The Mortimer’s Cross Parhelion: How a Meteorological Phenomenon Changed English History

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A parhelion, or sundog (photo by guigo.eu)

A parhelion, or sundog: Photo by guigo.eu

‘Dazzle mine eyes,’ cries the would-be King Edward in Shakespeare’s Henry VI Part 3, ‘or do I see three suns’? Edward and his army were about to go into the battle of Mortimer’s Cross in 1461 when this scene took place and the sight of ‘three glorious suns, each a perfect sun’ was viewed as a portent, striking terror into the hearts of some and bringing joy to others.

Signs in the sky may be the stuff of legend but in many cases they have their roots in fact. In this case, what the terrified armies saw hanging low on the horizon on a February morning was a meteorological phenomenon called a parhelion (also known as mock suns or sun dogs) in which the sun does indeed appear as if in triplicate, three heavenly bodies side by side.

What Causes a Parhelion?

Parhelia are easily explained by the process of refraction, in which light is bent or split as it passes through solid but clear objects such as raindrops. The most common and obvious example of the refraction of sunlight is the splitting of light into its constituent colours as it passes through rain showers to form a rainbow.

In the case of the parhelion, and another closely related meteorological phenomenon, the halo, (which appears as a ring of light around the sun), the sun’s rays are refracted not through water but through ice. Parhelia form only under particular circumstances: they are associated with high-level clouds and require flat crystals which must be larger than 30 micrometres.

The parhelion phenomenon differs from the halo in that it requires the ice crystals to be broadly horizontally aligned. The refraction ‘bends’ the rays by 22 degrees, causing the appearance of the two ‘false suns’ on either side of the real thing – although, as Chiu Hung-yu notes, the perfect parhelion is not always observed and, if one of the two ‘false suns’ is obscured, just two  suns may be visible.

Where do Parhelia Occur?

Because they depend on a specific set of meteorological conditions to occur, parhelia are by no means as common as rainbows, but they nevertheless do occur regularly, year-round, as long as the necessary conditions are met.  Dr. Hugh Pumphrey, of Edinburgh University, describes these conditions as, “a day with few or no low clouds and a thin veil of higher clouds with the right sort of ice crystals in them.”

Dr Pumphrey also told Decoded Science that, in his experience, parhelia are more likely to be visible when the sun is low. (This is borne out by the Oxford Reference Dictionary of Astronomy’s assertion that they ‘disappear when the Sun’s altitude exceeds 60 degrees’).  Indeed, Dr Pumphrey notes that the phenomenon is “commoner than most people think… because people don’t tend to look towards the Sun much.”

The Implications of the Mortimer’s Cross Parhelion

The sunburst became the badge of King Edward IV (photo by Richard Croft)

The sunburst became the badge of King Edward IV (photo by Richard Croft)

The triple sun which occurred at Mortimer’s Cross was auspicious for Edward of York. The three suns were taken to represent him and his two brothers – the three sons of the Duke of York, claimant to the English throne, who had been killed just weeks previously. The novelist and historian Philippa Gregory notes that that Edward ‘was quick-witted enough to assure his army that it foretold their victory.’

It is tempting to speculate that the superstitions of the participants over-rode their common sense and that they believed the result to be predetermined – meaning that the appearance of the parhelion did, in fact, deliver the battle to the Yorkists. King Edward IV, as Edward of York later became, certainly seems to have thought so – he was to incorporate the sun into his personal badge.

Sources

Hung-yu, C. In-depth anatomy of the atmospheric optical phenomenon – ‘sun dog’. Hong Kong Observatory. Accessed 29 September 2011.

Gregory, P., Baldwin, D., Jones, M. The Women of the Cousins’ War. Simon & Schuster. (2011).

NOAA National Weather Service. Parhelion. Accessed 29 September 2011.

Ridpath, I A Dictionary of AstronomyOxford University Press, 2007. Oxford Reference Online. Accessed 2 October 2011.

University of Illinois. Sundogs. Accessed 29 September 2011.

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© Copyright 2011 Jennifer Young, All rights Reserved. Written For: Decoded Science
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