Introduction Since ancient times, people have been interested in life on other planets and try to answer the question: “Are we alone in the Universe?” Cosmology and UFOlogy try to find some markers of life on other planets and prove that other forms of life exist in the Universe. The accounts of UFOs have varied, but there seems to be a common syndrome: strange objects in the sky, cylindrical or saucer-shaped, glowing or flickering lights, making beeping noises, darting about at incredible speeds, taking off at odd angles, suddenly standing still, or disappearing. There have been many reports of person encounters with humanoid creatures who came out of these saucers, and even incredible accounts of having been abducted, examined, taken to other galaxies, and then returned to earth. History Until 1572, astronomers viewed the ‘fixed’ stars — fixed and unchanging, that is, in position but also in brightness — as little more than a backdrop to the motions of the planets. In fact, of course, stars do have individual, or ‘proper’, motions across the sky, but the scale of interstellar distances is so immense that light from even the nearest stars takes years to reach us. As a result, proper motions are almost imperceptible, except over very long timescales; and so the Renaissance observer saw the stars in positions seemingly no different from those assigned them by Ptolemy. Another such nova shone forth in 1604, and this one generated alarm and despondency across Europe (Carroll, p. 11). For the first time in eight centuries, the slow-moving planets Jupiter and Saturn were in conjunction in the fateful ‘fiery trigon’ of the zodiac; and no sooner had they been joined there by Mars, than this new star blazed forth in their midst — the most ominous astrological event imaginable. No one could now doubt that changes occurred in the heavens. Indeed, there was talk of another nova that had appeared in the constellation of the Whale, but this was fainter, and had been seen by only a single observer before it faded and vanished. In 1638 the Whale was host to a second nova (or so it seemed); like its predecessor, it faded and vanished — but before its discoverer could publish his account of it, it astonished him by reappearing. It continued to vanish and reappear at intervals, and in 1667 Ismael Boulliau (1605–94) announced that this ‘wonderful star’ was reaching maximum brightness every 11 months: its behavior was to some extent predictable, and therefore law like (Carroll, p. 13). In these lists Herschel carefully compared stars with neighboring ones of similar brightness, so that a variation in one of the stars would reveal itself by disturbing the published comparisons (Carroll, p. 15). The solar system consists of the Sun, a smallish star resident in the suburbs of an average galaxy, and all the lesser objects that are gravitationally bound to it. The solar system has 8 planets and 166 moons. The Sun dominates its system completely; the second-largest object, Jupiter, has only 0.096% the mass and 2% the diameter of the Sun (Carroll, p. 18). There are nine planets and innumerable smaller bodies. Scientists can construct a scale model of the restricted solar system, consisting only of the Sun and the nine planets, to make it easier to grasp the scale of the system. Discussion Suppose that the Sun were the size of an orange. The Earth would then be about the diameter of a sma