Citizen Scientists Help Crack 300 Year Old Mystery Of Eclipse Wind

Being able to witness a solar eclipse is certainly a distinct experience. Even though the spectacle is mostly visual, there can be other effects as well. The air can cool, and observers may notice a decrease in wind speed or a change in wind direction. There might even be an eerie silence.

Experiences like this have been noted for centuries, and famed astronomer Edmund Halley wrote of the ‘Chill and Damp which attended the Darkness’ during an eclipse in 1715, which he noted caused ‘some sense of Horror’ among those who were witnessing the event.

While most people would describe an eclipse as ‘awe-inspiring’ (and not horrifying at all) the atmospheric changes noted by observers over the years has been called the “eclipse wind.” And now, based on the observations of over 4,500 citizen scientists in the UK during the partial eclipse on March 20, 2015, this effect is not just a figment of anyone’s imagination; it is a real phenomenon.

Partial phases of the solar eclipse on March 20, 2015 as seen from the United Kingdom. Credit and copyright: Sarah and Simon Fisher.
Partial phases of the solar eclipse today as seen from the United Kingdom. Credit and copyright: Sarah and Simon Fisher.

The National Eclipse Weather Experiment (NEWEx) was a UK-wide citizen science project for collecting atmospheric data during that eclipse. Members of the public – including about 200 schools – recorded weather changes such as air temperature, wind speed, wind direction and cloud cover every five minutes during the eclipse. That data, submitted online, was compared with official data from the UK’s Met office observations, the United Kingdom’s national weather service.

“The NEWEx was, as far as we know, a world first, in measuring and analyzing eclipse changes in the weather on a national scale, in close to real time, through engagement of a network of citizen scientists,” wrote researchers Luke Barnard, Giles Harrison, Suzanne Gray and Antonio Portas from the University of Reading, in one of a series of new papers about eclipse meteorology published this week.

The data revealed that not only did the atmosphere cool during the eclipse – which is not surprising since solar radiation is being blocked by the Moon – but the winds and cloud cover also decreased. The cumulative effect is real, not just anecdotal, the team said.

The Data

NEWEx collected 15,606 meteorological observations from 309 locations within the UK and from those observations the science team was able to derive estimates of the near-surface air temperature, cloudiness and near-surface wind speed fields across many UK sites. The data submitted by citizen scientists were combined with Met Office surface weather stations and a network of roadside weather sensors that monitor highway conditions. The combination of data helped unravel the centuries-old mystery of the eclipse wind.

Geographical distribution of participants in the NEWEx citizen science project during the March 20, 2015 solar eclipse in the UK, with designations between schools (yellow squares) and non-schools (pink dots). Credit: Antonio M. Portas, Luke Barnard, Chris Scott, R. Giles Harrison.
Geographical distribution of participants in the NEWEx citizen science project during the March 20, 2015 solar eclipse in the UK, with designations between schools (yellow squares) and non-schools (pink dots). Credit: Antonio M. Portas, Luke Barnard, Chris Scott, R. Giles Harrison.
From analysis of the data, they found that the wind change is caused by variations to the “boundary layer” – the area of air that usually separates high-level winds from those at the ground.

“There have been lots of theories about the eclipse wind over the years, but we think this is the most compelling explanation yet,” said Harrison in a press release from the University of Reading in the UK. “As the sun disappears behind the moon the ground suddenly cools, just like at sunset. This means warm air stops rising from the ground, causing a drop in wind speed and a shift in its direction, as the slowing of the air by the Earth’s surface changes.”

The measurements from citizen scientists clearly showed temperature drops and a decrease in clouds. The team did note that because of the low velocity of winds and some areas where cloud cover change was small, it was difficult for the participants to make some of the measurements. But the high level of participation across the UK provided enough data for the team to make their conclusions.

“Halley also relied on combining eclipse observations from amateur investigators across Britain. We have continued his approach,” Harrison said.

A total of 16 new papers and reports were published this week in a special ‘eclipse meteorology’ issue of the world’s oldest scientific journal, Philosophical Transactions of the Royal Society A. The special issue is published 301 years after Halley’s report of the eclipse in London in 1715 – and in exactly the same journal.

The team wrote that they hope a similar citizen science effort might take place in August 2017, when a total solar eclipse will be visible from North America, providing another opportunity to study eclipse-induced meteorology changes.
“NEWEx serves as a useful example of the strengths and challenges of using a citizen science approach to study eclipse-induced meteorological changes, and could provide a template for a similar study for the August 2017 eclipse,” the team said.

Sources: Paper: The National Eclipse Weather Experiment: an assessment of citizen scientist weather observations, Philosophical Transactions of the Royal Society A, University of Reading.

Kicking Off Eclipse Season: Our Guide to the September 13th Partial Solar Eclipse

Eclipse season 2 of 2 for 2015 is nigh this weekend, book-ended by a partial solar eclipse on September 13th, and a total lunar eclipse on September 28th.

First, the bad news. This weekend’s partial solar eclipse only touches down across the very southern tip of the African continent, Madagascar, a few remote stations in Antarctica, and a few wind-swept islands in the southern Indian Ocean.  More than likely, the only views afforded humanity by Sunday’s partial solar eclipse will come out of South Africa, where the eclipse will be about 40% partial around 5:30 Universal Time (UT).

Image credit:
An animation of the September 13th eclipse. Image credit: NASA/GSFC/A.T. Sinclair

It’s the curious circumstances surrounding the September 13th eclipse that conspire to hide it from the majority of humanity. First, the Moon reaches its ascending node along the plane of the ecliptic at 4:38 UT on Monday, September 14th, nearly 22 hours after New phase. The umbra, or dark inner core of the shadow of Earth’s Moon ‘misses’ the Earth, passing about 380 kilometres or 230 miles above the South Pole. The outer penumbra of the Moon’s shadow just brushes the planet Earth, assuring a 79% maximum obscuration of the Sun over Antarctica around 6:55 UT.

Second, the Moon also reaches its most distant apogee for 2015 on September 14th at 11:29 UT, 406,465 kilometers from the Earth. This is just over 28 hours after New, assuring that the umbra of the Moon falls 25,000 kilometres short of striking the Earth. The eclipse would be an annular one, even if we were in line to see it.

Image Credit:
The footprint of Sunday’s eclipse. Image Credit: Michael Zeiler/TheGreatAmericanEclipse.com

Observers will see the eclipse begin at sunrise over South Africa and the Kalahari Desert, great for photography and catching the eclipse along with foreground objects. Observers will need to follow solar observing safety protocols during all stages of the eclipse. A high value neutral density filter will bring out the silhouette of foreground objects while preserving the image of the partially eclipsed Sun, but remember that such a filter is for photographic use only.

Image credit:
Maximum obscuration of the Sun, with times and solar elevation for four selected sites. Image credit: Stellarium

P1, or the first contact of the Moon’s penumbra with the Earth occurs on the morning of the 13th over the Angola/South Africa border at 4:41 UT, and the shadow footprint races across the southern Indian Ocean to depart Earth near the Antarctic coast (P4) at 09:06 UT.

New Moon occurs on September 13th at 6:43 UT, marking the start of lunation 1147.

Image credit:
A close-up of the eclipse circumstances for southern Africa. Image credit: Michael Zeiler/TheGreatAmericanEclipse.com

For saros buffs, this eclipse is a part of saros series 125 (member 54 of 73). Saros 125 started on February 4th, 1060 and produced just four total eclipses in the late 13th and early 14th centuries. Mark your calendars, as this saros will end with a brief partial eclipse on April 8th, 2358. The final total eclipse for this particular saros crossed over central Europe on July 16th, 1330, when an observation by monks near Prague noted “the Sun was so greatly obscured that of its great body, only a small extremity like a three night old Moon was seen.”

Image credit: Dave Dickinson
A partially eclipsed Sun rising over the Vehicle Assembly Building at the Kennedy Space Center. Image credit: Dave Dickinson

Missing out on the eclipse? The good folks over at Slooh have got you covered, with a live webcast set to start at 4:30 UT/12:30 AM EDT.

Planning an ad-hoc webcast of your own from the eclipse viewing zone? Let us know!

There are also some chances to nab the eclipse from space via solar observing satellites in low Earth orbit:

The European Space Agency’s Proba-2 will see eclipses on the following passes – 5:01 UT (partial)/6:31 UT (annular) 8:00 UT (partial).

Image credit:
The view from ESA’s Proba-2 spacecraft at 6:31 UT. Image credit: Starry Night Education Software

And JAXA’s Hinode mission will see the same at the following times: 5:56 UT (Partial)/7:46 UT (partial). Unfortunately, there are no good circumstances for an ISS transit this time around, as the ISS never passes far enough south in its orbit.

Looking for more? You can always participate in the exciting pastime of slender moonspotting within 24 hours post or prior to the New Moon worldwide. This feat of extreme visual athletics favors the morning of Saturday, September 12th to sight the slim waning crescent Moon the morning before the eclipse, or the evenings of September 13th and 14th, to spy the waxing crescent Moon on the evenings after.

Image credit:
Predicted locations worldwide for the first sightings of the thin waxing/waning crescent Moon.  Image credit: Dave Dickinson

And this eclipse sets us up for the grand finale: the last total lunar eclipse of the ongoing tetrad on September 28th, visible from North America and Europe. And yes, the Moon will be near perigee to boot… expect Super/Blood Moon wackiness to ensue.

Watch for our complete guide to the upcoming lunar eclipse, with observational tips, factoids, eclipse lunacy and more!