In 1978 John McPhee, the wide-ranging nonfiction writer, and Kenneth Deffeyes, a distinguished geologist, saw a UFO. In 1980 McPhee briefly mentioned the sighting in a New Yorker magazine article about their trip across the western U.S. to study the region's geology.  In 1981 the article became a critically praised book, Basin and Range. In 1999 the book went on to win a Pulitzer Prize as part of a four-volume series, Annals of the Former World.
In 2010, as I was enjoying this narrative of geological ramblings, I was surprised at the retelling of the 1978 incident. It occurred early in the evening of November 27 as McPhee and Deffeyes were returning from a rock-collecting expedition near Winnemucca, Nevada:
...a white sphere materialized on our right in the moonless sky. It expanded some, like a cloud. Its light became so bright that we stopped finally and got out and looked up in awe. A smaller object, also spherical, moved out from within the large one, possibly from behind it. There was a Saturn-like ring around the smaller sphere. It moved here and there beside the large one for a few minutes and then went back inside. The story would be all over the papers the following day. The Nevada State Journal would describe a "Mysterious Ball of Light" that had been reported by various people a least a hundred miles in every direction from the place where we had been. 
McPhee then quotes some corroborating testimony from the newspaper story and returns to the geological matters that are the subject of his book. What's jarring about this is that there is no hint of whether he and Deffeyes had speculated about the nature of the phenomenon they had witnessed. After all, this was arguably the most brainpower to witness a UFO since Ezekiel, and the book does testify to the allure of scientific inquiry, albeit with respect to things underfoot rather than overhead.
In the years since the sighting, had they ever learned anything further about it? McPhee can be reached only through his publisher, but Deffeyes has a Web site, so I sent him e-mail. No, he replied, he hadn't heard anything subsequently. He had decided ultimately that they had seen the incandescent trail from a piece of space debris burning up as it reentered the atmosphere. He assumed that the reason the cloud seemed to be essentially motionless was that the object was approaching nearly head-on. 
In setting out to find a convincing explanation for the incident, I expected that I would have to sift through a pile of clues from microfilmed newspaper articles  and whatever I could find on the Internet.  Instead, the first California newspaper account I read contained a fact that would clinch the resolution of the mystery, a fact not known to McPhee and Deffeyes because it wasn't in the Nevada State Journal story: Vandenberg Air Force Base had announced that it had conducted a test launch of a Minuteman missile that evening.  Another California story cited the "second-stage firing" of the missile as the cause of the visible cloud. 
All that remained was to reconcile a rocket launch 500 miles away with the circular object seen by McPhee and the other witnesses in northern Nevada. The object they saw was in the southwest, and the track from Vandenberg to the target area in Kwajalein is southwesterly. The plume of a rocket launched in early evening darkness might become visible in sunlight at a certain altitude and might appear circular to an observer at some distance behind it. 
From various resources on the Web I learned that the Minuteman's second-stage cutoff and third-stage firing occur at an altitude above 50 miles,  which would have been soon after it emerged into sunlight at about 7 PM that evening.  Furthermore, the vapor trail at that height expands outward to form a cone many miles across due to the low atmospheric pressure. Seen from hundreds of miles to the rear, it would have appeared as a circular cloud with an apparent diameter as large as the moon's.  This, evidently, was the large "sphere" seen by McPhee. The "smaller object" that seemed to move within it must have been the third stage rocketing almost directly away.  McPhee and Deffeys therefore must have been almost exactly on the line of flight. I was able to locate a witness from Reno quoted in the Nevada State Journal article who recalled that it was moving to the right as he watched it.  Reno is some 150 miles southwest of McPhee's position, and rightward motion would be consistent with a vantage point to the west of the flight track.
Witnesses to UFOs, and the generally numerically challenged journalists who interview them, don't appreciate the importance of recording certain quantitative information about position and size. Specifically, it is essential to know the compass direction, the angular height above the horizon, and the apparent size. And most observers definitely don't understand that these quantities can only be expressed meaningfully in degrees or other relative terms (e.g. "as wide as my hand when my arm is stretched out").
And so it was with this object. In Ukiah, California, it was reported as being "30 feet from the ground" or "almost touching" the roof of a nearby building.  From Las Vegas, it was seen as "almost three houses wide."  As Deffeyes noted in his e-mail to me, people think these things are a lot closer than they are. Perhaps this is because of their novelty. At any rate, because of the assumption of nearness, observers of this object perceived the object as following them when they moved perpendicular to their line of sight to the object. Because the cloud expanded, some also thought it was moving toward them.
In the face of such ignorance, scientists who would evaluate UFO sightings rationally will always be fighting a losing battle. Deffeyes hinted at this in his response to my question of why McPhee didn't write anything about what they thought they had seen: "I was afraid that we would both become honorary members of the Roswell Society."
Charles Packer email@example.com