and the Astronomers of Yore

Changes in the Sky

Simulating the current night sky is easy to do with a star chart or planisphere, which accounts for the time, date, and geographic latitude. But these charts don't work for ancient cultures, because of precession. To go back in time, archaeoastronomers and teachers can turn to personal computers and any of a number of software packages. The shareware Skyglobe operates on IBM-compatible computers; the ASP sells Dance of the Planets (IBM) and Voyager II (Mac) through its catalog. Such simulations can be used to study ethnic groups of the past. For example:

• The simultaneous appearance of the Sun and star Sirius on the horizon, in the middle of the third millennium B.C. as seen from Giza, Egypt. When Sirius, in the constellation of Canis Major, appeared on the horizon at the same time as the Sun, the Egyptians knew it was the summer solstice. This marked the time when the Nile flooded. The silt deposited by the overflowing Nile was important to Egyptian agriculture.
• The merger of the images of the planets Venus and Jupiter on June 16, 2 B.C., as seen from Bethlehem, Palestine. This merger is a possible interpretation of the Star of Bethlehem.
• The appearance of the Crab supernova during July 1054, as seen from Beijing, China, just before sunrise, with the crescent Moon and the planet Mercury nearby. The supernova was considerably brighter than Venus, but probably not as bright as the full Moon.
• The simultaneous appearance of the Sun and the Pleiades near the horizon as seen from Teotihuacan, Mexico, about two millennia ago. The Pleiades is a small cluster of stars in the constellation of Taurus, and the date corresponds to one of the times the Sun passed through the zenith.

Messages on a Hillside

People did not just watch the sky; they evidently tried to communicate to it. The large earthen figures of the British Isles and Peru are huge and difficult to recognize from the ground; perhaps they were constructed for viewing by the gods. Examples include the Long Man of Wilmington, England and the Owl Man of Peru (see figure 8 and figure 9). Although the true intentions of the people who constructed the figures is still a mystery, students can make informed guesses by comparing the figures to images intended by modern scientists for extraterrestrial civilizations.

Figure 8 Long Man of Wilmington, England.	Figure 9 Owl Man of Peru.

Examples of modern messages include:

• Radio signals beamed toward the globular star cluster M13 in the constellation of Hercules, with the large radio dish at Arecibo, Puerto Rico [see "The Search for Extraterrestrial Intelligence,'' The Universe in the Classroom, Spring 1992].
• The plaque fixed to the Pioneer spaceprobe (see figure 10).
• Encapsulated photographs placed in the interplanetary vehicle Voyager (now available on the CD-ROM Murmurs of Earth).

Students can tabulate and analyze the striking similarities that exist among the modern and ancient images. They could also construct an original pictorial message for extraterrestrial civilizations, explaining why they chose particular symbols. If a nearby football field is nearby, students can map their picture on graph paper and lay it out on the ground.

Figure 10 The Pioneer plaque, designed as a message to extraterrestrial beings. The plaque shows where Pioneer came from and who sent it. The barbell at top left represents the hydrogen atom; the radial pattern at left center shows the position of the Earth with respect to pulsing stars. Photo courtesy of NASA.

Deciphering the unique number system of the Maya is another archaeoastronomy topic that involves a minimum of math. Unlike our modern Arabic system -- 10 digits, strung out horizontally, representing powers of 10 -- the Maya used digits, stacked vertically, representing powers of 20 (see figure 11). Several collections of early writing of the Maya survive; numbers from them can be read and in some cases interpreted (see figure 12). One document, for example, shows the 584-day synodic period of Venus and the associated Maya god, Kukulcan [see "Ancient Astronomy in Mexico and Central America,'' Mercury, January/February 1975, p. 24; "Emissaries to the Stars: The Astronomers of Ancient Maya,'' Mercury, January/February 1995, p. 15]. The synodic period of revolution of a planet is the length of time it takes to return to the same position relative to the Sun, as seen from Earth.

Figure 11 Mayan numerals. A dot means 1, a horizontal bar means 5. These symbols are an abstraction of hand-counting gestures from pre- literate times. The Mayas used base-20 notation, as opposed to our base-10 notation; each Mayan numeral represents a number from 1 to 19. The numerals can be written either horizontally or vertically; the dots appear above or to the left of the bars. The Maya often decorated their numerals and adopted special glyphs for important numbers.

As archaeoastronomers study the calendar of the Maya, they find ceremonial intervals of time that can be related to the year and the synodic period of Venus. These cycles are represented by large, whole numbers; when multiplied by other cosmologically significant whole numbers, they result in a single, very large, sacred number, 37,960.

Figure 12 The Maya Eclipse Table, from the Dresden Codex. There are plenty of numbers to decipher! For example, the arrow points to a number that consists of two numerals. The top numeral, three dots and a bar, equals 8. The bottom numeral, two dots and three bars, equals 17. Since the Mayas used base-20 notation, this number is 8 x 20 + 17 = 177. The number 177 was important in eclipse predictions. Photo courtesy of G. Kohlmann and L. Blanco, CIEA del Instituto Politecnico Nacional, Mexico.

The archaeoastronomy of numerous societies over the millennia shows remarkable similarities and differences in the interpretation of the appearance and motions of the celestial bodies. Worldwide similarities are mostly in timekeeping and the association of a hereafter life with the heavens. The differences are mostly in the ways and times that particular holidays were determined.

In spite of the ancient origin of the diverse ethnic topics of archaeoastronomy, the subject is quite contemporary in character. As the world shrinks with advances in technology of communications and travel, the more we are required to understand the global community and its ethnic diversity.

LOUIS WINKLER teaches astronomy to nonscience students at Pennsylvania State University in University Park. His instruction includes large lectures with numerous computer demonstrations, small laboratories with students operating computers in many activities, and a mathematically founded course in archaeoastronomy.

Archaeoastronomy Resources

• Archaeoastronomy / A Science Module for High School and Conscience College Students / Text and Activities. Includes Harvard Graphics and a teacher's manual, 51 pages, $39.95.
• Skyglobe Activities. Detailed instructions for simulating skies for different times and latitudes, 6 pages, $9.95.
• Popular Archaeoastronomy. Used in a college level course, hand drawn sketches, 220 pages, $34.95.

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