Archaeoastronomy

Archaeoastronomy is the practical use of astronomy as it applies to early cultures. It is of interest to astronomers and archaeologists because it encompasses the study of astronomical principles employed in ancient works of architecture (sometimes referred to as astroarchaeology) as well as the practice of astronomy and methods of observations among ancient peoples.

ORIGINS OF ASTRONOMY AND ASTRONOMICAL OBSERVATIONS

    The importance of astronomy to all ancient cultures stemmed from a practical need to establish a precise method for telling time, monitoring agricultural events, performing religious ceremonies, and regulating governmental activities. Early people discovered that the systematic progression of the seasons was matched to the rhythmic motions of the heavens, and that the sky was a far more accurate indicator of these cycles than making systematic observations of the weather.
    People realized that the movement of the sun across the sky could fix the day and its divisions, while the changing phases of the moon established the month ("moonth" in Old English). By observing the rising or setting of a specific star when near the sun (heliacal rising or setting), the year could be defined. And, because there were seven objects which moved against the starry background; five planets, the moon, and the sun, the popular notion of the week came to fore.
    Ancient cultures did not understand the true physical nature of these seven wanderers in the heavens, so it was only natural to deify them and to closely monitor their changing positions. Those individuals who became proficient in these tasks were able to wield enormous power with the populace and ruling infrastructures; so much so, that they were venerated as priests and allowed to exist as a separate, almost untouchable segment of society. They designed temples with astronomical alignments to track the extreme positions of the sun and the moon. In a sense, these structures acted as permanent calendars. Eventually, in the Middle East, a complex series of rules were devised to relate this celestial dance as an indicator of human destiny. The pseudoscience of astrology with its many different types of horoscopes was a direct result of this synthesis.

THE ANASAZI INDIANS OF THE SOUTHWESTERN US

    About 500 AD, Indians who lived in the upper Rio Grande, Colorado, and San Juan river basins of what is today, Utah, Colorado, Arizona, and New Mexico, began to abandon their nomadic existence for the richer rewards of a more stable and settled agrarian lifestyle. Instead of seasonal migrations from region to region, as hunters and gatherers, crops were planted on a regular basis to insure a more consistent and varied food supply. In good years, food surpluses were realized which helped sustain villages against times of famine. Collectively these people were known as the Anasazi, a Navajo word meaning "ancient ones" or "ancient enemies." The Navajo never knew the Anasazi, for when they migrated into the Four Corners area during the fifteenth century, they only discovered their silent ruins.
    The Anasazi lived in harmony with nature, and as a result they were keen observers of the earth and the heavens. Most of their waking hours were spent out-of-doors surrounded by blue sky and yellow rock. They could tell impending weather changes by monitoring insect activity or wind direction. The rhythmic changes of the heavens set the tone for daily, monthly, and yearly calendric cycles. Farming was difficult because rainfall was scarce. Most of the annual precipitation came in short bursts, during thunderstorms which occurred mainly in the spring and summer months. Temperatures could range from -10° F on the coldest winter mornings to around 100° F on many summer afternoons.
    The Anasazi dwelled in family or clan units on mesa tops or in the many protective enclaves afforded by surrounding cliff walls. They built their pueblos (towns) and ceremonial structures from the abundant sandstone rock which was all around them. A distinctive feature of pueblo architecture was the kiva, a roofed ceremonial room, found usually below ground level, and almost always reserved for males. This may possibly be explained by the fact that Anasazi society was matriarchal. Women held property rights, and family names were passed down through the wife? relations. Divorce, Anasazi style, was simply the wife putting the husband? belongings outside of her pueblo. Men and boys had to have a place to congregate, and the kiva was thought to be used to that practical end.
    Anasazi men and women were short and lean. Average heights were about five feet, slightly higher for men and lower for women. Weights were about 100 pounds. Life spans averaged under 30 years with men living longer than women. Arthritis and bad teeth were often contributing factors to an early grave, as well as a high child mortality rate.

EARLY CULTURES AND THE SKY

What were the conditions which allowed ancient people to make good astronomical observations thousands of years ago? The culture had to possess a
1. Functioning language or some method of communication
2. Practical, working knowledge of mathematical principles
3. Sufficient longevity of its population to observe the repetition of cyclical events
Early people probably did not understand the relationships in movements between the earth, moon, and sun. They were, however, able to measure their positions and establish alignments which served as monitoring devices.
Objects and observations of interest to early humans
1. Sun: Solstitial sunrise and sunset positions. For the northern hemisphere, the sun rises at its most northerly and southerly positions on the dates of June 21 and December 21 respectively.
2. Moon: Major and minor standstill positions. These represent the extreme positions of moonrise and moonset along the horizon.
3. Helical rising of a star: This was not applicable for Stonehenge, but the Egyptian's first observations of Sirius before sunrise pinpointed their year and the annual flooding of the Nile River.
4. Bright Stars and their rising positions: Certain stars signal seasonal changes.
5. Conjunctions (objects appear close together in the sky) and eclipses of the sun and of the moon.
Methods of observation
1. Introduction
  1. Menhir: Standing stones which were used as positional markers, usually associated with European megalithic sites.
  2. Foresight: A distant mountain or conspicuous geographical feature which the sun rises or sets behind.
  3. Backsight: The position from which the observations are conducted.
2. Stationary observer: The observer watches the changing position of the rising or setting sun against the features of a distant horizon. Stone circles or other isolated menhirs between the backsight and foresight could have been used as markers to indicate the extreme positions of the sun or moon or other religious and agricultural events. In this manner a calendar could have been established. The use of intervening menhirs in American Indian observations did not usually occur.
3. Observer moves: Distinctive notches on hillsides located miles away from the observer could have been used as foresights. The observer would have positioned himself (at a backsight) so that each day the sun would have risen or set behind the same geographical point, i.e., a notch in a mountain peak. Since the location of the sun would have shifted from one day to the next, the observer would have continuously changed his backsight location to keep the sun rising behind the same geographical location. He could have marked these changing positions with a series of stones. He would have easily noticed when the solstice occurred (longest or shortest day of the year, marked by the most northerly or southerly rising positions of the sun), since afterwards, he would have been retracing his steps as the sun moved in the opposite direction.
4. Windows/Ports (small openings) and doorways, etc.: A building is designed in such a manner that hallways/doors/windows (ports) permit the passage of sunlight or moonlight into certain parts of the structure at certain key times of the year or when these objects are in certain key positions. The entire structures themselves or the alignment of ports create the markers which can be used to establish a yearly calendar.
5. Sun Daggers: The passage of sunlight through natural or contrived rock formations creates a dagger-like image on another rock face at certain key times of the year. The most famous of these observatories is the sun dagger atop Fajada Butte in Chaco Culture National Historical Park in northern New Mexico.
Stonehenge: Europe's best known and most visited megalithic observatory
1. Introductory remarks
  1. Megalithic astronomy: Deals with structures built from large stones which have an astronomical relationship. Megalith means large stone.
  2. What was Stonehenge? A megalithic calendar used to monitor the positional movements of the sun and moon for agricultural purposes and possibly for use as a computational device for the prediction of lunar eclipses.
  3. Location: In south central England, about two hours west of London, near the town of Salisbury, just off Route A344.
  4. Size: Smaller than expected, especially when viewed from the perimeter fence, but impressive when walking within the stone circle and horseshoe.
  5. Description: A very shallow round ditch, flanked internally by a low bank (320 feet in diameter) is concentric with a circular group of standing stones, called sarsens (100 feet in diameter), capped with lintels. Inside of the sarsen circle there are five huge freestanding trilithons (three are still complete) shaped like a horseshoe with the open end pointed to the northeast, toward a large menhir called the heel stone, about 70 feet from the ditch and 256 feet from the center of the monument. See the map of Stonehenge on the next page.
  6. Stonehenge nomenclature
    1. Sarsen: Name given to the large uprights (25-50 tons) which form the circle and central horseshoe. It is also the name of the rock itself. These were found at Marlborough Downs, 20 miles to the north of the monument.
    2. Lintel: Term used to denote the cross slabs of worked stone which lie on top of the sarsens.
    3. Bluestones: Smaller stones (five tons apiece) which were transported mostly by water from the Prescelly Mountains of southern Wales to Salisbury Plain. Their significance is unknown.
    4. Trilithons: Name given to the five freestanding sarsen and lintel caps which form the central horseshoe. These were used as key seasonal markers.
    5. Heel stone: A large menhir about 256 feet to the northeast from the center of the Stonehenge structure. The sun rises over the heel stone on the summer solstice.
    6. Aubrey holes: A series of 56 holes spaced at 16 foot intervals forming a circle 288 feet in diameter. They may have been used as a predictor for lunar eclipses.
    7. 'Y' and 'Z' holes: There are 30 Y holes and 29 Z holes. The Y's form a circle about 35 feet outside of the sarsen circle, and the Z's form a smaller circle lying from five to 15 feet outside of the sarsen circle. They may have been used to measure the phase period of the moon, which is 29-1/2 days. Even though there is a number 30 Z hole, Z hole 8 is missing, allowing for only 29 Z's. Sometimes the Aubrey holes are referred to as the X holes.
    8. Station stones: Originally there were four sarsen stones in the shape of a rectangle (two are missing) which paralleled the axis of the summer solstice sunrise.
2. The construction of Stonehenge: Three major phases
  1. Stonehenge I: Ditch-bank circle, four small post holes, two larger post holes, heel stone plus narrow circular ditch, 56 Aubrey holes
    1. Date: 2800 BC
    2. Construction period: 40 years
    3. People: Late Stone Age people (Windmill People) who came from Europe (4300 BC) bringing with them agriculture, cattle, primitive wheat,flint, bone tools and pottery. They built long earthen barrows for the burial of their dead.
  2. Stonehenge II: Bluestones were erected in two concentric circles about six feet apart and 35 feet from the monument's center. This construction was never completed. The old ditch-bank entrance was widened by 25 feet, construction of the Stonehenge avenue to the Avon river two miles away. The station stones were thought to have been placed at this time.
    1. Date: 2130 BC
    2. Construction period: less than 100 years
    3. People: Beaker people. Came from Holland and the Rhineland (Germany). They introduced the use of worked metal and beer to Britain and dominated the economy of southern England. They got their name from the elaborate clay beakers they often buried with their dead.
  3. Stonehenge III:
    1. Date: 2075 BC
    2. Construction period: 50 years
    3. People: Wessex people. The blending of various clans of Beaker people formed the Wessex group. Dominated by a wealthy, powerful aristocracy whose trade routes extended into central Europe, Ireland, Crete and Greece (Bronze Age).
    4. Three different periods of construction
      1. Erection of trilithons in the horseshoe pattern (45-50 ton uprights) and the outer ring of sarsens and lintels (25 ton uprights). Erection of slaughter stone? Double circle of bluestones were removed to an unknown location.
      2. Erection of bluestone oval within the trilithon horseshoe, 'Y' and 'Z' holes dug, bluestone oval dismantled, erection of altar stone at the monument's center.
      3. Erection of bluestones in a horseshoe pattern within the trilithon structure to match its shape, and a bluestone oval between the trilithons and the outer sarsen circle.
Numerous alignments at Stonehenge were discovered by Gerald Hawkins in the mid 1960's. They can be divided into two main groups
1. Group one: Alignments involving Stonehenge I
  1. Sun: Summer and winter solstice sunrise and sunset alignments
  2. Moon: Northern and southern major and minor standstill alignments.
2. Alignments involving the sarsens of Stonehenge III
  1. Sun: Summer and winter solstice sunrise and sunset positions
  2. Moon: Northern and southern major and minor standstill positions