Chichen Itza

Shadow of the Equinox

The cycle of the sun and how it interacts with the pyramid at Chichen Itza.

The Mayans succeeded in an almost impossible mission with the completion of their structures at Chichen Itza. A poetic combination of form, style, function, religion, philosophy, mathematics and geometry. A true symbiosis of all of their intelligence and art in one location, to be studied and admired by all that visit. By far the most impressive aspect of the Pyramid of Kukulcan is it's relationship with the sun and how it reflects the equinoxes and solstices of our solar year with stunning accuracy. Before one can fully understand the workings of the Shadow of the Equinox, a few basics on astronomy need to be reviewed.

An equinox occurs twice each year when our sun, in its orbit around the earth in a fashion unique to these times of the year, passes directly over the Earth's equator and the length of the daylight and evening hours is equal. Hence the word equinox is derived from the Latin for "equal" aequus, and nox meaning "night". The spring equinox occurs on March 21. Six months later, on Sept 22, we have the Fall Equinox. The summer solstice occurs on June 21st. On this day earth sees the longest duration of daylight. Six months later is the winter solstice on December 22, when we see the shortest daylight and the longest night of the year. On these days the sun almost seems to pause in its orbit before resuming its course, and it is why the word solstice is based on the Latin sol, for "sun", and sistere or "to cause to stand". This cycle then repeats itself as the Earth continues to rotate around the sun. It is interesting to note that there are exactly 91 days between each of these events, and 92 days between the June 21 summer solstice and the September 21 equinox. This adds up to a 365 day solar year with the 91 days between each event matching the 91 steps to each side of the pyramid (described here).

Each of these solar events, the two solstices and the two equinoxes, can be measured and predicted using the patterns of light and shadow that fall on El Castillo at various times of the year. It is believed that the Mayans used the various shadows and designs formed by the Pyramid to signal the beginning of a harvest or of a planting, to predict the best dates to be married or to be buried, and for other various ceremonial reasons. The cycles of the sun also play out to another Mayan tradition of the number 52. To us, it is a coincidence that this is the number of weeks in our standard year. But to the Maya it represented, in years, the time of one "cycle".

What follows below is a hypothesis of how the the location for the pyramid was derived:.

Image descriptionThe Mayan astronomer stood out in a clearing and marked a circle equal to the outer dimension of the finished structure. He indicated a point that was the absolute center of the circle.

Image descriptionOn the one day he knew had the longest amount of daylight in the year, he then observed the position of the sun at sunrise and at sunset, and marked the outer rim of the circle where the line of the sun crossed it at both times to give the following diagram. These are the positions of the sun on the summer solstice.

Image descriptionThe astronomer then waited for the exact number of days between the cycles, and six months later on the day of the winter solstice he repeated his earlier observations of the sun at sunrise and sunset and marked his line of site with the sun on the outer rim of the circle.

Image descriptionConnecting lines could then be drawn across the diameter of the circle that connected the points indicating the line of vision of the sun on the two solstices each year..

Image descriptionRight angles could then be drawn corresponding to the dimensions of the final structure (and the same as the diameter of the original circle) "pointing" to the position of the sun at the two solstices.

Image descriptionThe square dimensions of the base of the pyramid could then be mapped on the ground. This diagram also shows the position of the sun on the days of the equinox when day and night are of equal length. The North-Eastern most "point" is tilted exactly 18 degrees from true north.

Image descriptionThe final structure is then built from this design. As mentioned above, the final design also incorporates significant calculations related to the sun and the length of the Mayan calendar year such as the 91 steps on each side of the pyramid (and one common on the top) equaling the same number of stairs as there are days in a solar year.

Image descriptionThis diagram shows the position of the sun during sunset on the winter solstice. This is the day when the Southern and Western faces of the pyramid are bathed in the shortest amount of daylight for the year. This is in opposition to June 21 on the summer solstice, when the Northern and Eastern faces are in the sunlight for the longest time of the year. On these days the pyramid is exactly half covered with shadow or light.

Image descriptionThis diagram shows the position of the sun at sunset on the day of the Fall equinox (Sept 22nd) The alignment of the sun and the way that it reflects and shadows the tiers, or layers of the pyramid are what causes the phenomenon known as the Seven Triangles of Light and Shadow to appear on the northern staircase.

The Mayan Calendar began on on the first day of Pop month, or our July sixteenth. They kept a count of fifty two days (breaking down into two months with twenty days each, two weeks with five days each, and two additional days. This count puts us in the twelfth day of the third month called Sip, or September sixth by our calendar. This was the day the Mayans held their most significant ceremonies at the base of the pyramid as September sixth (as well as April sixth) is when the complete nine triangles of shadow and light can be seen on the western side of the north staircase. Nine triangles being the most complete example of the phenomenon, with eight visible on the staircase and the ninth illuminating the head of Kukulkan. From the twelfth day of Sip (or September sixth) count foreword three weeks (Mayan weeks with five days in each) and one additional day (Sixteen days total) and we arrive at the ninth day in the fourth month Zoodz (Or September twenty second) on this date there are seven triangles on the same side of the main staircase which indicated to the Mayan astronomers that the Earth had completed its cycle around the sun. Two of the triangles seen on September sixth completely shift off the pyramid and are projected onto the ground at the floor of the staircase. On the sixth day in the month of Tseek (October ninth or seventeen days after September twenty second) there are six triangles visible.

There are several dates and variations of the shadows and triangles as the sun approached the positions for which the pyramid was built. They all had varying degrees of significance within the Mayan culture and I have only focused on the "main" ones.

El Castillo Around the Year

July 16Start of Mayan new year. Add 52 days to this date (the same as the number of years in Maya "cycle" and you arrive at Sept 6th
Sept 6All nine triangles of light are visible between 5 and 5:30 PM.
Sept 22Fall equinox (Day and night equal length) when seven triangles are visible. This is 92 days from previous summer solstice of June 21.
Oct 9Six triangles visible between 4 and 4:30 PM.
Dec 21Winter solstice, longest night of the year. (91 days from Sept 22 fall equinox) North and East sides in total darkness while West and South are in daylight. 91 Days from fall equinox
March 5Six triangles visible between 4 and 4:30 PM.
March 21Spring Equinox. (Day and night equal length) Seven triangles between 4:30 - 5 PM. 91 days (same as stairs on the pyramid) from December 21 solstice.
April 6Nine triangles between 5 and 5:30 PM All possible triangles visible at this time.
June 21Summer solstice. Longest day of the year. (91 days from the March 21 show of seven triangles) South and West sides in total darkness between 7 and 7:30 AM.

-- Chris Reeves