46
8 Conclusion
Main aim in this paper has been to gather the evidence for how the solstices and
equinoxes were conceived by scholars in ancient Mesopotamia. This evidence
clearly shows that the primary definition of the solstices and equinoxes was linked
to the length of day and night: the solstices were the days on which the day was
either longest or shortest, and the equinoxes were the days when day and night were
of equal length. The dates of the solstices and equinoxes were considered to be
equally spaced through the year, either at 3 month intervals in the 360-day schematic calendar or on dates in the real luni-solar calendar which correspond to equal
divisions of the solar year (the Babylonians never distinguished between the tropical and sidereal year and so it is appropriate to talk merely of the solar year). A
secondary definition of the solstice and equinoxes was therefore calendrical. In
addition, solstices were also defined as the date on which the sun rose at its most
northerly or southerly point on the horizon, providing a tertiary definition of the
phenomenon. Equinoxes, however, do not seem to have shared this tertiary definition referring to the rising point of the sun.
Given that the primary definition of the solstices and equinoxes related to the
length of day and night, it is appropriate to ask how the Babylonians were able to
identify when these phenomena took place. What evidence we have of Babylonian
time measurement suggests that water clocks were used to measure intervals of time
in astronomical contexts. These water clocks, however, were far from accurate:
studies of Babylonian timings of eclipses show that timings of more than a few
hours often had errors of up to half an hour (Fermor & Steele, 2000; Steele, 2000).
Thus, determining when day and night were of equal length or when the day was
longest or shortest would have presented many challenges for the Babylonian
astronomers and likely produced quite inaccurate results. Similarly, although the
position on the horizon where the sun rises at its most northerly or southerly point
can fairly easily be measured, because the sun’s rising point changes very slowly
around the solstices deciding when the sun had reached this point is very difficult.
It is therefore not apparent how the Babylonians observed these phenomena.
Observations or solstices and equinoxes must have been made at least occasionally, however. As discussed in Sect. 5, we have four reports of solstices or equinoxes
contained in repots sent to the Neo-Assyrian king, and as noted in Sect. 7, although
most reports of solstices and equinoxes found in the Late Babylonian Diaries and
related texts were computed according to a fairly simple scheme, at least some
reports of these phenomena dating to before the fourth century BC seem to refer to
observations rather than computations. Furthermore, the 19-year scheme for the
dates of the solstices and equinoxes which operated after the fourth century must
also have been based upon at least one observation to provide a start date for the
scheme. The scheme places the solstices and equinoxes at equally spaced intervals
in the solar year. However, because the sun’s velocity is not constant, the solstices
and equinoxes are in fact not equally spaced: in the late first millennium BC, the
interval between the spring equinox and the summer solstice was about 2 days
J. Steele
8 Conclusion
Main aim in this paper has been to gather the evidence for how the solstices and
equinoxes were conceived by scholars in ancient Mesopotamia. This evidence
clearly shows that the primary definition of the solstices and equinoxes was linked
to the length of day and night: the solstices were the days on which the day was
either longest or shortest, and the equinoxes were the days when day and night were
of equal length. The dates of the solstices and equinoxes were considered to be
equally spaced through the year, either at 3 month intervals in the 360-day schematic calendar or on dates in the real luni-solar calendar which correspond to equal
divisions of the solar year (the Babylonians never distinguished between the tropical and sidereal year and so it is appropriate to talk merely of the solar year). A
secondary definition of the solstice and equinoxes was therefore calendrical. In
addition, solstices were also defined as the date on which the sun rose at its most
northerly or southerly point on the horizon, providing a tertiary definition of the
phenomenon. Equinoxes, however, do not seem to have shared this tertiary definition referring to the rising point of the sun.
Given that the primary definition of the solstices and equinoxes related to the
length of day and night, it is appropriate to ask how the Babylonians were able to
identify when these phenomena took place. What evidence we have of Babylonian
time measurement suggests that water clocks were used to measure intervals of time
in astronomical contexts. These water clocks, however, were far from accurate:
studies of Babylonian timings of eclipses show that timings of more than a few
hours often had errors of up to half an hour (Fermor & Steele, 2000; Steele, 2000).
Thus, determining when day and night were of equal length or when the day was
longest or shortest would have presented many challenges for the Babylonian
astronomers and likely produced quite inaccurate results. Similarly, although the
position on the horizon where the sun rises at its most northerly or southerly point
can fairly easily be measured, because the sun’s rising point changes very slowly
around the solstices deciding when the sun had reached this point is very difficult.
It is therefore not apparent how the Babylonians observed these phenomena.
Observations or solstices and equinoxes must have been made at least occasionally, however. As discussed in Sect. 5, we have four reports of solstices or equinoxes
contained in repots sent to the Neo-Assyrian king, and as noted in Sect. 7, although
most reports of solstices and equinoxes found in the Late Babylonian Diaries and
related texts were computed according to a fairly simple scheme, at least some
reports of these phenomena dating to before the fourth century BC seem to refer to
observations rather than computations. Furthermore, the 19-year scheme for the
dates of the solstices and equinoxes which operated after the fourth century must
also have been based upon at least one observation to provide a start date for the
scheme. The scheme places the solstices and equinoxes at equally spaced intervals
in the solar year. However, because the sun’s velocity is not constant, the solstices
and equinoxes are in fact not equally spaced: in the late first millennium BC, the
interval between the spring equinox and the summer solstice was about 2 days
J. Steele