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7 Solstices, Equinoxes and the Zodiac
The zodiac—the division of the band through which the sun, moon, and planets
move, into twelve equal length parts (“signs”) each containing 30° (denoted in
Babylonian texts using the linear-measure unit UŠ)—was developed in Babylonia
sometime during the second half of the fifth century BC (Britton, 2010; Steele,
2007, 2018). Although no texts explicitly link the solstices and equinoxes to positions in the zodiac, an implicit connection is made in schemes which link the length
of day to the position of the sun in the ecliptic. Three such schemes are currently
known. All three are what can be termed “rising time schemes”, which operate by
assigning a certain time interval to the time it takes for a given stretch of the zodiac
to rise (Neugebauer, 1953; Rochberg, 2004; Schaumberger, 1955; Steele, 2017).
The first scheme links the rising of stretches of the zodiac to the time intervals
between the culmination of certain stars known as ziqpu stars. It is based upon an
earlier calendar based scheme which associates the setting of the sun on dates in the
schematic calendar with the culmination of the same stars. This calendar based version of the scheme is itself constructed from the simple function for the length of
day and night given in MUL.APIN and therefore places the equinoxes and solstices,
defined by the length of day, on the 15th of Months I, IV, VII, and X in the schematic
360-day calendar. This calendar-based scheme is then transferred across to the
zodiac simply by equating the date in the schematic calendar with the equivalent
position in the zodiac which is then taken to be the position of the sun (e.g. the
equivalent of the 1st day in Month I is 1° in Aries). As a consequence, the sun is
taken to be at 15° in Aries, Cancer, Libra, and Capricorn on the days of the equinoxes and solstices.
The second and third schemes are embedded within the so-called Lunar System
A and Lunar System B systems of mathematical astronomy. In both systems, the
length of day is computed from the sun’s position using a table which is based upon
different rising time schemes. In System A, the days on which day and night are
equal and the days when day is longest and shortest, take place when the sun is at
10° of Aries, Cancer, Libra, and Capricorn. In System B, they take place when the
sun is at 8° of Aries, Cancer, Libra, and Capricorn. A further, poorly attested lunar
system, Lunar System K, places them at 12° of Aries, Cancer, Libra, and Capricorn
(Ossendrijver, 2012: 115).
We therefore have four traditions for the placement of the position at which the
sun is at the solstices and equinoxes: at 15°, 12°, 10°, and 8° of Aries, Cancer, Libra,
and Capricorn. Despite their being incompatible, these four traditions co-existed. I
take this as evidence that positions in the zodiac never became the primary definition of the solstices and equinoxes.
Their Equinox: Mesopotamian Conceptions of Solstices and Equinoxes
7 Solstices, Equinoxes and the Zodiac
The zodiac—the division of the band through which the sun, moon, and planets
move, into twelve equal length parts (“signs”) each containing 30° (denoted in
Babylonian texts using the linear-measure unit UŠ)—was developed in Babylonia
sometime during the second half of the fifth century BC (Britton, 2010; Steele,
2007, 2018). Although no texts explicitly link the solstices and equinoxes to positions in the zodiac, an implicit connection is made in schemes which link the length
of day to the position of the sun in the ecliptic. Three such schemes are currently
known. All three are what can be termed “rising time schemes”, which operate by
assigning a certain time interval to the time it takes for a given stretch of the zodiac
to rise (Neugebauer, 1953; Rochberg, 2004; Schaumberger, 1955; Steele, 2017).
The first scheme links the rising of stretches of the zodiac to the time intervals
between the culmination of certain stars known as ziqpu stars. It is based upon an
earlier calendar based scheme which associates the setting of the sun on dates in the
schematic calendar with the culmination of the same stars. This calendar based version of the scheme is itself constructed from the simple function for the length of
day and night given in MUL.APIN and therefore places the equinoxes and solstices,
defined by the length of day, on the 15th of Months I, IV, VII, and X in the schematic
360-day calendar. This calendar-based scheme is then transferred across to the
zodiac simply by equating the date in the schematic calendar with the equivalent
position in the zodiac which is then taken to be the position of the sun (e.g. the
equivalent of the 1st day in Month I is 1° in Aries). As a consequence, the sun is
taken to be at 15° in Aries, Cancer, Libra, and Capricorn on the days of the equinoxes and solstices.
The second and third schemes are embedded within the so-called Lunar System
A and Lunar System B systems of mathematical astronomy. In both systems, the
length of day is computed from the sun’s position using a table which is based upon
different rising time schemes. In System A, the days on which day and night are
equal and the days when day is longest and shortest, take place when the sun is at
10° of Aries, Cancer, Libra, and Capricorn. In System B, they take place when the
sun is at 8° of Aries, Cancer, Libra, and Capricorn. A further, poorly attested lunar
system, Lunar System K, places them at 12° of Aries, Cancer, Libra, and Capricorn
(Ossendrijver, 2012: 115).
We therefore have four traditions for the placement of the position at which the
sun is at the solstices and equinoxes: at 15°, 12°, 10°, and 8° of Aries, Cancer, Libra,
and Capricorn. Despite their being incompatible, these four traditions co-existed. I
take this as evidence that positions in the zodiac never became the primary definition of the solstices and equinoxes.
Their Equinox: Mesopotamian Conceptions of Solstices and Equinoxes