This saying dates back centuries and the thinking behind it is simple: you can’t see stars in the day because the sun is too bright, but at the bottom of a well or chimney almost all of this sunlight is blocked out, reducing the brightness of the sky so the stars become visible. Right?
Sadly not. No matter how far you have fallen, the sky will always be blue in the daytime. If it were possible to see the stars in the daylight, then no doubt astronomers would be lurking at the bottom of wells, telescopes in hand. Instead, you only find batman and fairy tale frogs down there.
To understand why you can’t see the stars, even if you are shielded from the sun, you need to understand why the sky looks blue in the first place.
(see ‘Why is the sky red before a storm?’). And as anyone who’s ever seen a rainbow (or one of those rainbow-prism experiments) will know, the sun’s white light is a actually combination of the whole spectrum of colours. When the sun’s light strikes the gas particles in the atmosphere, a phenomenon called ‘scattering’ occurs – nitrogen and oxygen in our atmosphere cause the blue light to be ‘scattered’ out in all directions. And as this blue light is far brighter than the stars, they are hidden from our view.
(Interestingly, on other planets with different atmospheres, other colours may be scattered, giving the sky a different colour. For example, Mars has a red sky and some parts of Saturn have a yellow sky.)
The only celestial body that you can reliably see in the daytime is the planet Venus, which looks like a very bright star. But because Venus appears low in the sky, you certainly won’t be able to spot that from the bottom of a well.
And in actual fact, rather than block out stray light rays to dim the sky, the contrast between the blue light above and the darkness at the bottom of the well/chimney actually makes the sky appear brighter than it normally would.
If you still don’t believe the science, then clamber down and give it a try regardless. And while you’re there, keep your ears open for creatures that go ‘ribbit’. Why not give one a kiss? I hear that it might turn into an astronomer.
Answer by Dr. Stu
Image credit: Samuele Ghilardi on flickr