mysteries of egyptian zodiacs - HiddenMysteries Information Central

136 6 Method of Astronomical Determination of the Dates Encoded in Egyptian Zodiacs
with the year 4713 B.C,, J. Scaliger decided to number all
the days. For example the Julian day of April 1, 1400 A.D.,
corresponds to the number 2232407 4 .
Figure 6.2: The celestial sphere with the indicated ecliptic,
equator, and the equinox and solstice points. The spring and
autumn equinox points are the intersection points of the ecliptic
with the equator.
On Figure 6.2, besides the ecliptic there is another large
circle marked on the celestial sphere, which is the equator.
This equator is exactly the intersection circle of the plane
containing the Earth’s equator with the celestial sphere. It
is a well-known fact, that the equator circle is relatively fast
changing its position in time. It constantly revolves around
the celestial sphere.
The ecliptic and equator intersect on the celestial sphere
at the angle of 23 o 27 ′ approximately. The points of their intersection
are denoted on Figure 6.2 by the letters Q and R.
In the course of a year, the Sun in its apparent movement
along the ecliptic crosses twice the equator at these points.
The point Q, through which the Sun enters into the northern
hemisphere, is called the spring equinox point. At that
time the day and night are of equal length. The opposite to
Q point on the celestial sphere is the autumn equinox point.
On Figure 6.2, this point is denoted by the letter R. Through
the point R the Sun enters the southern hemisphere. At that
time the day and night are again of equal length.
4 See [27], p. 316.
The winter and summer solstice points are also located on
the ecliptic. The four equinox and solstice points divide the
ecliptic into four equal parts (see Figure 6.2).
As time goes by, the four equinox and solstice points continually
move along the ecliptic in the direction of decreasing
ecliptic longitude. This motion is called in astronomy the
precession of the equinoxes or simply the precession 5 . The
equinoxes drift westward along the ecliptic at the rate of 1 o
per 72 years. This drift caused in the Julian Calendar a shifting
of the dates for the equinox days.
Indeed, since the Julian year is almost the same as the
astronomical year, i.e. the time taken for the Earth to complete
its orbit around the Sun, — the shifting of the spring
equinox on the ecliptic results in shifting of the date of the
spring equinox in Julian calendar (i.e. the “old style date”).
In fact the “old style date” of the spring equinox, which in
the Northern Hemisphere occurs now about March 21, is decreasing
constantly at the rate of one day per 128 years (see
Figure 4.7).
In order to determine positions of celestial objects, we
need a system of coordinates on the celestial sphere. There
are several systems of coordinates used in astronomy, but we
choose the so called system of ecliptic coordinates, which is
illustrated on Figure 6.2. Consider a meridian on the celestial
sphere from the pole P passing through the point A, for
which we would like to determine its coordinates. The meridian
intersects the ecliptic at the point D (see Figure 6.2). The
length of the arc QD will be considered to be the ecliptic longitude
of the point A, and the length of the arc AD — its
ecliptic latitude (the both lengths measured in degrees). Let
us recall that the point Q is the spring equinox point.
In this way, the ecliptic longitude on the celestial sphere
is calculated as a distance from the spring equinox point of
a specific epoch, which was chosen for this purpose. In other
words, the system of ecliptic coordinates is “attached” to certain
fixed epoch. However, once such an epoch is chosen, the
related system of ecliptic coordinates can be used to describe
the positions of the Sun, Moon, the planets, and, in fact, of
any celestial object at any moment of time from this or
another epoch.
In our calculations we used the ecliptic coordinate system
attached to the ecliptic J2000, i.e. on January 1, 2000.
We took, as the basis for the establishment of the ecliptic
coordinates between the zodiacal constellations according to
the ecliptic J2000, their J1900 coordinates (January 1, 1900) 6 .
This partition of the ecliptic fits the contours of the constellations
on an astronomical chart published in [49]. After readjusting
this partition for the J2000 epoch (January 1, 2000),
we obtained the results that are summarized in Table 6.1.
We should explain that the boundaries of the constellations
are not defined precisely on the sky. Therefore, any
5 See [95].
6 See [173], p. 782