Day #8: Thursday, February 6, 1997: We discussed three issues: Precession, eclipses,
and lunar standstills.
Precession of the equinoxes results in a new zodiacal
constellation at vernal equinox approximately very 2000 years.
At the time of vernal equinox between 6000-4000 B. C. the sun
was in Gemini; that period of time is known as the Age of Gemini;
between 4000-2000 B. C. was the Age of Taurus. The sun was in
Taurus at vernal equinox and in Leo at summer solstice; 2000 B.
C. -0 was the Age of Aires; 0- A. D. 2000 is the Age of Pisces;
and some time in the future there will be the age of Aquarius.
Every two thousand years the "event" moves to an earlier
constellation. All our sun signs of western astrology correspond
to the location of the sun during the Age of Aires, not today.
Eclipses: Solar eclipses occur at the time of new
moon; lunar eclipses are associated with the full moon, when the
moon slips into the earth's shadow. The so-called "synodic"
period of the moon, from full moon to full moon as seen from the
earth is 29.5 days; thus there are 14.25 days between a full moon
and a new moon. or between a solar and lunar eclipse
Eclipses only occur during an eclipse season, which
consists of a 30 day period centered on the node of the moon's
orbit. The node occurs when the moon's path crosses the ecliptic.
There are two such eclipse seasons each year. In the fall of 1996,
the node occurred on October 1. There was a full moon on September
26 which was within that eclipse season, and hence there was a
lunar eclipse at that time.
The nodes move through the year due to a slow wobble
of the orbit of the moon which takes 18.6 years. The effect of
that wobble is that eclipses seasons occur 365.24/18.6= 19.6 day
earlier every year. Thus in 1997, the eclipse season of the fall
will be centered about the node 19.6 days earlier than that of
the previous year. There will be another eclipse season in the
spring. During 1997 there will be a total of four eclipses; a
lunar and solar eclipse in March and a similar pair in September.
Only the lunar eclipse of March will be visible in Boulder.
During every eclipse season there can be two eclipses,
one solar and one lunar. If one eclipse is exactly centered at
the node there is the possibility of fitting three eclipses into
Lunar Standstills: Because of the 5.1 degree tilt
of the moon's orbit with respect to the ecliptic, the moon may
be anywhere within 5.1 degrees above or below the ecliptic. During
major standstills the moon reaches a declination of 23.5 plus
5.1 degrees or 28.6 degrees; major standstills occur every 18.6
years. At minor standstill the greatest declination that the moon
reaches is 23.5 minus 5.1 degrees or 18.4 degrees. We are now
in 1996-1997 in the period of minor standstill.
SLIDES: After looking at Fajada Butte, we showed
pictures of Piedra del Sol which marks sunrise on summer solstice
and may contain a petroglyph of the total solar eclipse of July
1097. The pictograph in Chaco below Penasco Blanco may depict
the crab nebula supernova of July 4, A. D. 1054 and the appearance
of Halley's comet of 1066 ( at the time of the Battle of Hastings).
Slides of Chimney Rock showed
a) the appearance of the moon between the double
pinnacles at the last major standstill of 1988; during the end
of the 11th century construction of the Chimney Rock
Pueblo occurred at the time of major standstill.
b) the equinox sunrises appearing between the pinnacles
as seen from the ridge above the Piedra river, west of the Chimneys;
c) the summer solstice sunrise as viewed from the
bedrock basin in which the sun rises just along the northern wall
of the Chacoan great house on the high mesa. The Crab Nebula supernova
of 1054 rose along the southern wall of the great house. That
house thus appears to be an amazing marker of astronomical events
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