So is a red sky at night Shepard’s delight and red sky in the morning Shepard warning? Firstly to figure out this question we need to first explain why we have coloured skies. The answer to this was first given by a guy from Carlow named Tyndall. While also a brilliant scientist and supposed creator of the saying “Home Rule would be Rome Rule” he also had a fluffy beard. The reason the sky is blue is that light from the sun at shorter wavelengths is scattered more then longer wavelengths such as red. To put it another way.

If glass container of water that is rectangular in shape and shine a light through it on the shorter side the light will be blue. Shine it though the long side and the light will be red.This is the same as the earth at noon with the light overhead the blue light has been scattered down to you while the red light scattered away from you. In the evening the case s opposite. As it is noon over New York the blue is scattered down there (light is white directly from the sun the blue is just away from it) while here it is the red that is scattered to us.

The scatters in this situation are the molecules of Oxygen, Nitrogen, water and general dust in the Air. Now most storms in the Northern Hemisphere come west to East (prevailing winds and Jet stream)  So if the light is red in the evening this means that the air between the sun and us. Or for instance here and new york is highly scattering and full of particles of one form or another. This indicates high pressure and thus good weather.

Now a read sky in the morning means that the light coming from the East is suffering the same effects as the light from the West in the above paragraph the air is clear in the East which indicates that their is a low pressure coming in from the West. Very red indicates the atmosphere is very moist so bring an umbrella.

While it is fairly accurate at predicting approaching systems coming West to East any other direction it has no hope in predicting.