Solar Zenith

It may be the latitude of my country of birth that gives me such an interest in the skies of Guatemala. How different the skies can look in the tropics is almost inconceivable. I am originally from 52^o North. Having been a skywatcher since I was young, I was used to seeing Orion standing proudly in the winter sky. Now, having lived in Guatemala for 16 years, I am accustomed to seeing him reclining as if in a hammock. It was in Guatemala that I was able to see Mercury clearly for the first time, with the inclination of the ecliptic giving sufficient altitude above the horizon to evade the Sun’s glare.

However, the solar zenith transit is a more unique experience, one that is alien to my birth country. This transit is, of course, what defines the latitude of the tropics. The sun reaches a zenith angle of 90^o at solar noon. Solar noon could be defined as the point where the sun is at 90^o on the ecliptic, the path that it follows through the sky each day. Whilst this would be thought to be 12:00 pm, the exact location and time of year within a time zone will change this slightly. For instance, in my case, solar noon in San Pablo la Laguna can vary between 12:02 pm and 12:19 pm.

On the equator, the solar zenith angle reaches 90^o on the equinoxes, therefore twice per year. On the Tropic of Cancer, the Sun will reach 90^o on only one occasion, the June solstice, and on the Tropic of Capricorn on the December solstice. As we travel from the equator to the Tropic of Cancer, the solar zenith dates change, becoming closer together from the equinox dates towards the June solstice.

Calendar Connection

Of course, what intrigued me, living here in the Maya lands, are the dates of the solar zenith transits here at 14°44’N / 91°17’W. The solar zenith tends to fall on April 29^th and August 12^th. If one is earlier, so is the other, preserving 105 days between the dates where the sun is in the north at midday (something which makes garden planning quite a challenge!) This period will also mean that on the opposite side of the year, for example, from August 12^th 2025, to April 29^th 2026, will sum to 260 days. Both the dates of August 12^th and the 260-day period are of interest as they reflect very closely the 260-day Chol Q’ij, and the date is a very close approximation to the GMT calculation of the beginning of the fourth era, 11^th August 3114 BCE.

The April zenith transit occurs 40 days after the spring equinox, therefore carrying the same day name within the sacred calendar. In 2025, this will be E’ (Eb) – 4 E’ on the equinox and 5 E’ on the zenith day. The June solstice will fall 53 days later (2 cycles of the sacred calendar and one trecena or 4 trecenas plus 1 day) on the day 6 Kan. The second solar zenith occurs 52 days (4 trecenas) after the June solstice, which will be the day 6 No’j

Zenith tubes have been found at Xochicalco and Monte Alban, indicating that Mesoamerican peoples were certainly aware of the solar zenith.

Experimentation

Part of my philosophy of life is “How can we expect to understand something if we don’t experience it ourselves?” I feel that we must sit under the skies as the ancients once did. So, I decided to make my investigation of the solar zenith by setting up a solar zenith tube in my garden to observe the zenith passage of the Sun myself. These stills are taken from a video I made of my solar zenith observation, which can be seen here https://youtu.be/HxlmSN9rwdo

For the experiment, I used a photographic tripod which has a long centre column with a hole running through it. The centre column is around 300mm in length and the hole is around 5mm in diameter. This is the sort of ratio required to ensure that the direct light of the sun will only be projected when the sun is truly at its zenith. To ensure this, I used a digital level to position the centre column exactly vertical, 90^o on the east-west axis (ecliptic) and 90^o on the north-south axis (meridian).

As the point of zenith approached, a little dot of light began to appear under the tripod. However, at 12:08 pm, I observed a brilliant point of light emerging on the ground, signifying that the Sun was directly overhead. There was a very obvious difference in the quality of light when the Sun was directly at its zenith.

What Does it Mean?

Perhaps one of the questions which could be asked is why the zenith observation would be so important.

Perhaps it could be seen in a way of the energy of the Heart of the Sky entering the Heart of the Earth, bringing fertility? This leads me to the second part of my experiment. Testing the idea of the corn growing season.

For many years, I had heard that the 260 days of the sacred calendar refer to the planting and harvest of corn. I understand from some of my friends here that there are some cultivars which would be planted around the 12^th of February to be harvested around the 29^th of October. These are rather similar to the dates of the solar nadir and also give the dates of the sunrise azimuth of 104^o.

However, many agronomists question this length of corn growth, as it seems far removed from the general length of time from planting to harvest of the corn. Once again, I decided to make my experiment to confirm. In this initial investigation, I used corn from the market. My corn was ripe 80 days after planting. It struck me that the way corn is used in this area is not like that which I would see in my birth country, corn on the cob, but more to be doubled, and dried on the stem. If the solar zenith dates are used as a guideline for planting, they align rather well with the usual weather patterns in highland Guatemala.

The first solar zenith transit date of 29^th April coincides with the onset of the rainy season. Usually, May and June are very warm, wet months, ideal for corn growth. This continues through to around 23^rd July, 85 days after the solar zenith when another astronomical phenomenon occurs. The heliacal rise of Sirius.

Canicular

While I have not directly heard of the observation of Sirius in Maya astronomy, it does indirectly leave its mark in Guatemalan culture as the basis for the Canicular. Canicular is the dry period in the middle of the rainy season. As it is during the hotter part of the year, it is certainly noticeable. If the corn was ripe at 85 days after a zenith planting, this would be an ideal time to double the stems over and allow the corn to dry for 2 weeks before harvest. That would then take us to 99 days after the first solar zenith, giving us 6 days to prepare the field for the second planting of corn before the second zenith. Once again, the Heart of the Sky impregnates the Heart of the Earth on the second Zenith.

Once we pass the second zenith, the rains begin to come back, with September and October being the wettest months of the year. If we are to look at the timing from the perspective of the solar zenith, we would find that 85 days after August 12^th is November 5^th. This is usually the time of year when the rains cease and the dry season begins. It again would be an ideal time to be doubling over the corn ready for harvest 2 weeks later.

As the August zenith is 260 days before the April zenith, whatever day of the sacred calendar the second zenith occurred on would be repeated in the following April. For example, in 2025, August 12^th will fall on 6 No’j (Caban), as will April 29^th 2026.

By following the rhythm of the sacred calendar and the timing of the solar zenith transits, 2 crops of corn can be grown in one season. This maximises the efficiency of the land and enables the people to thrive. It nourishes human hearts through the connection between the Heart of the Sky and the Heart of the Earth.

Here’s the video I made of the observation of the solar zenith transit on April 29th 2025
https://youtu.be/S-012ZJfMjY