We can see objects in the sky during a clear day, but only to a point, after which the thickness of our atmosphere blocks our view of the cosmos - that is to say, we see blue. At what distance from the naked eye does the clear blue sky become so opaque?

krazykritik

It varies. Scientists aren't even completely sure as to why we even see the colour blue in our sky, but following are two of the main reasons why scientists believe that the colour blue is the colour we see in the sky. The 'blue' we see has been "rumored" to be caused by ozone, which is present in the bottom two of the five layers of earth's atmosphere. The first layer is called the troposphere and the layer above it is called the stratosphere. When enough ozone molecules are present, they form a pale blue gas. It also has been thought that the sun's rays scatter the blue light much more than red light and that the cooler the temperature, the more that blue light gets scattered. This could be why we see much more red and orange light around sunset time. As far as seeing the color blue disappear when night comes on, it is because the lack of the sun's rays means that the blue color is no longer being affected and scattered by the sunbeams so we only see the dark black of the sky. The troposphere(earth's first atmospheric layer), is approximately 16kms thick(10 miles). After the troposphere, the second atmospheric layer, the stratosphere, measures from approximately 16kms to 48kms(10 - 30 miles). The troposphere contains about 10% of earth's ozone, while the stratosphere contains the other 90%. The third layer, the mesosphere, begins where the stratosphere ends(about 48kms(30 miles) above the earth, and contains very little ozone, less than 1/10th of 1%. So, if we go with the explanations about ozone being blue, then we can say that it is at the altitude of the top of the stratosphere when the blue 'disappears'. The "minimum" distance measurement requested in your question would therefore be approximately 50kms when the sky turns dark. If we go with the explanation that the sun shining through the air gives us the blue colour of our sky, then we have to consider the next three layers of earth's atmosphere, the mesosphere, the thermosphere, and the exosphere(also known as the ionosphere). The last layer, the exosphere, starts at approximately 500kms and is about 10-25kms in thickness. o if that's the theory we're using, then the answer to your question is that the "opaque" effect occurs at 500-525kms above the earth's surface, or from the point of the "naked eye". Remember, these are still "theories" so this, by no means, is to be considered "scientifically accurate". I hope you enjoyed reading the response! Mike the krazykritik Feb 20 10, 1:00 AM