactly at a bright star, with no room for error."
Maybe with an exceedingly careful set up, you might see one. "But stars from the bottom of a canyon?" He says. "No way."
Planets, though, are brighter. "Under good conditions, Venus is easily visible to the unaided eye during the day as its brightness per eye resolution element is much higher than the sky (assuming there isn't much haze scattering sunlight)," says Robert Massey, astronomer at the Royal Observatory Greenwich, London, UK. "In this case, being down a well would help as the eye wouldn't be affected by the Sun's glare."
(Answered by April Holladay, science correspondent, September 12, 2001)
Further Surfing:
WonderQuest, USATODAY.com: Seeing planets