Lecture notes:

Day #7: Tuesday, February 4, 1997: The major points of the lecture were:
I. The constellation of Leo and the four ancient constellations which marked the solstices and equinoxes in the period 4000-2000 B.C.
II. The effect of precession upon those constellations: there is a shift of one constellation every 2000 years, such that the sun signs of western astrology are all off by one constellation.
III. The defining features of the Chaco Culture:
  1. Great Houses
  2. Roads
  3. Outlying communities
  4. Astronomy
IV. Pilgrimage into Chaco demanded an accurate calendar and caused the growth of astronomical knowledge.
I. In the period of 4000-2000 B.C. four major constellations along the ecliptic may have been identified with the cosmic cycle of time and the life of the universe:
  1. Vernal equinox: Taurus, the bull as major symbol of fertility.
  2. Summer solstice: Leo, the solar lion, the symbol of supreme power.
  3. Autumnal equinox: Scorpio, the night spider who wounds the sun causing his decline and eventual.
  4. Winter solstice: Aquarius, a symbol of water and death in the waters of chaos.
These four ancient constellations are thus not simply silly and cute figures in the sky but powerful symbols for people who lived at that time. There were also four "Royal Stars" connected with that sequence of time and movement of the sun along the ecliptic:
  1. Vernal equinox- Aldebaran
  2. Summer solstice- Regulus
  3. Autumnal equinox- Antares, the heart of the Scoripion
  4. Winter Solstice- Fomalhaut in Pisces Pisces austrinus (the southern fish).
CONSTELLATION OF THE WEEK: Leo; brightest star Regulus "Little King" a name given it by Copernicus; Arabic:"El Kalb al Asad", the heart of the Lion ; second brightest Denebola, Arabic "El Dhanab al Asad" the tail of the Lion. Regulus is 85 light years away, 160 times brighter than the sun, 5 times larger then the sun, and quite hot: 13,000 K.
II. Because of the 26,000 year precession of the earth's axis of rotation there is a gradual change of the constellation which the sun passes at solstices and equinoxes. Another effect of precession is the presence or absence of a star near the north celestial pole. Polaris is a relative newcomer; prior to a few hundred years ago there was no bright star close to the pole until we reach 2600 B.C. when Thuban was in place for a few centuries.
III. Chaco- Pueblo II period A. D. 900-1100
  1. Center of a vast system of more than 100 outlying communities covering an area more than 100 miles across.
  2. Great Houses: built for the ages; with middens( trash heaps) containing hundreds of thousands of broken pots; largely vacant, with only perhaps 1/4 of the rooms used by permanent occupants.
  3. Roads: 30 feet wide with curbing and berms; straight; great north road within 1 degree of true north between Chaco and the San Juan river; steep stairways into the canyon
  4. Astronomy: Fajada butte; north-south alignments of structures; crab nebula (1054); Halley's comet (1066); total eclipse (1097).

IV. What does it all mean? Why such a sudden growth of a complex society with its sophisticated astronomy? The explanation may be that it functioned as a pilgrimage center, such that on certain days (perhaps full moon of winter solstice) thousands of people walked into the Canyon to participate in festivals. When walking in, the pilgrims would have used the wide roads, as sort of a parade, and steep stairs. They would have spend a few nights in the great houses.

Since is it necessary to arrive at such a festival on time, an accurate calendar (accurate to one day) was absolutely necessary and as a result astronomy was developed. Another place in the world where astronomy was driven by religion and pilgrimage is Islam where devout Muslims must face Mecca for their prayers, mosques must point toward Mecca. The "qibla" is the direction to Mecca, and Arabic astronomy was developed to determine the direction of the qibla all over the Islamic world.
The calendar in the Chaco culture was probably established by the appearance of the sun behind features of the horizon. At Wijiji, the sun appears in a notch on the southeastern horizon at winter solstice. At Chimney Rock, the sun appears between the two pinnacles at equinox. Because of its many calendrical stations, Chimney Rock may have functioned at the "Greenwich Observatory" of the Chaco system, measuring the calendar and signalling dates down to Pueblo Alto.

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