(Continuation of the post "Path of the zenith of the sun")
At the deepest night of June 21st at the Tropic of Cancer in the Sahara directly above me at 90° in the zenith, however, I do not exactly see the of border of the star constellations of Capricorn and Sagittarius, but only the rear end of the rising Sagittarius (Sagittarius rises backwards up and through the sky).
And yet, since the zodiacal boundary between Capricorn and Sagittarius is directly 180° opposite of the zodiacal boundary between Gemini and Cancer, where I had been the sun in the zenith exactly above me just twelve hours ago (on this 21st June; if only I could have seen the stars behind the sun during the day ...), actually I should be looking exactly at the boundary between Sagittarius and Capricorn according to my reasoning. But I am not.
After all, many places in the Tropic of Cancer have signs with inscriptions such as "Tropic of Cancer" (Oman) or "Tropico de Cancer" (Mexico); sometimes even monuments were erected to mark the Tropic of Cancer, for example in the district of Hualien in Taiwan. Likewise, the author Henry Miller titled his (surrealistic and burlesque) novel published in 1934 with "Tropic of Cancer"; his successor novel from 1939, he consequently titled his "Tropic of Capricorn". In fact, such "Tropic of Capricorn" waymarks and signs also exist at the southern Tropic of Capricorn: in Atsimo-Andrefana in southwest Madagascar, for example, a stone board with a reddish capricorn painted on it says "vous franchissez le tropic de capricorn" (you are crossing the Tropic of Capricorn); near Itai at the Tropic of Capricorn in Brazil there is a sign similarly saying "aqui passa o trópico de capricórnio" and at the Tropic of Capricorn on the Stuart Highway in Australia, a globe-shaped monument has been erected. Last but not least, for centuries folklore and literature have only spoken of the Tropic of Cancer and the Tropic of Capricorn when trying to locate and name the latitude of the summer or winter solstice.
With all these examples from social life, I am really surprised (on this deepest night of June 21st) to only see the rear end of the Sagittarius at the zenith of the starry Sahara sky above me. May it be that the fixed starry sky above me is not as fixed as I was assuming? Which misconception have I fallen victim to here, or how can I explain this deviation that is immediately visible to me? Which misconception did I fall into here, how can I explain this immediately visible discrepancy?
This is how it must have been: at the time the tropics were named, the zenith of the sun was almost exactly in front of the starry background of the constellation borders between Gemini and Cancer or Sagittarius and Capricorn, respectively, on the day of the summer or winter solstice, which can be dated astronomically to the year 10 BC. For the late Greeks and the Romans, but also in the first centuries after Christ, the solstices must have appeared relatively exactly or near the constellation boundaries of Gemini-Cancer and Sagittarius-Capricorn - hence the name.
Since then (or even before that, i.e. continuously) the fixed starry sky at the time of the summer and winter solstice (and also at the vernal/autumnal equinoxes and in general) has been slowly receding by about 1° every 72 years. This means, for example, that the summer solstice from about 1450 B.C. to 10 B.C. had taken place in front of the starry background of the constellation of Cancer (and the winter solstice correspondingly in front of the starry background of the constellation Capricorn). As of 10 B.C. until 1989 A.D. the sun had turned its course at the summer solsitce in front of the starry background of the constellation of Gemini. From 1990 to 4610 AD (i.e. as of our current day and age), the sun is being located in front of the starry constellation of Taurus at the time of the summer solstice.
Correspondingly, the other constellations of the ecliptic - because they are connected to each other like a band - have moved backwards by about 1° every 72 years, i.e. at the same time of each solar year (i.e. if the earth has reached the same position on its elliptical orbit around the Sun every year), the band of constellations has (apparently) also moved backwards minimally: it is no longer at exactly the same position as in the prior year. Therefore, over the centuries and millennia, this shift has occured, this shift which today in 2020 I can perceive right here in the nocturnal Sahara in Murzuk at the Libyan-Chad-Nigerian "border" (15° eastern longitude, 23.4° northern latitude). But has the band of constellations really shifted backwards in the course of time or is this - as many things in the desert may be - just an appearance behind which there lies another explanation?
(Continuation in the posts "Cycles of Precession/ Yugas"
or "The story of Larry Reavis")