When pigs fly

I have a few questions about the origin of the phrase "when pigs fly". I recently watched a History Channel program called Ancient Aliens. The episode was about art and writing throughout history that could be interpreted as describing various technologies, UFO sightings, and alien beings. It caught my attention when they spoke of John Winthrop’s book, The History of New England, 1630-1639.
"One night in March of 1638 or 1639, James Everell ("a sober, discreet man"- Winthrop) and two companions boarded a little boat and set out for a trip on the Muddy River in Boston. They had been moving downstream for about a mile when the night's mysterious events began. The three men were suddenly confronted with the appearance of a huge, bright light hovering in the sky. The light "flamed up" as it hovered and appeared to be about "three yards square." As they watched, the light "contracted into the figure of a swine" and moved "swift as an arrow" in the direction of Charlton."

Rense.com, Pittman, Christopher W., ‘A Great Light in the Sky’ –First UFO Sighting in North America, http://www.rense.com/general3/light.htm
In the article, the author says, "The witnesses' account presents some perplexing aspects. What precisely is meant when the object is described as "the figure of a swine?" It is difficult to imagine anyone seriously reporting a sighting of a flying pig."

Obviously they reported it, which is where my question comes in. Would it be fair to say that the phrase "when pigs fly" originated from this event? Could it have been originally used, perhaps phrased a different way, to mock James Everell and then later associated with impossibility?

• Re: When pigs fly Gary Martin 08/September/10 (1)
  • Re: When pigs fly ESC 08/September/10 (0)