aflame, it is not composed of rarefied air like the stars, but rather of earth like the moon; its burning comes not from its composition but rather from its rapid motion. Similarly, he considered the moon and sun to be flat and floating on streams of air. In his theory, when the sun sets it does not pass under the earth, but is merely obscured by higher parts of the earth as it circles around and becomes more distant. Anaximenes likens the motion of the sun and the other celestial bodies around the earth to the way that a cap may be turned around the head. Anaximenes believed that the sky was a dome, and day and night are caused by celestial bodies being carried North until they are no longer seen. There is evidence that suggests Anaximenes may have been the first person to distinguish between planets and fixed stars. Other phenomena Anaximenes used his observations and reasoning to provide causes for other natural phenomena on the earth as well. Earthquakes, he asserted, were the result either of lack of moisture, which causes the earth to break apart because of how parched it is, or of superabundance of water, which also causes cracks in the earth. In either case the earth becomes weakened by its cracks, so that hills collapse and cause earthquakes. Lightning is similarly caused by the violent separation of clouds by the wind, creating a bright, fire-like flash. Rainbows, on the other hand, are formed when densely compressed air is touched by the rays of the sun. These examples show how Anaximenes, like the other Milesian philosophers, looked for the broader picture in nature. They sought unifying causes for diversely occurring events, rather than treating each one on a case-by-case basis, or attributing them to gods or to a personified nature. Influence on philosophy Since language and communication were very limited in his time, Anaximenes's analogies were key in explaining the uncertain through the certain. For example, he knew for certain that blowing air on his hand with his mouth wide open produced hot air, while blowing on his hand with half-closed lips produced cold air. These observations were key in his postulate that the hot air was due to rarefaction and expansion, whereas the cold air was due to condensation and compression. Although in modern times it is known that this is actually the opposite,