Hump to the west: weather proverbs and omens of the Moon
From the hump to the west to Luna mendax, from lunar haloes to the colour of the disc: weather proverbs about the Moon and their roots in Aratus and Virgil.
Before weather forecasts, farmers, shepherds and sailors read the weather in the sky. The Moon, with her colour, her haloes and the position of her horns, was one of the most closely watched signs. From this age-old experience came proverbs still repeated today, some useful for recognising the lunar phases, others tied to weather omens. Their origin lies partly in ancient literature, from Aratus to Virgil.
Recognising the phases
The best-known proverb in Italy distinguishes the waxing Moon from the waning one: «Hump to the west, the Moon is waxing; hump to the east, the Moon is waning». In the northern hemisphere the lit part of the waxing Moon faces west, towards the setting Sun, while the waning Moon shows her hump to the east. It is a correct observation, turning an astronomical phenomenon into a formula easy to remember even for children.
In Latin there circulated a similar saying with the opposite sense: Luna mendax, «the Moon is a liar». The waxing crescent, in fact, has the shape of a D, the initial of decrescere, «to decrease», while the waning crescent recalls a C, the initial of crescere, «to grow». The Moon thus seems to say the opposite of what she does. The game works only in languages using those initials and in the northern hemisphere, but it enjoyed long success in schools and calendars.
Colours and haloes
Many proverbs link the colour of the Moon to the weather of the following days. A widely known Latin adage sums up the idea in a few words: Luna pallida pluit, rubicunda flat, alba serenat, that is, a pale Moon brings rain, a reddish one wind, a white and clear one fair weather. The idea springs from observation, since the colour and sharpness of the disc depend on moisture and dust in the atmosphere, but it guarantees no certain forecast.
Haloes, luminous rings that form around the Moon when her light passes through thin veils of high cloud made of ice crystals, were traditionally regarded as heralds of rain. These veils often precede the arrival of a weather front, and so the omen contains an element of empirical truth. In many regions proverbs about the lunar halo circulate, with local variants that make its meaning depend on the width of the ring or on the moment it appears.
From Aratus to Virgil
Lunar weather signs were already codified in Greek antiquity. Aratus of Soli, in the third century BC, devoted part of his Phaenomena to weather omens, observing the shape of the Moon's horns in the first days of the month, their colour and their sharpness. A treatise on weather signs, attributed to Theophrastus but perhaps the work of his school, gathers similar observations. Aratus became widely known in Latin through the translations of Cicero and Germanicus.
Virgil took up these themes in the first book of the Georgics, published around 29 BC, where he describes the signs of the new moon: if her horns enclose a dark air, much rain is foretold; if her face is tinged with a maidenly blush, wind will come; if on the fourth day she is clear, the rest of the month will be fair. These lines, commented on in schools for centuries, fixed in European memory the link between the Moon and the weather.
Lunar weather proverbs belong to a body of observational knowledge that meteorology has surpassed with far more precise instruments. Yet they remain precious as linguistic and cultural heritage, because they preserve the attention to the sky of generations of people who depended on reading it for their harvests, for navigation and for the safety of their journeys.