The constellation of the Dragon consists of the stars that form in Western astronomy Virgo, Libra and Scorpio. Virgo is the head, Scorpio the tail. For the Chinese farmers, the position of the Dragon at sunset indicated the season. No Dragon visible: no growth - its first appearance was the time for preparations and sowing - and when it was completely present in the sky, it was the height of the growing season.
Line 1 The precession is about a half sign of the zodiac in 1000 years. Nowadays the midwinter point is between Scorpio and Sagittarius, so in the year -1000 it was in the middle of Capricorn. When the sun had gone down in the West below the horizon and it became dark, the dragon was approximately at this position.
Line 2 The first appearance of the dragon was about half to end February, when the sun was facing its head, in Pisces. The farmers could start the first activities in the fields. When the dragon emerges, the clouds come in after the dry winter. Later, long after the Shang period, there is the motif of the Dragon with a pearl in its mouth: the full moon of spring sits in the mouth of the Dragon constellation.
Line 3 In the third line, no dragon is mentioned. But it is the time of the year when a lot of work has to be done. The sun is creative all day, from dawn to dusk. The farmer too. The nights are dangerous: the winter cold has not yet left completely, there is danger of night frost. The plants are still small and animals can damage a whole field. Later in summer the plants are too big to be eaten as just one mouthful, and the harm will be less severe.
Line 4 In the year -1000 the vernal equinox was halfway Aries. The dragon reaches from Virgo to Scorpio, Libra is the 'belly'. Around the equinox the sun was facing the dragon's belly. At sunset, the dragon stands with his hind legs behind the horizon, in the abysmal waters. The weather is changing easily, spring has arrived, the sun is already warm but a sudden storm or hail can happen too.
Line 5 From April till August the dragon is entirely visible in the evening. In April in the East and during the whole night, and in July in the West. It is the growing season, the sun stands high and is strong. Everything in nature is provided with lots of energy.
Line 6 When the sun goes to the sign of Virgo, the dragon is going down behind the Western horizon. Nowadays that starts about half September (the stars of Virgo now reach from Virgo 20 to Scorpio 6), but 3000 years ago that was in the beginning of August. It is the end of the growing season. The sun loses its strength, even though it is still summer.
Information from Shaughnessy
and from S. Marshall, "The Mandate of Heaven".
About Dragons in China