The parish records of Westley Church near Bury St Edmunds, west of Cambridge, contain an interesting aside: "The Tenth of May being Tuesday in Anno Domini 1614, there appeared in the air about six of the clock in the afternoon, three suns which were seen by men of good credit for the space of one whole hour."
One might dismiss the observations of these credit-worthy gentlemen as mere hallucination, had not Shakespeare described a similar phenomenon. "Dazzle mine eyes, or do I see three suns?" asks Edward of his brother in Henry VI, and Richard confirms the apparition: "Three glorious suns, each one a perfect sun;
Not separated with the racking clouds, But severed in a plain, clear, shining sky."
Shakespeare plays on words to present the occurrence as auguring advancement for Edward, Richard and their brother George, the three sons of the Duke of York. "Tis wondrous strange," continues Edward:
"I think it 'cites us, brother, to the field,
That we, the sons of brave Plantagenet,
Each one already blazing by our deeds,
Should notwithstanding, join our lights together,
And over-shine the earth, as this the world."
Nowadays, however, we recognise "three suns" as a relatively rare optical phenomenon, variously called "mock suns", "sun dogs", or by meteorologists, "parhelia". The two apparent images of the solar disc are located 22 degrees on either side of the real sun. Each is a very short segment of a solar halo.
A halo occurs when the sun is shielded by a thin cloud of ice crystals. Each crystal resembles a hexagonal cylinder in shape, like a short pencil but tiny by comparison. A ray of light striking one of the sides of a hexagonal prism is refracted, or "bent", as it passes through the ice by an amount close to 22 degrees, so given a more or less random orientation of the crystals, an observer will see the sun surrounded by a complete 22-degree halo.
But ice crystals of this kind do not always orientate themselves in random fashion. If they are predominantly flat - more like a six-sided 50p piece than a pencil - they will tend to settle horizontally, as falling leaves do. If the sun is low in the sky in such circumstances, these "plate crystals" refract light to the observer only from the two sides of where the halo would have been. The more uniform their orientation, the smaller and brighter are the resulting spots on either side of the sun - so much so that they may resemble images of the sun itself.