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1 ARCHAEOASTRONOMY Roberta Zanin
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Page 1: Astro arqueología

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ARCHAEOASTRONOMY

Roberta Zanin

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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

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Outline• Astroarchaeonomy two examples of building alignments:1. Stonehenge 2. Chichén Iztá (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

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Stonehenge• Phase 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 Trilithons

and four great stones as stations.

3

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Stonehenge• Phase 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 Trilithons

and four great stones as stations.

3

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Stonehenge alignments Heel Stone

4

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A.Aveni, Tropical Astronomy, Science 1981

The Caracol: Maya observatory(Chichén Itzá, Yucatan-Mexico)

viewing shaft

These windows align with someastronomical sightlines:

Venus rising at its northernmost southernmost positions,

as well as the equinox sunset

5

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A.Aveni, Tropical Astronomy, Science 1981

The Caracol: Maya observatory(Chichén Itzá, Yucatan-Mexico)

viewing shaft

These windows align with someastronomical 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 thesouthernmost positions correspond

to the farthest northern and southernpoints above the celestial equator.

5

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9N. Strobel, Astronomy without a telescope

The Caracol: Maya observatory(Chichén Itzá, Yucatan-Mexico)

These windows align with someastronomical 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 thesouthernmost positions correspond

to the farthest northern and southernpoints above the celestial equator.

5

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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

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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

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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 baseof the monument

6

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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 baseof the monument

2. It was used as calendar:each of the 4 stairways has 91 steps + 1 step on the top = 365 steps 6

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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 baseof 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 1º6

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Modern(day)

Maya(day)

Lunar period

29.53059 29.53086

Solar period

365.2420 365.2466

Mars period

779.94 780

Venus period

583.93 583.9203

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”).

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Venus had been recognized asmorning and evening star!

Greek astronomers had recordedVenus as two different stars.

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Venus: morning and evening star Venus is an inferior planet:it has phases as the Moon

Inferior conjunction

Superiorconjunction

Dresden

Codex(day)

Modern

(day)

Morning star(after heliacal

rise)

236 263

Invisible(superior

conjunction)

90 50

Evening star 250 263

Invisible(inferior

conjunction)

8 8

Total 584 584 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.

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Modern(day)

Maya(day)

Lunar period

29.53059 29.53086

Solar period

365.2420 365.2466

Mars period

779.94 780

Venus period

583.93 583.9203

Maya astronomy

From 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”).

7

It seems incredible!

Butwe have forgotten what can be

achieve by careful naked eye observation using simple

instruments.

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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.

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no thickness gnomon

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The zenith-horizon system

At temperate zones, the observerviews circulatory motion. In this caseit is simpler using the celestial pole

and 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 zenith

at the equinoxes.

Tropics are the maximum latitudes at which the Sun can be observed at zenith: ZENITH PASSAGES.

10N. Strobel, Astronomy without a telescope

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Zenith TubesThere 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.

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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

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Stonehenge: an eclipse predictor

only when, not where

G. Hawkins, The Stonehenge Decoded, Nature 1963

Full moon

14

+

4markers

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Stonehenge: an eclipse predictor

only when, not where

G. Hawkins, The Stonehenge Decoded, Nature 1963

Full moon

14

+

4markers

56 a perfect number!

56/2=28 Moon’s orbit is 27.322days

Moon marker – twice a dayand skip one each cycle

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Stonehenge: an eclipse predictor

only when, not where

G. Hawkins, The Stonehenge Decoded, Nature 1963

Full moon

14

+

4markers

56 a perfect number!

56/2=28 Moon’s orbit is 27.322days

Moon marker – twice a dayand skip one each cycle

56*6.5=364Earth’s orbit is 365.25 days

Sun marker – every 6.5 daysand during solstices half more

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Stonehenge: an eclipse predictor

only when, not where

G. Hawkins, The Stonehenge Decoded, Nature 1963

Full moon

14

+

4markers

56 a perfect number!

56/2=28 Moon’s orbit is 27.322days

Moon marker – twice a dayand skip one each cycle

56*6.5=364Earth’s orbit is 365.25 days

Sun marker – every 6.5 daysand during solstices half more

56/3=18.66Orbit of Nodes is 18.61 y

Node markers – every four months

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Stonehenge: an eclipse predictor

only when, not where

G. Hawkins, The Stonehenge Decoded, Nature 1963

Full moon

14

+

4markers

Solar eclipse:Moon, Sun and a nodein the same position

Lunar eclipse:the Sun and a node opposite

to the Moon and the othernode

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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 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 withthe modern science.

15

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THE END

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Backup Slides

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When the gnomon has a finite thickness, there will betwo 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.

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Precession of Moon

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