Although Maya builders possessed many practical skills, the most distinctive Maya achievements were in abstract mathematics and astronomy. One of their greatest intellectual achievements was a pair of interlocking calendars, which was used for such purposes as the scheduling of ceremonies. One calendar was based on the sun and contained 365 days. The second was a sacred 260-day almanac used for finding lucky and unlucky days. The designation of any day included the day name and number from both the solar calendar and the sacred almanac. The two calendars can be thought of as two geared wheels that meshed together at one point along the rim, with the glyphs for the days of the sun calendar on one wheel and the glyphs for the days of the sacred almanac on the other. With each new day the wheels were turned by one gear. The name for each day was formed by combining the name for the sun calendar day with the name for the sacred almanac day.
Maya astronomers could make difficult calculations, such as finding the day of the week of a particular calendar date many thousands of years in the past or in the future. They also used the concept of zero, an extremely advanced mathematical concept. Although they had neither decimals nor fractions, they made accurate astronomical measurements by dropping or adding days to their calendar. For example, during 1000 years of observing the revolution of the planet Venus, which is completed in 583.92 days, Maya astronomers calculated the time of the Venusian year as 584 days. The Maya method of reckoning time involved counting forward from a hypothetical fixed point and expressing the date in time periods based on the number 20 and counted in intervals of 1, 20, 360, 7200, and 144,000 days. Such dates appear on carved stone monuments dating to as early as the late Preclassic period, and they are prevalent throughout the lowlands on monuments from the Classic period.
The Maya developed a complex system of hieroglyphic writing to record not only astronomical observations and calendrical calculations, but also historical and genealogical information. Many recent advances have occurred in the decipherment of the Mayan script. These breakthroughs made it possible to conclude that Mayan hieroglyphs were a mixture of glyphs that represent complete words and glyphs that represent sounds, which were combined to form complete words. Scribes carved hieroglyphs on stone stelae, altars, wooden lintels, and roof beams, or painted them on ceramic vessels and in books made of bark paper. Discoveries reported early in 2006 indicate that the Maya were writing more than 2,300 years ago, at least 600 years earlier than previously thought.