The answer is, yes—at least until they are identified.
A common UFO report is of an object that rapidly changes color, moves anomalously, and, sometimes, follows the observer. Disappointing as it may be to those who hope for close encounters with intelligent aliens, the two culprits usually responsible for such displays are the planet Venus and the brightest star in the night sky, Sirius.
At its most brilliant, Venus creates the iIlusion of being closer than it is, and may appear to trail after the observer. Sirius, being one of the brightest point sources in the sky, twinkles violently, especially when it is near the horizon. Twinkling, or scintillation, can involve rapid color changes and is caused by turbulence in the air.
Other common UFOs are fireballs, planetary conjunctions, glinting or flashing satellites, and reentering space debris. None, however, can be attributed to alien spacecraft.
