The sky... again

[Pootle]

How high do you have to go before it starts getting dark, assuming its midday?

[ugly_bob]

It won't. It only gets dark because you are on the opposite side of the earth to the sun. So if it's light on the ground, it will be in the sky too.

[Pootle]

But doesn't the sky slowly go from light blue to dark blue to black?

[JudgeJ]

The sky looks bright and blue because the sunlight is diffused by the atmosphere. It�s rather like shining a torch through a sheet of paper. The torch tends to illuminate all of the paper, even though the it provides a more concentrated light source.

The sky looks black from the moon because the moon has no atmosphere. Similarly astronauts orbiting the earth at 200 miles see a black sky because the atmosphere is beneath them.

I don�t know the precise answer to your question but I should think that once above about twenty five miles, the atmosphere is very thin (most of it will be below you at that height) and the sky would begin to lose its colour and brilliance.