In our research of Karahunj Observatory we did not study the problem of Planets observation or calculation. It is necessary to do that in future, because I am sure the Karahunj old astronomers were interested in the Planets. Five planets (Mercury, Venus, Mars, Jupiter, Saturn) were known and had Armenian old names which were presented in Item 1.19.
Old astronomers, of course, saw the unusual (related to stars) movement of planets. The Armenian word for “planet” is ”molorak” which means “errant” or “spinning one”. And indeed, they move sometimes to the back direction. So to understand their real way it was not so easy.
Old astronomers knew about planets the following (even without using any instruments):
1. Planets have different movement than stars, travel crossing constellations, and sometimes stay on one line (”parade” of planets).
2. They are visible from different sides of the Sun, sometimes in the morning before Sunrise and sometimes in the evening, after Sunset, so they perhaps rotate around the Sun.
3. Their velocities on sky are much more than stars velocities, so they sometimes outstrip stars, sometimes move to opposite direction, and they do not blink as stars, so they are much closer to us than stars.
4. Their brightness changes much so they are sometimes at more and sometimes at less distance from us, and their orbit planes are almost parallel to the Ecliptic plane of the Earth.
5. At dark nights in mountains, perhaps, it was possible to see the phases of Venus, Jupiter and understand that planets have not their own light, but are illuminated by the Sun, as the Earth and Moon (the angular size of Venus and Jupiter sometimes comes up to 40″-50″, the normal average resolving power of eye is l’ = 60″, but many people can see twice better).
6. Mercury and Venus are nearer to the Sun than the Earth, because period of their rotation around Sun is less than Earth period, equal to one year or 365.25 days. Period of Mercury is about 2.9 months, of Venus – 7.5 months. Period of Mars is equal to about 1.9 years, of Jupiter is equal to about 11.8 years, of Saturn – 29.5 years, so they are further from the Sun, than the Earth.
7. Periods of planets rotation old astronomers could measure in Karahunj using Stones with Holes directed to their rising (or setting) points on horizon. They could also associate 11-year period of Jupiter rotation with 11-year period of the Sun activity. I think, they knew about the Sun influence on nature, flora, fauna and people on the Earth much more than we know now.
8. The Sun is the Main God, so it is natural that everything around is in His ascendancy and influence, and has to rotate around Him. Karahunj astronomers knowing all these (and supporting it by observations with instruments) could suppose that all planets rotate around the Sun.
Thus the Heliocentric Solar System becomes at first known (as hypothesis) in VI-V millennium BC. It was proved by N.Copernicus in XVI century AD, and then supported by observations of G.Galilei (XVll cent. AD), theories of I.Keppler (XVll century AD) and I.Newton (XVll-XVIII cent. AD).
An extract from the book “Armenians and Ancient Armenia” by Paris Heoruni.