Bizarre light seen streaking across the clear and cloudless evening sky, covering 120 (+ or -) degrees of arc in 15-20 sec..I had just completed my nightly walk on the 9-hole Harrington Golf Course, and was standing beside the practice putting green, located at the north end of the course. I had paused, to enjoy the beautifully clear, almost cloudless, night sky. I was facing generally north-northeast, and could see the star, Capella (I believe), almost straight in front of me, just to the left of the town water tower, and at approximately 20 degrees angle of elevation.My attention was suddenly drawn upward to a fast-moving light, the approximate size and luminosity of the International Space Station (ISS). When I first observed it, I estimate that it was located approximately 30-50 degrees to the left (west) of Capella, and at approximately 60-70 degrees angle of elevation. During the first instant I saw the light, as it coursed toward the east in the northern sky, I assumed that it was probably the ISS, or perhaps the German ROSAT satellite, which is currently anticipated to re-enter the Earth’s atmosphere at sometime between October 22-24, 2011.However, within probably a second, or so, of my first having sighted the light, I realized that it was not the ISS, which I have witnessed on many occasions, and that the object's angular velocity across the sky was far too high for the object to be either the ISS, or any other man-made orbiting object. Whereas a typical satellite in low-Earth orbit has a maximum angular velocity in the vicinity of one degree per second, the object in question appeared to be moving at perhaps 5+ degrees per second. My impression was that it was "streaking" across the sky.In addition, the object may have had a very faint blue, or perhaps purple, tinge to it. Its color was not quite that of a typical star in the night sky, although the color distinction was very faint.The object continued coursing to the east, and disappeared from my sight when I could no longer resolve it visually. It did not fade out, as satellites are seen to do when they enter the Earth’s shadow (or "terminator"). It simply got smaller, until I could no longer resolve it visually.I immediately opened my cell telephone, and noted the time to be 18:42 hrs. (PDT), and it took approximately 30 seconds for the indicated time to turn over to 18:43 hrs.. Consequently, assuming that cell phone time is accurate, the time of the sighting may have been 18:42::30 hrs. (PDT). The object coursed from approximately 340 degrees (true) to approximately 90-95 degrees (true) in, I estimate, 15-20 seconds, again, at a much higher angular velocity than satellites are seen to move across the sky.The event is somewhat complicated by the fact that the ROSAT satellite had passed through the same general area of the sky some eight minutes before my sighting. The website, www.Heavens-Above.com, indicates that ROSAT was first visible in the northwest sky at 20:34::37 on the same date as my sighting, October 17, and that it would have been at an angle of elevation of 56 degrees, at its highest elevation. However, that satellite would have traveled from the northwest sky to the south-southeast sky over the course of 240 seconds, at a much lower angular velocity than that of the object I observed.I considered the possibility that the object might have been a fragment of the ROSAT satellite, but even that possibility does not seem feasible. The object disappeared from my sight when it was within a few degrees of true east, and the ROSAT had coursed to the southeast, approximately 4 minutes earlier.I also considered whether the object could have been a meteor, but that does not make sense, either. Its luminosity did not fluctuate during the entire sighting, and no fragments were seen falling from it. Moreover, 20 seconds is a very long burn-time for a meteor, particularly a small meteor, and there was no terminal burst, which commonly is seen for long-duration meteors.This event has me thoroughly confused!! This was a very strange occurrence, for which I have no ready explanation!!I hold a commercial pilot rating, and I am a former flight instructor. In addition, I am a frequent and avid viewer of the night sky, and am able to identify many of the heavenly bodies and constellations by name. I own a number of reflector telescopes, and several pairs of high-quality astronomical binoculars, all used for night sky viewing.