Expert: Philip Stahl - 1/8/2008

Question
As we were sitting at work this afternoon, we watched the sunset. Why does it look like the sun pauses as it's going down? one person said it was our eyes playing tricks but 2 of us saw it.

Answer
Hello,

At sunrise and sunset, the Sun's rays (light) must travel through much thicker layers of the atmosphere, which may also contain more dust. (Atmospheric thickness vertically upwards is much much less than horizontally).

As the rays travel much greater thicknesses of atmosphere, and scatter more from the dust particles encountered, the light is refracted more toward longer wavelength (red) regions of the spectrum.

Refraction will also cause displacements of position in the object (Sun) that may indeed play "tricks" on the unwary. Of course, one such trick is that when you observe the Sun just on the horizon, it has in fact actually *set* and is *below* the horizon. The tiny degree or differential can actually be worked out.

So, I suspect that as you observed the Sun apparently move to the horizon (through increasing layers of atmosphere) you may well have seen what you interpreted as a "pause" - but which was, in fact, atmospheric refraction having its way with your eyes.