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1 ARCHAEOASTRONOMY Thursday meeting – January 25 2007 Roberta Zanin

Dec 28, 2015

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  • ARCHAEOASTRONOMYThursday meeting January 25 2007Roberta Zanin

  • Archaeoastronomy: the study of the practiceof 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 alignmentsassociated with ancient architecture. (Hawkins, 1966)

    History of Astronomy: it is concerned withacquisition of precise knowledge by ancient cultures.(Crowe and Down, 1999)

    Ethnoastronomy: a branch of cultural anthropologythat develops an understanding of cultural behavioras gleaned from indigenous perceptions of events inthe heaven. (Fabian, 2001)1

  • OutlineAstroarchaeonomy two examples of building alignments:Stonehenge Chichn Izt (Mexico), the Caracol and El Castilloas proof of the perfect astronomical knowledge of these two ancient cultures.

    History of astronomyhow this knowledge could be obtained without any modern instruments1. how to predict an eclipse 2. how to measure the cycle of celestial bodies

    Conclusions Ethnoastronomy2

  • StonehengePhase I (2950-2900 BC): a circular bank with a ditch, inside thebank a circle of the 56 Aubrey holes.An earthwork, called Avenue, along which the Heel Stone was located.Phase II (2900-2400 BC):Aubrey holes partially filled, woodensettings in the center and at theeastern entrance.Phase III (2550-1600 BC):a circle of Sarsens within a horseshoe-shaped arrangement of Trilithonsand four great stones as stations. 3

  • StonehengePhase I (2950-2900 BC): a circular bank with a ditch, inside thebank a circle of the 56 Aubrey holes.An earthwork, called Avenue, along which the Heel Stone was located.Phase II (2900-2400 BC):Aubrey holes partially filled, woodensettings in the center and at theeastern entrance.Phase III (2550-1600 BC):a circle of Sarsens within a horseshoe-shaped arrangement of Trilithonsand four great stones as stations. 3

  • Stonehenge alignments Heel Stone4

  • A.Aveni, Tropical Astronomy, Science 1981The Caracol: Maya observatory(Chichn Itz, Yucatan-Mexico)viewing shaftThese windows align with someastronomical sightlines:

    Venus rising at its northernmost southernmost positions, as well as the equinox sunset 5

  • A.Aveni, Tropical Astronomy, Science 1981The Caracol: Maya observatory(Chichn Itz, Yucatan-Mexico)viewing shaftThese windows align with someastronomical sightlines:

    Venus rising at its northernmost southernmost positions, as well as the equinox sunset Since Venuss orbit is tilted 4 with respect to the ecliptic, its position shifts against the horizon, the northernmost and thesouthernmost positions correspond to the farthest northern and southernpoints above the celestial equator.

    5

  • N. Strobel, Astronomy without a telescopeThe Caracol: Maya observatory(Chichn Itz, Yucatan-Mexico)These windows align with someastronomical sightlines:

    Venus rising at its northernmost southernmost positions, as well as the equinox sunset Since Venuss orbit is tilted 4 with respect to the ecliptic, its position shifts against the horizon, the northernmost and thesouthernmost positions correspond to the farthest northern and southernpoints above the celestial equator.

    5

  • Staircase almost perfect match with Venus settingat its northernmost positionThe building diagonal is aligned with winter and summer solstices The Caracol: Maya observatory(Chichn Itz, Yucatan-Mexico)5

  • El Castillo: Pyramid of Kukulkn (Chichn Itz, 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

  • El Castillo: Pyramid of Kukulkn (Chichn Itz, 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-headsculpture carved into the baseof the monument6

  • El Castillo: Pyramid of Kukulkn (Chichn Itz, 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-headsculpture carved into the baseof the monument2. It was used as calendar:each of the 4 stairways has 91 steps + 1 step on the top = 365 steps 6

  • El Castillo: Pyramid of Kukulkn (Chichn Itz, 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-headsculpture carved into the baseof the monument2. 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 aprecision within 16

  • Maya astronomyFrom 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).9Venus had been recognized asmorning and evening star!

    Greek astronomers had recordedVenus as two different stars.

  • SkywatchersVenus: morning and evening star Venus is an inferior planet:it has phases as the Moon Inferior conjunctionSuperiorconjunction8Heliacal rise=Sun and Venus rise together.After heliacal rise, Venus rises before thesunrise: morning star.After superior conjunction, Venus risesafter the sunrise, so set after the sunset: evening star.

  • Maya astronomyFrom this information, they developed calendars to keeptrack 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).7It seems incredible!

    Butwe have forgotten what can beachieve by careful naked eye observation using simpleinstruments.

  • Marking time without instrumentsGnomons, 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 betweentwo 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.11no thickness gnomon

  • The zenith-horizon system At temperate zones, the observerviews circulatory motion. In this caseit is simpler using the celestial poleand the celestial equator as referencelines. The horizon functions as fundamental reference line, together with the zenith.Here star motion is vertical. The sun can be observed at zenithat the equinoxes.Tropics are the maximum latitudes at which the Sun can be observed at zenith: ZENITH PASSAGES. 10N. Strobel, Astronomy without a telescope

  • Zenith TubesThere is no evidence that gnomons were used by Maya, but they used zenith tubesto identify the shadowless moment.

    These tubes admit the Suns 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 2.5 of FOV.12

  • Sun-Moon angle 0(new phase)SOLAR ECLIPSE

    Sun-Moon angle 180(full phase)LUNAR ECLIPSEWhen an eclipse occurs?AND Moon at the line of nodes intersection of the Moons orbit with the ecliptic twice a year at different datesMoons orbit precesses13

  • Stonehenge: an eclipse predictoronly when, not whereG. Hawkins, The Stonehenge Decoded, Nature 1963Full moon14+4markers

  • Stonehenge: an eclipse predictoronly when, not whereG. Hawkins, The Stonehenge Decoded, Nature 1963Full moon14+4markers56 a perfect number!

    56/2=28 Moons orbit is 27.322daysMoon marker twice a dayand skip one each cycle

  • Stonehenge: an eclipse predictoronly when, not whereG. Hawkins, The Stonehenge Decoded, Nature 1963Full moon14+4markers56 a perfect number!

    56/2=28 Moons orbit is 27.322daysMoon marker twice a dayand skip one each cycle56*6.5=364Earths orbit is 365.25 daysSun marker every 6.5 daysand during solstices half more

  • Stonehenge: an eclipse predictoronly when, not whereG. Hawkins, The Stonehenge Decoded, Nature 1963Full moon14+4markers56 a perfect number!

    56/2=28 Moons orbit is 27.322daysMoon marker twice a dayand skip one each cycle56*6.5=364Earths orbit is 365.25 daysSun marker every 6.5 daysand during solstices half more56/3=18.66Orbit of Nodes is 18.61 yNode markers every four months

  • Stonehenge: an eclipse predictoronly when, not whereG. Hawkins, The Stonehenge Decoded, Nature 1963Full moon14+4markersSolar eclipse:Moon, Sun and a nodein the same position

    Lunar eclipse:the Sun and a node oppositeto the Moon and the othernode

  • Conclusions Ancient astronomers were surely skilled sky observersThey knew the precise cycle of many celestial objects, they were able to predict important astronomical events such as eclipses. This whole