The Saharan dust plumes can make the sky red. Are they the source of the old saying "Red skies at night, sailor's delight. Red skies in the morning, sailor take warning"?
My investigation into the phrase “red skies at night, sailor’s delight” started with this question from Thomas last week:
Hi, Mignon. My name is Thomas, from Indianapolis, and I've been reading about the Sahara dust plume that's heading for U.S. on the tradewinds, and I read that supposedly it is going to cause a whole bunch of fantastic sunsets, and also that when the Sahara dust gets in the atmosphere, it suppresses the formation of tropical storms and hurricanes. And I was wondering if that might be the origin to the old saying “red sky at night, sailor’s delight” and if not, do you know where that comes from or what it dates to? Thanks so much, I love the podcast.
It’s a great question, Thomas.
The massive Saharan dust plume you were asking about has now reached some southern parts of the United States, and it’s mostly gone, but a smaller second plume is on its way.
These plumes aren’t a new phenomenon—they happen all the time when wind blows across the huge deserts in North Africa, and they aren’t just limited to the U.S. either, the dust also makes it to parts of Europe—but according to National Geographic, the plume that wafted over regions from Puerto Rico to Texas last week was the biggest plume since people started recording the size by satellite in 1979.
Since they aren’t new, it’s a reasonable question to wonder if they are the source of the saying “Red skies at night, sailor’s delight. Red skies in the morning, sailor take warning,” but I don’t think so. I believe that regular weather is more likely to be the source because even though the dust storms are common, clouds also cause red skies, and they are much more common.
The ‘Red Skies” Saying Is Old
The concept of red skies at night being a harbinger of good weather is old. For example, the wonderful site “The Phrase Finder” traces written mentions back to one of my favorite old sources, the Wyclif bible, published in 1395.
And at least in England, where the concept and phrase originated, red skies are actually quite predictive of the weather. They may not rival modern weather prediction, but in the 1300s, they were useful. It works because most storms in the U.K. come from the west.
Why Red Light Means Clouds
Clouds reflect all the colors of light from the sun, but because of the way different colors of light travel through the atmosphere, red light is much better at reaching distant clouds than the other colors. So clouds end up reflecting a lot of red light, especially early and late in the day because that’s when the light has to travel the farthest through the atmosphere to reach the clouds, so as it’s making its way through all that atmosphere, the other colors of light are getting filtered out, and the red light is just powering through. You can think of clouds at sunrise and sunset as red light reflectors.
So if you’re in the U.K. and you’re seeing a red sky at night, it means the clouds have already passed you by. They’re east of you, reflecting red light back from the setting sun in the west. You don’t have to worry about approaching storms. Storms come from the west, and the west is clear.
But if you see a red sky in the morning, it means clouds are to the west, probably heading toward you, because they’re reflecting red light from the sun rising in the east. You may not be able to see those western clouds that are heading toward you because of the curvature of the earth, but the red light tells you they’re out there doing their reflective thing.
Red Skies at Night, Shepherd’s Delight
And here’s an interesting final note: I’ve only heard the version as “red skies at night, sailor’s delight,” but multiple sources also say that there’s a now less common version, that may have been the first version, that says “red skies at night, shepherd’s delight,” presumably because shepherds cared a lot about the weather too. For example, in Shakespeare’s “Venus & Adonis,” Shakespeare wrote about a “red morn” bringing sorrow to both seamen and shepherds.
So that’s the origin of the “red skies at night, sailor’s delight” saying. It actually does a decent job of predicting the weather in some parts of the world because of the way clouds reflect red light in the atmosphere.
Thanks for the question, Thomas.
Image courtesy of Shutterstock.