36
if it occurs exactly at sunset. Thus, we have three definitions of the equinox which
are not precisely the same: true astronomical equinox when the sun has a declination of 0°, the day at which day and night are (most nearly) of the same length, and
the day at which the sun (most nearly) rises due east or sets due west at a flat horizon. Observationally, therefore, the equinox can be determined either by direct
observation of its declination using a calibrated instrument such as an equatorial
ring (which requires both the concept of a celestial sphere and precise knowledge of
geographical latitude), by measuring the length of day or night, or by observing the
sun’s rising or setting azimuth. All of these methods will have different types of
uncertainties built into them: How precisely can an instrument be aligned and how
accurately is a site’s geographical latitude known? What tool is used to measure the
length of day and night and what is its error? And how flat is the horizon and how
well is the east-west line known?
The aim of this paper is to examine how one particular group—the people of
ancient Mesopotamia, i.e., the area of ancient Iraq and its neighbours, during the
last two millennia BC—conceived of solstices and equinoxes. Even within this
group we may expect some diversity of understanding of these phenomena: the
popular and scholarly conception may have different and even among the literate
elite we should not necessarily expect that the authors of literary works, for example, and the scribes who wrote astronomical texts agreed on precisely what is an
equinox, nor that this understanding remained constant over more than 2000 years.
I begin this paper by presenting a brief overview of Mesopotamian calendars
before examining a range of textual sources which refer to solstices and/or equinoxes in order to try to answer a very basic question: in those texts, were the solstices and/or equinoxes defined calendrically, i.e., by their position in the year,
temporally, i.e., by the length of daylight, or spatially, either with reference to the
place on the horizon when the sun rises or sets or to the intersection of the ecliptic
and the celestial equator, or by a combination of these possibilities?
2 Mesopotamian Calendars
The basic Mesopotamian calendar used over the whole of the period from which we
have written evidence (late fourth millennium BC to first century AD) employed
lunar months which began on the evening of the first visibility (observed or in later
times often calculated) of the new moon crescent (Steele, 2011). A normal year
contained 12 months. In order to keep the calendar in line with the seasons, in certain years an extra “intercalary” month was inserted, usually after either the 6th or
the 12th month of the year. For most of Mesopotamian history, the decision over
when to intercalate was ultimately the decision of the king, and kings could—and
sometimes did—make this decision for short term gain, for example in bringing
forward or delaying the payment of taxes and tributes. Several schemes providing
astronomical criteria for when to intercalate are attested from the early first millennium (Hunger & Reiner, 1975; Ratzon, 2016; Hunger & Steele, 2019: 209–213),
J. Steele
if it occurs exactly at sunset. Thus, we have three definitions of the equinox which
are not precisely the same: true astronomical equinox when the sun has a declination of 0°, the day at which day and night are (most nearly) of the same length, and
the day at which the sun (most nearly) rises due east or sets due west at a flat horizon. Observationally, therefore, the equinox can be determined either by direct
observation of its declination using a calibrated instrument such as an equatorial
ring (which requires both the concept of a celestial sphere and precise knowledge of
geographical latitude), by measuring the length of day or night, or by observing the
sun’s rising or setting azimuth. All of these methods will have different types of
uncertainties built into them: How precisely can an instrument be aligned and how
accurately is a site’s geographical latitude known? What tool is used to measure the
length of day and night and what is its error? And how flat is the horizon and how
well is the east-west line known?
The aim of this paper is to examine how one particular group—the people of
ancient Mesopotamia, i.e., the area of ancient Iraq and its neighbours, during the
last two millennia BC—conceived of solstices and equinoxes. Even within this
group we may expect some diversity of understanding of these phenomena: the
popular and scholarly conception may have different and even among the literate
elite we should not necessarily expect that the authors of literary works, for example, and the scribes who wrote astronomical texts agreed on precisely what is an
equinox, nor that this understanding remained constant over more than 2000 years.
I begin this paper by presenting a brief overview of Mesopotamian calendars
before examining a range of textual sources which refer to solstices and/or equinoxes in order to try to answer a very basic question: in those texts, were the solstices and/or equinoxes defined calendrically, i.e., by their position in the year,
temporally, i.e., by the length of daylight, or spatially, either with reference to the
place on the horizon when the sun rises or sets or to the intersection of the ecliptic
and the celestial equator, or by a combination of these possibilities?
2 Mesopotamian Calendars
The basic Mesopotamian calendar used over the whole of the period from which we
have written evidence (late fourth millennium BC to first century AD) employed
lunar months which began on the evening of the first visibility (observed or in later
times often calculated) of the new moon crescent (Steele, 2011). A normal year
contained 12 months. In order to keep the calendar in line with the seasons, in certain years an extra “intercalary” month was inserted, usually after either the 6th or
the 12th month of the year. For most of Mesopotamian history, the decision over
when to intercalate was ultimately the decision of the king, and kings could—and
sometimes did—make this decision for short term gain, for example in bringing
forward or delaying the payment of taxes and tributes. Several schemes providing
astronomical criteria for when to intercalate are attested from the early first millennium (Hunger & Reiner, 1975; Ratzon, 2016; Hunger & Steele, 2019: 209–213),
J. Steele