How to read the atlas
Time runs left → right (1200 BCE → 1600 CE, linear, labelled every 250 years with lighter century lines). Vertical rows are cultures and regions — the Olmec, the Late Preclassic Long Count centres, Zapotec Monte Albán, Teotihuacan and central Mexico, the Classic and Postclassic Maya, and the Aztec — plus a bottom row for contact and survival. Each glyph sits at its event's date on its row; the bars are sites, codices, and monuments, showing the period each was in use.
There are no transmission lines: Mesoamerica developed without contact with the Old World. The single dashed red line at 1519 marks the arrival of the Spanish. Dates are Common Era on the axis; for entries within the Long Count era each card also gives the approximate Long Count (baktun.katun.tun), the day-count the Maya reckoned from a base in 3114 BCE.
Glyph shape is the kind of entry: filled circle = observation or reckoning, open circle = codex or inscribed record, square = founding of a centre, triangle = building or instrument, diamond = contact or political event. Glyph fill colour matches the culture stripe.
The cultures, briefly
Three things that set Mesoamerican astronomy apart
The first is the double calendar. Every Mesoamerican culture kept two interlocking cycles: a 260-day sacred count (the Maya tzolkʼin, the Aztec tōnalpōhualli) and a 365-day year (the haabʼ / xiuhpōhualli). Together they name each day uniquely within a 52-year Calendar Round. The Maya added the Long Count, an absolute day-count that fixes any date within a span of millennia — a chronological precision matched nowhere else in the pre-modern world.
The second is horizon astronomy. With no armillary spheres or graduated instruments, Mesoamerican observers worked from the horizon: they oriented buildings to the rising or setting sun on significant days, watched the twice-yearly passage of the sun through the zenith at tropical latitudes, and tracked Venus and the Pleiades against the skyline. The instruments are the buildings themselves.
The third is the Venus and eclipse tables. The Dresden Codex contains a table of the 584-day cycle of Venus, corrected to stay accurate over centuries, and an eclipse-warning table spanning 33 years — sustained, quantitative astronomy preserved in one of the four Maya books to survive the conquest.
Methodology — what counts, what does not
Inclusion. An entry qualifies if (a) it belongs to the Mesoamerican tradition between roughly 1200 BCE and the mid-sixteenth century, and (b) it is a primary contribution to calendar, orientation, or sky-observation — a dated monument, an aligned building, a codex table, or a documented practice. Because the tradition is material rather than textual, buildings and monuments carry much of the evidence.
Anonymous by nature. Mesoamerican astronomy has almost no named practitioners; the work was done by calendar priests and day-keepers whose names were not recorded. This volume therefore departs from the others: the bars and the gallery are sites, codices, and monuments rather than people, and the “biography” card describes the object and its astronomy.
Sources and dating. Entries cite a primary artifact — an inscribed Long Count date, a codex page, a building alignment — or a modern study in archaeoastronomy or epigraphy (Aveni, Milbrath, the Maya Codices literature). Calendar correlations use the standard GMT (Goodman–Martínez–Thompson) constant. Alignment claims vary in strength; the card indicates where an interpretation is contested.
Caution. Archaeoastronomy invites over-reading — it is easy to find an alignment by chance. The atlas favours cases supported by repetition across sites, by ethnohistoric testimony, or by an explicit record (as in the Dresden tables), and flags the more speculative claims rather than presenting them as settled.
Companion RAVEN material
The Dresden Codex Venus table is one of the clearest pre-telescopic records of a planet's synodic cycle, and sits alongside the Babylonian and other early planetary records referenced in the RAVEN Foundations. The zenith-passage and horizon-calendar methods — astronomy done entirely by orientation and the naked eye — are the low-technology end of the observing-methods spectrum traced in the Platforms Atlas. Unlike the other five volumes, this tradition connects to none of them directly: it is the control case, a full astronomy developed in isolation, and is best read as a demonstration of how much of the sky can be recovered from the horizon and a count of days.