Some 301 years ago, pioneering English astronomer Edmund Halley observed a solar eclipse and documented an unsettling phenomenon: a sudden, eerie shift in the weather.
He described the “chill and damp which attended the darkness,” noting that it evoked “a sense of horror” among his fellow spectators.
This mysterious “eclipse wind” puzzled Halley and others for centuries.
Now, thanks to groundbreaking research and the help of thousands of citizen scientists, we may finally have an answer.
What Happens When the Sun Goes Dark?
In 2015, during a partial solar eclipse in the UK, meteorologists from the University of Reading conducted the National Eclipse Weather Experiment (NEWEx), enlisting the aid of over 4,500 citizen scientists.
These volunteers meticulously recorded local weather data during the eclipse, providing researchers with a treasure trove of information.
The results were nothing short of fascinating: temperatures across the UK dropped by as much as 4°C (7.2°F) in some areas, while wind speeds slackened noticeably, dropping by up to 4 knots (7.4 km/h or 4.6 mph) in certain locations.
Atmospheric physicist Giles Harrison explained this phenomenon: “As the Sun disappears behind the Moon, the ground suddenly cools, just like at sunset.
This cooling halts the rising of warm air from the ground, which in turn slows down wind speeds and shifts their direction.”
The findings suggest that these changes are linked to Earth’s boundary layer—the thin layer of air near the ground that separates surface-level winds from those in the upper atmosphere.
This cooling effect during an eclipse disrupts the normal temperature gradients, leading to the observed drop in wind speed.
Challenging the Eclipse Myths
For centuries, eclipses have been shrouded in superstition and pseudoscience. Some early scientists even theorized the existence of “eclipse cyclones,” massive storms triggered by the celestial event.
However, the data from the 2015 experiment paints a far less dramatic picture.
While the cooling and wind changes are real, they are subtle—a far cry from the “horror” described by Halley.
Moreover, the cooling effect—averaging a 1°C (1.8°F) drop nationwide—may seem minor, but it provides critical insights into how Earth’s atmosphere responds to sudden changes in solar radiation.
As Sir Arnold Wolfendale, Astronomer Royal, put it:
“The heightened importance of climate change leads to great interest in a variety of climate parameters which can be studied when, uniquely, ‘the power is switched off.'”
What Makes Eclipse Winds Unique?
Unlike the gradual cooling of a typical sunset, an eclipse plunges an area into shadow almost instantly. This abrupt loss of sunlight creates a rapid cooling effect, which disrupts normal atmospheric behavior.
The boundary layer—normally warmed by the Sun—suddenly stabilizes as heat ceases to rise from the ground.
This stabilization slows the mixing of air near the surface, resulting in the observed drop in wind speeds.
Interestingly, the cooling effect during an eclipse also creates a noticeable shift in wind direction.
This shift occurs because of localized temperature gradients, which influence how air moves horizontally across the surface.
These subtle but significant changes in wind patterns have been observed in multiple eclipses, providing a consistent explanation for the long-debated “eclipse wind.”
Citizen Science: A Modern Renaissance
The success of the National Eclipse Weather Experiment underscores the power of citizen science. By engaging thousands of volunteers, researchers were able to gather real-time, large-scale data across the UK.
This collaborative effort mirrors the approach taken by Halley himself, who relied on amateur observers to document eclipses across Britain.
“We thank the thousands of fellow scientists around the country whose measurements contributed to this research,” Harrison said.
“Halley also relied on combining eclipse observations from amateur investigators. We have continued his approach.”
The findings from NEWEx were published in the prestigious Philosophical Transactions of the Royal Society A, marking a significant milestone in understanding eclipse-induced weather changes.
The experiment not only solved a centuries-old mystery but also highlighted the potential of crowdsourced scientific research.
The Next Great Eclipse
While the 2015 partial eclipse provided valuable insights, scientists are eager to validate their findings during future eclipses.
The next major opportunity will be a total solar eclipse visible across the US.
This event promises even more dramatic atmospheric effects, as the complete blockage of sunlight will create a larger temperature drop and potentially stronger wind changes.
If you’re planning to witness this rare celestial event, now is the time to book accommodations.
Interest is already sky-high, with hotels in prime viewing locations filling up fast.
Eclipse Winds and Climate Change
The study of eclipse winds offers more than just historical curiosity; it provides a unique lens through which to understand Earth’s climate system.
By observing how the atmosphere responds to sudden changes in solar radiation, scientists can refine models used to predict weather and climate patterns.
In an era of increasing concern about climate change, these insights are invaluable.
The ability to study “natural experiments” like eclipses allows researchers to test theories about atmospheric dynamics in real-world conditions.
As Harrison noted, “This research shows how even short-term changes in solar radiation can have measurable effects on our environment.”
A Legacy of Curiosity
From Halley’s 18th-century observations to modern-day experiments, the study of eclipse winds exemplifies humanity’s enduring curiosity about the natural world.
What began as a riddle has become a field of scientific inquiry, uniting amateur enthusiasts and professional researchers in the pursuit of knowledge.
As we look forward to future eclipses, one thing is certain: the next time the Sun disappears behind the Moon, we’ll be ready to measure, analyze, and marvel at the atmospheric changes it brings.
And in doing so, we continue a tradition of discovery that stretches back over three centuries.
