The moon's orbit likewise intersects the apparent path of the sun in two points, its two nodes; and the interval of time between its passage through one of these nodes and its return to that same node again is called a Draconic month, a month of the Dragon. The same symbols are applied by analogy to the moon's nodes. Indeed the "Dragon's Head," ☊, is the general sign for the ascending node of any orbit, whether of moon, planet or comet, and the "Dragon's Tail," ☋, for the descending node. We not only use these signs in astronomical works to-day, but the latter sign frequently occurs, figured exactly as we figure it now, on Babylonian boundary stones 3000 years old. But an eclipse either of the sun or of the moon can only take place when the latter is near one of its two nodes--is in the "Dragon's Head" or in the "Dragon's Tail." This relation might be briefly expressed by saying that the Dragon--that is of the nodes--causes the eclipse. Hence the numerous myths, found in so many nations, which relate how "a dragon devours the sun (or moon)" at the time of an eclipse. [Illustration: HYDRA AND THE NEIGHBOURING CONSTELLATIONS.] The dragon of eclipse finds its way into Hindoo mythology in a form which shows clearly that the myth arose from a misunderstanding of the constellations. The equatorial Water-snake, stretching from one node nearly to the other, has resting upon it, _Crater_, the Cup. Combining this with the expression for the two nodes, the Hindu myth has taken the following form. The gods churned the surface of the sea to make the Amrita Cup, the cup of the water of life. "And while the gods were drinking that nectar after which they had so much hankered, a Danava, named Rahu, was drinking it in the guise of a god. And when the nectar had only reached Rahu's throat, the sun and the moon discovered him, and communicated the fact to the gods." Rahu's head was at once cut off, but, as the nectar had reached thus far, it was immortal, and rose to the sky. "From that time hath arisen a long-standing quarrel between Rahu's head and the sun and moon," and the head swallows them from time to time, causing eclipses. Rahu's head marks the ascending, Ketu, the tail, the descending node.