At approximately 8:10 pm, i was completing a scenic walk when i noticed an unusually intense light moving west to east (left to right). my initial thought was that it was an aircraft that had illuminated its landing lights; i waited for the landing light to decrease in intensity as it passed me and for the navigation lights and strobes to become visible. instead, the object continued to proceed east and its luminosity never changed, no nav lights became visible, and the object produced no prop or turbine noise. it was, in fact, utterly silent. i was able to track the object for approximately 5 minutes - it never wavered from its flight path but when it approached what appeared to be conflicting traffic on extended approach to logan, it dimmed quickly and was suddenly no longer visible. it did not "wink" off, but it appeared to become incrementally dimmer so that the transition from full brightness to invisibility took perhaps 1.5 seconds. i am a pilot, aviation attorney, former managing director at united airlines for regulatory, and have spent my life in and around aircraft. i can identify commercial and military and historic aircraft with ease - the characteristics which distinguished this object from a fixed wing aircraft, helicopter, or lighter than air aircraft were (1) the exceptional brightness of the object (or it's lighting), (2) the slow airspeed, (3) obvious lack of any navigational or strobe lights, (3) absence of any prop noise or turbine noise (the latter when the object had passed from my left to right; even the quietest high-bypass turbine produces noise at idle thrust), (4) sudden dimming of object to invisibility when it appeared to be in the same vicinity of a conventional aircraft. obviously, this is not the most dramatic report of its type, but i am hoping you receive more reports that substantiate the existence of this unusual vehicle.