1 ARCHAEOASTRONOMY Thursday meeting – January Roberta Zanin

2 Archaeoastronomy: the study of the practice of astronomy using both the written and unwritten records. It began as a meeting ground for three established disciplines: (A.Aveni-Journal of Archaeological Research,Vol.11, No.2, 2003) Astroarchaeology: a methodology for retrieving astronomical information from the study of alignments associated with ancient architecture. (Hawkins, 1966) History of Astronomy: it is concerned with acquisition of precise knowledge by ancient cultures. (Crowe and Down, 1999) Ethnoastronomy: a branch of cultural anthropology that develops an understanding of cultural behavior as gleaned from indigenous perceptions of events in the heaven. (Fabian, 2001) 1

3 Outline Astroarchaeonomy two examples of building alignments: 1.Stonehenge 2. Chichén Iztá (Mexico), the Caracol and El Castillo as proof of the perfect astronomical knowledge of these two ancient cultures. History of astronomy how this knowledge could be obtained without any modern instruments 1. how to predict an eclipse 2. how to measure the cycle of celestial bodies Conclusions Ethnoastronomy 2

4 Stonehenge Phase I ( BC): a circular bank with a ditch, inside the bank a circle of the 56 Aubrey holes. An earthwork, called Avenue, along which the Heel Stone was located. Phase II ( BC): Aubrey holes partially filled, wooden settings in the center and at the eastern entrance. Phase III ( BC): a circle of Sarsens within a horseshoe- shaped arrangement of Trilithons and four great stones as stations. 3

5 Stonehenge Phase I ( BC): a circular bank with a ditch, inside the bank a circle of the 56 Aubrey holes. An earthwork, called Avenue, along which the Heel Stone was located. Phase II ( BC): Aubrey holes partially filled, wooden settings in the center and at the eastern entrance. Phase III ( BC): a circle of Sarsens within a horseshoe- shaped arrangement of Trilithons and four great stones as stations. 3

6 Stonehenge alignments Heel Stone 4

7 A.Aveni, Tropical Astronomy, Science 1981 The Caracol: Maya observatory (Chichén Itzá, Yucatan-Mexico) viewing shaft These windows align with some astronomical sightlines: Venus rising at its northernmost southernmost positions, as well as the equinox sunset 5

8 A.Aveni, Tropical Astronomy, Science 1981 The Caracol: Maya observatory (Chichén Itzá, Yucatan-Mexico) viewing shaft These windows align with some astronomical sightlines: Venus rising at its northernmost southernmost positions, as well as the equinox sunset Since Venus’s orbit is tilted 4º with respect to the ecliptic, its position shifts against the horizon, the northernmost and the southernmost positions correspond to the farthest northern and southern points above the celestial equator. 5

9 N. Strobel, Astronomy without a telescope The Caracol: Maya observatory (Chichén Itzá, Yucatan-Mexico) These windows align with some astronomical sightlines: Venus rising at its northernmost southernmost positions, as well as the equinox sunset Since Venus’s orbit is tilted 4º with respect to the ecliptic, its position shifts against the horizon, the northernmost and the southernmost positions correspond to the farthest northern and southern points above the celestial equator. 5

10 Staircase almost perfect match with Venus setting at its northernmost position The building diagonal is aligned with winter and summer solstices The Caracol: Maya observatory (Chichén Itzá, Yucatan-Mexico) 5

11 El Castillo: Pyramid of Kukulkán (Chichén Itzá, Yucatan-Mexico) 1. At the equinox sunsets, a play of light and shadow creates the appearance of a snake that gradually undulates down the stairway of the pyramid. 6

12 El Castillo: Pyramid of Kukulkán (Chichén Itzá, Yucatan-Mexico) 1. At the equinox sunsets, a play of light and shadow creates the appearance of a snake that gradually undulates down the stairway of the pyramid. this sinuous shadow joins with one of the snake-head sculpture carved into the base of the monument 6

13 El Castillo: Pyramid of Kukulkán (Chichén Itzá, Yucatan-Mexico) 1. At the equinox sunsets, a play of light and shadow creates the appearance of a snake that gradually undulates down the stairway of the pyramid. this sinuous shadow joins with one of the snake-head sculpture carved into the base of the monument 2. It was used as calendar: each of the 4 stairways has 91 steps + 1 step on the top = 365 steps 6

14 El Castillo: Pyramid of Kukulkán (Chichén Itzá, Yucatan-Mexico) 1. At the equinox sunsets, a play of light and shadow creates the appearance of a snake that gradually undulates down the stairway of the pyramid. this sinuous shadow joins with one of the snake-head sculpture carved into the base of the monument 2. It was used as calendar: each of the 4 stairways has 91 steps + 1 step on the top = 365 steps 3. the west plane faces the zenith passage with a precision within 1º 6

15 Modern (day) Maya (day) Lunar period Solar period Mars period Venus period Maya astronomy From this information, they developed calendars to Keep track of celestial movements: their solar calendar was more precise than the present Gregorian calendar. Maya were skilled observers of the sky: they calculated the complex motions of the Sun, the stars and planets and recorded this information in their codices (“Dresden Codex”). 9 Venus had been recognized as morning and evening star! Greek astronomers had recorded Venus as two different stars.

16 Skywatchers Venus: morning and evening star Venus is an inferior planet: it has phases as the Moon Inferior conjunction Superior conjunction Dresden Codex (day) Modern (day) Morning star (after heliacal rise) Invisible (superior conjunction) 9050 Evening star Invisible (inferior conjunction) 88 Total584 8 Heliacal rise=Sun and Venus rise together. After heliacal rise, Venus rises before the sunrise: morning star. After superior conjunction, Venus rises after the sunrise, so set after the sunset: evening star.

17 Modern (day) Maya (day) Lunar period Solar period Mars period Venus period Maya astronomy From this information, they developed calendars to keep track of celestial movements: their solar calendar was more precise than the present Gregorian calendar. Maya were skilled observers of the sky: they calculated the complex motions of the Sun, the stars and planets and recorded this information in their codices (“Dresden Codex”). 7 It seems incredible! But we have forgotten what can be achieve by careful naked eye observation using simple instruments.

18 Marking time without instruments Gnomons, simple long sticks located on a plate, were already used by Greek astronomers. To determine the solstice day is rather easy only by studying shadows: at summer solstice the Sun is at its highest point and the shadows it casts are the shortest; vice versa at winter solstice. At the beginning, gnomons were used as sundials (by dividing the plate into equal intervals), as well as to establish cardinal directions (south=the position of the shortest shadow of a day) and as calendar (by dividing the period between two solstices into intervals, each of one characterized by a particular shadow length) Maya used the zenith passage which are characterized by shadowless moments as reference day. 11 no thickness gnomon

19 The zenith-horizon system At temperate zones, the observer views circulatory motion. In this case it is simpler using the celestial pole and the celestial equator as reference lines. The horizon functions as fundamental reference line, together with the zenith. Here star motion is vertical. The sun can be observed at zenith at the equinoxes. Tropics are the maximum latitudes at which the Sun can be observed at zenith: ZENITH PASSAGES. 10 N. Strobel, Astronomy without a telescope

20 Zenith Tubes There is no evidence that gnomons were used by Maya, but they used “zenith tubes” to identify the shadowless moment. These tubes admit the Sun’s image to pass vertically into a darkness chamber A.Aveni, Tropical Astronomy, Science (1981) At the ruins of Xochicalco, Mexico, a 8 m long perfect straight tube, which opens into a roundish chamber (10 m diameter), was found. The cross section of this tube is hexagonal with a 2.5º of FOV. 12

21 Sun-Moon angle 0º (new phase) SOLAR ECLIPSE Sun-Moon angle 180º (full phase) LUNAR ECLIPSE When an eclipse occurs? AND Moon at the line of nodes intersection of the Moon’s orbit with the ecliptic twice a year at different dates Moon’s orbit precesses 13

22 Stonehenge: an eclipse predictor only when, not where G. Hawkins, The Stonehenge Decoded, Nature 1963 Full moon markers

23 Stonehenge: an eclipse predictor only when, not where G. Hawkins, The Stonehenge Decoded, Nature 1963 Full moon markers 56 a perfect number! 56/2=28 Moon’s orbit is days Moon marker – twice a day and skip one each cycle

24 Stonehenge: an eclipse predictor only when, not where G. Hawkins, The Stonehenge Decoded, Nature 1963 Full moon markers 56 a perfect number! 56/2=28 Moon’s orbit is days Moon marker – twice a day and skip one each cycle 56*6.5=364 Earth’s orbit is days Sun marker – every 6.5 days and during solstices half more

25 Stonehenge: an eclipse predictor only when, not where G. Hawkins, The Stonehenge Decoded, Nature 1963 Full moon markers 56 a perfect number! 56/2=28 Moon’s orbit is days Moon marker – twice a day and skip one each cycle 56*6.5=364 Earth’s orbit is days Sun marker – every 6.5 days and during solstices half more 56/3=18.66 Orbit of Nodes is y Node markers – every four months

26 Stonehenge: an eclipse predictor only when, not where G. Hawkins, The Stonehenge Decoded, Nature 1963 Full moon markers Solar eclipse: Moon, Sun and a node in the same position Lunar eclipse: the Sun and a node opposite to the Moon and the other node

27 Conclusions Ancient astronomers were surely skilled sky observers They knew the precise cycle of many celestial objects, they were able to predict important astronomical events such as eclipses. This whole knowledge had been obtained without any modern instruments. If this appear us incredible is only because we are no more accustomed to take simple measurements. It is not necessary to invoke the help of gods coming from the tenth planet of the solar system! (A. Alford, Gods of the new millennium) Astronomical knowledge in ancient cultures was used for religious (to time rituals, to decide where to build a temple) and civil purposes (when to sow and harvest) Ethnological implications. They were not interested in accuracy! We should remember this difference with the modern science. 15

28 THE END

29 Backup Slides

30 When the gnomon has a finite thickness, there will be two dial centers and double noon lines. The double noon lines are spaced a distance equal to the thickness of the gnomon and this space is known as the noon gap.

31 Precession of Moon

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