Skeptics, just please note the differences between English words pronunciation and spelling between English and American English words. Now see how an American or Westerner pronounces "pure sounds" in Sanskrit, and see how it gets corrupted. Now account for the colloquial affect the unlearned mass brings to the classical words. Now add the flow of thousands of years of world history conquering and conquered nations, migration and conjugation of people and cultures, and the mainstream acceptable history, language and culture being re-written by the mighty latest conqueror.
In architecture, apsis is a synonym for apse.
In Sanskrit, Apas, Apasu, Apas all mean water.
Let see how the "ancients" may have come to this word from their basic building blocks of their classical language, to which the Vedic and the Classical Sanskrit are very closely related, as well as the Ancient Greek.
"Apa" or "Ap" is a prefix which means "down". And "as" and "s" are sounds for verb which connotes verb of "happening". So something that "down happens". Rain comes down, watern flows down, so one can see their is co-relation. But anyway this was a wildest guessing!
Lets see this line here:
From the URL:
A diagram of Keplerian orbital elements. F Periaps, H Apoapsis and the red line between them is the line of apsides. In astronomy, an apsis, plural apsides is the point of greatest or least distance of the elliptical orbit of an astronomical object from its center of attraction, which is generally the center of mass of the system. The point of closest approach is called the periapsis or pericentre and the point of farthest excursion is called the apoapsis (Greek από, from, which becomes απ before a vowel, and αφ before rough breathing), apocentre or apapsis (the latter term, although etymologically more correct, is much less used). A straight line drawn through the periapsis and apoapsis is the line of apsides. This is the major axis of the ellipse, the line through the longest part of the ellipse.
Related terms are used to identify the body being orbited. The most common are perigee and apogee, referring to orbits around the Earth, and perihelion and aphelion, referring to orbits around the Sun (Greek ‘ήλιος hēlios sun). During the Apollo program, the terms pericynthion and apocynthion were used when referring to the moon.
Now first lets look at the usage of the word "apas" in terms describing the space. Remember the Milky way is called "Akash River Ganga". The ancients would draw parallels in the space with the world they would see on the earth. They believes that Microcosm was a reflection of Microcosm. The space was nothing but an "ocean of etheral water" or ether. Anyone who has followed Astronomy would know this.
The plural of "apas" or "apah" is "apaas" or "appah". The instrumental plural is "apseh" or "apses". Somehow the word shows some corruption for plural as "apsides". Here "d" could be corrupted "t" and there is a rule in Sanskrit where "ta" in inserted to make the sound between "s" a bit easier to pronouce. So one can see "apses" becoming "apstes" and then "apsdes". There are some optional rules where the sound "i" is also employed to connect an ending to a constant. So it can also become "apsides". People may be wondering this is a wild guess. Just do the probabilities of alphabets in this patterns keeping the sound close to each other with allowance for changing patterns in accents and enunciations and the way sounds are made by different people from different regions.
Now "ap-apsah" or "apoapsis" means "below/down ethereal water space", and "pra-apsah"/"prati-apsah" would mean "across or opposite ethereal water space", since in Sanskrit "pra" means "going across or forth from a point of reference as prefix" and "prati" means "opposite". For some reasons, the corruption has taken place and "pra" has become "peri", which in Sanskrit means the same as English and Greek "Peri".
Now lets look at the words perigee and apogee. In Sanskrit the root for go is "gam" and week form is "gay" and it can become "gae" (Sanskrit Samprasanna rule or vowel degradation and some vowel combination rule which is one way to look at it but common sense in transliteration of the sounds can also be used here too). Not sure why the "geo"for earth came and it could be also connected. So "apogee" and "perigee" are nothing "apagae" and "pragae" corruptions - in terms for looking for root sounds.
Please see this Sanskrit-iz-ed Words with Simple and Compound Siblants
posting for the word Helios, Sheilesh, or Suresh, which stands for Sun, splendor, epitome of richness and everything (remember Sun was epithet being taken by the Kings and dynasties). So the word "apahelios" and "perihelios" would be "apa-sheelesh" and "pra-sheelesh".
Now moon in Sanskrit is called "Chandram". See what the word was used by NASA - pericynthion and apocynthion. One should know the nasal sounds "n" and "m" are interchangeable in Sanskrit and sound "t" and "d" are related.
People who think this as hocus-pocus, are advised to learn the Sanskrit rules and then see if this sounds correct.
The principle is like a building a chemical formula. It is like seeing Oxide, Nitrate, Nitrite, Sulphate, Sulphide, Phosphate, Hydroxide, etc., bases in different chemical compounds, and see the formulas having something common. Then those knowing Chemistry or Biochemistry would know that the same effect of "commonness" in "prefix", "base" and "suffix" goes on among different compounds which seem unrelated. Just go and check on Amino Acids, Sugar/Glucose/Fructose, Lipids/Fats/Cholesterol/Glycerol/Saccharides etc. All these work base on some formulas and the Ancients understood this principle to come up with their words!