Construct a Solar Astronomical Calendar

by Larry Hecht

The evident success of the ongoing project to measure the retrograde motion of Mars, suggested to me that we are ready to take up another challenge in observational astronomy–the construction of a solar astronomical calendar.

This is a challenge that Lyn posed to us nearly 25 years ago, in part influenced by a trip to India, where he came into contact with the work of turn-of-the-century Indian independence leader Bal Gandaghar Tilak. I first began to seriously take up Lyn’s challenge in connection with my own efforts to understand Tilak’s work some time in the mid-1980s. To be honest, I could not understand at first why Lyn kept talking about “constructing a calendar,” which I thought was something easily obtainable at any stationery store. Once I began to understand what was involved, however, I found that this project led in a number of very interesting directions.

Tilak’s work involves the hypothesis that verses in the sacred Vedic hymns refer to astronomical phenomena, which could only be known by a people living at a point at or above the Arctic Circle. His hypothesis immediately brings into play at least three important and interlocking branches of science: astronomy, Indo-European philology, and climatology, all necessarily subsumed under the topics physical economy and universal history. One of the most provocative aspects of Lyn’s discussion on the subject was the hypothesis that a highly-developed, poetical-musical language, (such as was indicated by the Sanskrit, for example) would be required for the task of recording and preserving astronomical observations over long periods of human history. Rather than the object-fixated grunts of some doomed society of primitive Rave-dancers, forms of verbal action capable of expressing the transformative nature of natural law would be required, including verbal forms capable of expressing the subjunctive mood necessary for any hypothesis, varying degrees of completion of action, and many other subtleties.

Attempting to read Tilak’s {Arctic Home in the Vedas,} however, produced some immediate problems. Early in the book, the author began talking about astronomical phenomenon, such as the precession of the equinox, the seasonal motions of the Sun, and the relationship of the Sun to the zodiacal constellations, which, I soon realized, I had no real understanding of. To make any sense out of his thesis, it was clearly necessary to have some grasp of these things, so I decided at some point to dig in and make the effort. As I had been reading books about astronomy since childhood, it was something of an embarassment to have to admit to myself that I could not even explain the meaning of the seasons in any cogent way. A joke which Jonathan T. had been making at that time had stuck in my mind, and was helpful in overcoming the embarassment. The joke, which I think he may have included in the title of a Fusion magazine article he wrote at the time, was the phrase “Astronomy without a Telescope.”

A Simple Calendar Observatory

The method I suggest here for constructing a solar astronomical calendar, is not an exact replica of the steps I took. However, I think it will work, and, under the present circumstances, where collective and enthusiastic pedagogical activity is taking place all around, it should allow us to proceed quickly and happily.

I suggest we begin by constructing something which will resemble, in principle, the famous Stonehenge, an historical artifact which has unfortunately taken on all sorts of cult-like significance, but which is actually just one of many still-standing astronomical observatories from the Megalithic period. Our observatory will be much simpler. Probably the most difficult part of this project will be to find a level site with a good view of the horizon, especially to the east and west, to which we can return regularly. The calendar observatory need consist of no more than some stakes in the ground, arranged around part of the circumference of a circle, and one stake at the center.

Now, here is what I suggest we do. On the first day, we make two observations, one at sunrise and one at sunset. We begin by locating a center for our circle, and driving a stake in the ground at that point. This will be the siting post for all the observations. Now, choosing an appropriate circumference for our circle, and using a rope or chain to keep a constant distance, we plant a stake in a line from the siting post to the point where the Sun rises over the horizon. We return before sunset, and similarly drive a stake in the ground on the other side of the circle where we see the sun set.

That simple observation, repeated over the course of a year, will provide us with an experimental understanding of many important concepts in astronomy, including the summer and winter solstice, the vernal and autumnal equinox, and the equation of time (which, by the way, bears a certain relationship to the lemniscate). But this is only a beginning. For, using no more than our simple observatory, we may next begin to observe the motion of the Sun, not only with respect to fixed positions on the ground, but also with respect to the stars. From this we may develop many new concepts, including that of the precession of the equinox, which plays an interesting part in this history of science, which, we shall also come to see, is the history of language.

But we will also have an advantage over our predecessors, who were carrying out such observations probably tens of thousands of years ago, several cycles of glaciation back into the pre-historic past. By use of modern means of communication, we will be able to rapidly compare observations made at widely divergent positions on the Earth. We shall have the great advantage of having access to observations at the high northern latitudes of Stockholm and Copenhagen, the near-equatorial latitudes of Bogota and Lima, and many middle latitude sites in both the Northern and Southern Hemispheres. This will really make for some fun, some paradoxes, and definitely ensure that there is no “right answer” to be looked up in the back of the back.

To start out, I suggest we take the time to explore and secure a good site for our calendar observatory, and begin with the first very simple observation of marking the rising and setting points of the Sun. Between these points, we will have a circular arc on the ground, whose angle can be measured and recorded. It would also be useful to make some observations of the path of the Sun in the sky over the course of a day. From this observation and the position of our two stakes in the ground, we should also be able to come to a clear understanding of the meaning of North, South, East and West, and also of the word Noon. For some added fun, we might try to measure the highest declination of the Sun, and observe what time it occurs on our watches.

With the measure of the circular arc between the two stakes in the ground recorded, it will be most interesting to immediately compare the results with those found on approximately the same day at other calendar observatories around the globe, as one could do, for example, on an international youth call. If it should happen that some of the observations should take place around the 22nd of September, a very interesting paradox will arise when the observations from different latitudes are compared. (The path of the Sun and its position at Noon ought also to be observed on that day.) But it will only get more interesting, as the subsequent observations are taken, and compared for the different latitudes.

So, let the fun begin.