Weather Folklore
Red Sky at Night: The Science Behind the Sailor's Rhyme
"Red sky at night, sailor's delight; red sky in the morning, sailors take warning" is weather lore that often works in places where weather moves west to east, like the UK and most of the US. A red sunset means clear air to the west and fair weather coming; a red sunrise can mean the fair spell has passed and rain is approaching.
By the Weather Witch team · Updated October 4, 2026 · 6 min read
Key facts
- The red sky rhyme goes back to the Bible: in Matthew 16:2–3, Jesus says a red evening sky means fair weather and a red, lowering morning sky means foul weather.
- The Met Office says the saying is most reliable where weather systems mostly come from the west, as they do in the UK.
- Red skies appear when the low sun's light passes through a long stretch of atmosphere and dust and particles scatter away the blue light.
- Shakespeare used the warning version in Venus and Adonis (1593): a red morn betokens "wreck to the seaman, tempest to the field."
"Red sky at night, sailor's delight; red sky in the morning, sailors take warning" is one of the few pieces of weather lore that has real meteorology behind it. In places where weather usually moves from west to east, such as the UK and most of the United States, a red sunset tends to mean clear air and fair weather are heading your way, while a red sunrise can mean the fine spell has passed and rain is approaching. The Met Office calls the saying "most reliable when weather systems predominantly come from the west."
It is still a rule of thumb, not a forecast. This guide covers where the rhyme comes from, the physics that makes it work, when it fails, and a few other sky signs worth watching the evening before an outdoor wedding or event.
Where does "red sky at night" come from?
The red sky rhyme is at least 2,000 years old and first appears in writing in the Bible. In the Gospel of Matthew (16:2–3), Jesus answers people asking him for a sign from heaven. In the King James Version:
When it is evening, ye say, It will be fair weather: for the sky is red. And in the morning, It will be foul weather to day: for the sky is red and lowring.
His point was that people could read the sky but not the signs of the times. The weather part stuck.
By the late 16th century the warning version was common enough that Shakespeare could use it as a simile. In Venus and Adonis (1593) he compares something ominous to:
Like a red morn, that ever yet betoken'd Wreck to the seaman, tempest to the field, Sorrow to shepherds, woe unto the birds, Gusts and foul flaws to herdmen and to herds.
That one stanza explains why the rhyme has so many endings. In the UK you will mostly hear shepherd's delight; in the US and at sea it is sailor's delight, and the morning line becomes "shepherd's warning" or "sailors take warning."
Why does a red sky mean good weather? The science
A red sky at night means good weather because of two facts working together: how sunlight scatters, and which direction weather travels.
Why the sky turns red
At sunset and sunrise, sunlight reaches you at a low angle and passes through far more atmosphere than at noon. Along the way, air molecules and fine particles scatter the short blue wavelengths out of the beam, so mostly orange and red light gets through. According to the Met Office, a red sky is strongest when dust and small particles are trapped in the air by high pressure, the kind of pressure system that brings settled, dry weather.
Why direction matters
In the mid-latitudes, the prevailing winds blow from the west, so tomorrow's weather is usually somewhere to your west today. The sun sets in the west. Put those together:
| Sky | What you are seeing | What it often means |
|---|---|---|
| Red sky at night | The setting sun shining through clear, dusty, high-pressure air to the west and lighting up clouds overhead | The clear air is moving toward you: fair weather likely tomorrow |
| Red sky in the morning | The rising sun in the east lighting up clouds overhead and to the west | The high pressure has moved east; clouds of an approaching system may bring rain |
| Grey or dull sunset | Thick cloud or moisture to the west | Unsettled weather may be on the way |
| Clear, pale sunset | Clean, dry air without much dust | Usually fine, but no strong signal either way |
The Royal Meteorological Society reaches the same conclusion in its Met Matters piece on the rhyme: the saying "does stand up to scrutiny," with clear exceptions.
When does the red sky rhyme fail?
The red sky rhyme fails whenever its two assumptions break: that weather comes from the west, and that one system is not immediately followed by another.
- Weather from another direction. In the tropics, weather often travels east to west with the trade winds, so the logic flips or disappears. The same happens in the mid-latitudes when a blocking pattern or an easterly wind sets in.
- A second system right behind the first. A red sunrise can mean a system has just passed, and a red sunset can come in a short gap between two fronts.
- Summer thunderstorms. Afternoon storms build locally from heat and humidity, so a beautiful red sunset can still be followed by a stormy afternoon the next day.
- Smoke and haze. Wildfire smoke and pollution create spectacular red skies that have nothing to do with incoming weather.
- Mountains and coasts. Local winds, sea breezes and terrain can override the general westerly flow.
In short: a red sunset is a pleasant hint, a red sunrise is a reason to keep the umbrella handy, and neither replaces a forecast.
Other weather lore with some science behind it
Red sky is the most famous piece of weather lore, but sailors and farmers watched many other signs. These have at least partial support:
- "Ring around the moon, rain real soon." A halo around the moon is caused by ice crystals in thin, high cirrostratus cloud. That cloud often runs ahead of a warm front, so rain can follow within a day or so.
- "Mackerel sky and mares' tails make lofty ships carry low sails." Rippled, fish-scale clouds and wispy streaks high up can also mark an approaching front and rising wind.
- "When the dew is on the grass, rain will never come to pass." Heavy dew forms on clear, calm nights, which usually go with settled weather.
Many other customs are about wishing for good weather rather than predicting it, from eggs for St. Clare to the Japanese teru teru bozu doll. Our guide to weather superstitions for weddings collects them, and what a weather witch is traces the older history of people who claimed to command the sky.
What to watch the evening before an outdoor wedding
The evening before an outdoor wedding or event, a red sunset is a nice sign, but a few minutes with real tools will tell you much more.
- Look west at sunset. A clear, glowing horizon is encouraging. A wall of dark cloud to the west deserves a closer look at the forecast.
- Check the hourly forecast for your ceremony window, not the daily headline. Our guide to the rain forecast for your wedding explains how much to trust each time range.
- Check the radar in the morning for showers moving in from the west.
- Confirm your plan B with your planner, whatever the sky looks like.
Months before the day, the sky can't tell you anything, but history can. Our free wedding rain odds tool shows how often it has rained on your date at your venue over 30 years.
And if you want to send your own wish skyward, our personal wedding weather ritual is performed for your date and place in the nights before your day, with photo proof and a written blessing. Like watching the sunset, it is about hope and calm, not control; nothing can guarantee the weather. For do-it-yourself traditions, see how to stop rain, our collection of folk customs from around the world.
The bottom line
"Red sky at night, sailor's delight" is weather lore that often works: in the UK and most of the US, weather tends to come from the west, so a red sunset means clear air is heading your way, and a red sunrise can mean rain is coming behind it. The rhyme goes back to Matthew 16:2–3 and appears in Shakespeare. It fails in the tropics, with back-to-back fronts, summer thunderstorms and smoke. Enjoy the sunset the night before your big day, then check the hourly forecast before you trust it.
Frequently asked questions
Is red sky at night really a sign of good weather?
Often, yes, in the mid-latitudes. Most weather in the UK and much of the US moves from west to east. A red sunset means the sun is shining through clear, dusty air to the west, where tomorrow's weather is coming from. The Met Office says the saying is most reliable where weather comes from the west, but it is a rule of thumb, not a forecast.
What does a red sky in the morning mean?
A red sunrise means the rising sun in the east is lighting up clouds overhead or to the west. If those are the leading clouds of an approaching system, rain may follow later in the day. It is less reliable than the evening version, because one system can follow another quickly and not every red sunrise means storms.
Is it shepherd's delight or sailor's delight?
Both. Sailor's delight is the common version in the US and among people at sea, while shepherd's delight is more common in the UK. The rhyme has been adapted for many trades over the centuries. Shakespeare's version mentions seamen, fields, shepherds and herdsmen all at once.
Where does the saying red sky at night come from?
The oldest written form is in the Gospel of Matthew, chapter 16, verses 2 to 3, where Jesus notes that people say a red evening sky means fair weather and a red, lowering morning sky means foul weather. English versions appear in Shakespeare and in sailors' and farmers' lore from at least the 16th century.
Why is the sky red at sunset?
At sunset, sunlight travels through much more of the atmosphere to reach you. Air molecules and fine particles scatter the shorter blue wavelengths out of the beam, leaving reds and oranges. Dust and particles trapped under high pressure strengthen the effect, which is why a vivid sunset often goes with settled weather.