Why is a red sun at daybreak a sign of bad luck for sailors? Is there any truth to this superstition? Let's check what the meteorological sciences tell us.
Why does the sky change color?
Before we understand what a red sunrise means, we need to know why the sky changes color. White sunlight is actually a mixture of all the colors of the rainbow. It travels in waves, each color having its own wavelength.
When they enter the atmosphere, these waves will encounter molecules in the air, water droplets, dust, pollution, in short, obstacles.
The air molecules will better diffuse the shortest waves, that is to say the colors with dominant blue. On the other hand, the longer wavelengths, such as red, are very little diffused by these same air molecules.
Thus, the shades of the sky depend on the concentration of water vapor and dust in the sky.
The color red in the sky
In the morning and evening, the sun is low on the horizon. Its light must therefore pass through a layer of atmosphere ten to fifteen times greater to reach us than at the zenith.
The diffusion of waves will be more important on these large distances and favor the warm colors to the detriment of the short waves of blue. This is the reason why the sunrises and sunsets have tints of orange, pink and red.
What the colors say about the weather
" Morning rose, don't lend your cape to your neighbor ". The warm tones in the morning are the first signs of a low-pressure system and its rain trails, hence the recommendation of the saying to keep one's coat to shelter from the rain.
This is because dust tends to accumulate in the sky during high pressure events when the weather is good. As weather systems move from west to east, warm tones in the morning indicate that an area of high pressure and good weather is moving eastward, on the side where the sun rises. An area of lower pressure and poorer weather is then to the west, potentially bringing rain and wind with it.
The sailor is right to be wary of a too beautiful sunrise!
