The descriptive panel below, from the Museum of the Bible in Washington DC was posted on Twitter by the historian of Chinese astrology, Jeffrey Kotyk, who posed the question, “I wonder whether Ptolemy would have considered himself “pagan”?”
Reading through the text I have several other comments and queries, but first I will address Jeffrey’s question. Ptolemy lived in the second century CE and was an Alexandrian Greek. At that point in time the Latin word pagan from pāgānus meant “villager, rustic; civilian, non-combatant”. Only in the fourth century did early Christians begin to refer to people who practiced polytheism, or ethic religions other than Judaism as pagans. The word pagan meaning “person of non-Christian or non-Jewish faith” first entered the English language around 1400 CE, so Ptolemy would definitely not have considered himself pagan.
Also referring to Ptolemy, one of the greatest mathematical polymaths of antiquity, as “scholar of the stars” is somewhat limited, not to say strange. The text then attributes a “passion for mathematics, geography, and astronomy” to him but leaves out optics, music theory, and, of course, astrology. Strangely the opening paragraph seems to attribute those things that developed out of astronomy all to Ptolemy alone. What about all the other astronomers, geographers, mathematicians, who existed before Ptolemy, contemporaneously with him, and after him, didn’t they contribute anything?
Of the things listed, “the ability to navigate the earth, determine agricultural seasons, and organise time into days, months, and years,” only the first, navigation, can really be said to have grown out of astronomy. Systematic agriculture and with it, knowledge of the agricultural seasons predates mathematical astronomy by about six thousand years. Days are a natural phenomenon of which homo sapiens would have been aware since they first evolved, although I assume that animals are also aware of days.
The same of course applies to the year of which every sentient creature that lives long enough becomes aware without any help from astronomers. Astronomers, of course, determined how many days there are in a solar year, but they took long enough to get it right.
Months are a completely different problem. If we are referring to lunar months, and after all the word month derives from the word for moon, then the same applies, as to days and years. Although the astronomers had the problem of how to align lunar months with solar years, they don’t fit at all, as became obvious fairly early on and you don’t really want to know about the history of early calendrics. Trust me you don’t, that way lies madness! If, however, we are referring to our current system of twelve irregular months fitted into the solar year, then, although the astronomers played a role, they are largely the result of political decisions.
As a result, the Church was able to use scripture and science to identify and commemorate holy days such as Easter.
Knowing something about the history of the determination of the so-called movable Christian holy days, I cringed when I read this very short paragraph. I will pass over it with the simple comment that these holy days are determined not identified and that determination was a very complex religio-political process stretching over several centuries and astronomers had very little to do with it, other than providing the date of the vernal equinox, which in early days was falsely considered to be the 25 March and providing lunar tables.
I developed the most advanced geocentric model of the universe, at which I believed Earth was the center.
This sentence is, of course, wonderfully tautological, geocentric meaning the earth is at the centre. The sentence is also, as Blake Stacey pointed out on Mastodon after I posted this, “not only redundant, it’s not even grammatical.”
My geocentric model of the universe was accepted until Copernicus, Galileo, and others introduced a heliocentric model.
Ptolemy’s model was extensively modified by a succession of Arabic astronomers and “the most advanced geocentric model of the universe” before Copernicus was that of the Austrian, Renaissance astronomer, Georg von Peuerbach (1423–1461), whose system Copernicus studied as a student.
Galileo, who in reality contributed very little to the heliocentric model or to its acceptance, in fact by rejecting supralunar comets, which orbited the sun, and ignoring Kepler’s laws of planetary motions, he explicitly hindered that acceptance, gets a name check with Copernicus, whereas, Kepler, whose heliocentric model was the one that actually became accepted gets dumped under others!
This is a more than questionable piece of museum signage and I wish I could blame it on the religious nature of the museum but such ill researched signage is unfortunately too common.
The Renaissance Mathematicus 
On the other hand, I’ll bet you that the occurrence of the word “pagan” is due very much to the “religious nature of the museum”. Any other museum would have called him “Ancient Greek”, or perhaps (and better) “Hellenistic”.
Strictly speaking Ptolemy is post Hellenistic. The Hellenistic Period ended in 31 BCE with the Roman conquest of Egypt
It sounds odd to me ear to call him Roman, though I see Wikipedia does. Maybe Alexandrian?
As you can read above I have called him an Alexandrian Greek; Alexandria was very much a multicultural city. He may have been a Roman citizen, I’m not aware of any source for this claim. Alexandria was part of the Roman Empire but being born there didn’t automatically make one a Roman citizen.
The other problem with this bit is that the “paganism” of late antiquity, at least among educated men, was a lot more like Christianity than like the beliefs and practices of the times of Homer or Plato. Ptolemy came earlier than Julian the Apostate or most of the Neoplatonists—I don’t know if he paid any attention to the Christians himself—but his religiosity probably had very little similarity to the cults of the city states or the folk practices of rural folk.