Do you think that there is a difference between the arcana Moon and the sephira Yesod, and between the arcana Sun and the sephira Tipharet?
Trumps XVIII and XVIIII are assigned to letters late in the alphabet by modern occultists, who place letters and trumps in order side by side: those who start with alef = LeMat (Fool) put them on qof and reysh respectively, whilst those who start with alef = LeBateleur (Juggler, Magician) put them on tzaddi and qof respectively. Both camps seem happy, so of course neither is right. But there is a numbering system for letters that fits all 22 to trumps that clearly, without stretching, bear out the significance of the shapes and names of the individual letters in the several alphabets prominent since antiquity, namely that given in medieval Irish bardic tradition. It stipulates 0 through 16, while 17-21 (evidently kept secret) are obvious once the rest have been assigned, thus yielding XVIII Moon as qof—Q (Kk),
quert the apple (hence Q's fruit-with-stem shape), glossed in the Book of Ballymote as "shelter of a hind" (hence face taking shelter in moon's orb in Tarot of Marseilles image)—and XVIIII Sun as yod—Y (Ii), Gr.
ischias, the mistletoe or loranthus (Virgil's 'golden bough', whose practice of rooting itself in another tree rather than in earth is why Hebrew yod hovers above the line on which one writes).
Sun and moon have more than one place in the scheme of Kabbalah. But I should first point out that the only error in Hermetic Kabbalah's transmission of the otherwise correct (meaning original or authentic) assignment of the Asiyah world's planetary cycles to Sefirot concerns the sun: they put it at 6, Tiferet, whereas in reality its proper (higher) station is 2, Hokhmah, the great year, which itself more or less
contains 6 and 10 (year and day), being the flux in the relationship between ecliptic (plane of sun's revolution or year) and equator (plane of earth's rotation or day). Indeed 2 (inert helium), 6 (life's carbon), and 10 (inert neon) define the initial structure or 'grid' of the periodic table, but that's another story.
The several sun-moon assignments are:
(1) There are the trumps (XVIIII and XVIII), which correlate them with the appropriate atom-types: potassium, atomic number 19, the mineral which when plentiful in the diet signifies a diet of mostly vegetables, product of the sun's light; and argon, atomic number 18, used to replace air in lightbulbs (so filament won't burn), which are used to imitate the moon.
(2) Then there are the Sefirot in the material or Asiyah world (whose Sefirot are planetary cycles): the sun or great year,
2 (controling or linking
6 and
10); and the moon or month,
9.
(3) Then there is the question of which of the seven 'double letters' (stops B, P, D, T, G, K, and rolled or repeated stop R) correspond to sun and moon. This question is harder than some let on, for the various prominent Kabbalists have assigned them differently (one more symptom an underlying core of knowledge was lost). I have long pondered the question and
still can only offer the
probability that T or tav was the sun and K or kaf the moon. My justification of this would take several paragraphs, but it is reasonably solid. By Irish bardic numbering (what clearly was used by TdM's creators), this means sun's tav is 11—whose digits add to 2, sun's place on the Tree—
tinne the holly, trump XI LaForce signifying what works
through the sun or heart, namely conscience (what controls the lion's jaws); and moon's kaf is 9—moon's place on the Tree—
coll the hazel, trump VIIII L'Hermite signifying what works through the moon or kidneys, namely need to wander off alone (lol, and who's to say tarot's designers had no sense of humor).
There is a
relationship, of course, between planetary cycles and atom-types, for it is apparent that the great year (cycle of precession of equinoxes), being the only cycle measured in tens of thousands of years, points to the time-level of radioactive half-lives, which helium (atomic number 2, first discovered in the light spectrum of the sun) results from, whilst the cycle of 6-carbon IS the year and the cycle of 10-neon IS the day (picture Las Vegas at night).
I am sure all the above has succeeded in doing is showing what a complicated question you asked; for I've only scratched the surface of a proper answer—and even doing that I've undoubtedly said what will cause others here to say, "For shame! what is he talking about?"
May truth light your quest!