As promised, I shall deal with the passage in Pesachim 94b that describes the sun as travelling behind the rakia at night.
Now, it is of course true that the unidentified “Chachmei Yisroel” of Gemora Pesachim 94b (taken literally) posit that at night, when we do not see the sun, the sun travels “behind the rakia.” And one would reasonably intuit that this indicates they thought the reason we do not see the sun at night is that the rakia (or rather, the back layer of the rakia) is opaque.
But the following question arises: Must we say that this passage shows that Chazal thought of the celestial-rakia as opaque, rendering it at odds with
(a) the Midrash we cited about Avraham Avinu viewing the stars from the back of the rakia, and
(b) the fact likely recognized by Chazal, and certainly by rishonim, that the sun lights the moon?
My answer: Not at all! I will propose, with support from the text, another explanation for how the Gemora Pesachim understands why, at night, when the sun is above the rakia, it cannot be seen.
We note the following:
(a) The Pesachim 94b passage about the path of the sun behind the rakia does not actually say that our inability to see the sun at night is due to any intrinsic opacity or solidity of the celestial rakia
(b) Indeed, no talmudic passage, including this one, actually says that the celestial rakia is either solid or intrinsically opaque.
(c) The expression “עובי הרקיע,” usually translated “thickness of the rakia,” does not in itself inform on the rakia’s texture or transparency. Both the Rambam and the Ralbag also speak of the “עובי” or “עבי” of the spheres, yet they describe the spheres as being ethereal, weightless and colorless. The term “עובי הרקיע” simply refers to the depth—the distance—the rakia spans, whatever texture or substance it may have.
(d) Thus the only feature the Gemora Pesachim 94b does ascribe to the rakia is vast depth.
(e) The preceding Gemara passage describes each of the thousands of the stars we see as specks in the sky to actually be many times the size of earth.
I humbly suggest on this basis that Pesachim 94a is working with the observable fact that distance diminishes the apparent size of objects, to the extent of their ultimate disappearance from sight. This is why those stars, each thousands of times the size of earth, appear to us as mere specks. Now, if the sun travels above the entire vast area of stars, even beyond those stars so far away they can barely be seen, this would account for, and indeed necessitate, that the sun at night must be so far away that it should be impossible to see it at all. We cannot see the sun at night, when it’s behind the rakia, because it is so distant, not because of any opaqueness. The transparent character of the entire celestial rakia, as described by the rishonim, remains intact.
This would fully explain how Chazal could have visualized Avraham seeing the stars from behind the most distant celestial sphere, whereas we cannot see the sun that is behind the dome at night. This would assume there are more stars we cannot see that are further from the earth, as the Gemara implies. (Absence of a filtering atmosphere in space would also contribute to better visibility, but this is not spoken of in the Talmud.)And this would also explain how the sun’s rays, coming from one side of the rakia, could be seen as illuminating the otherwise dark moon, at an angle at which it would be lit in phases by the sun’s rays. (I am speculating that the moon at night does not join the sun behind the dome.
I venture to call this a superior explanation of the passage in Pesachim, because this explanation uses only the very components and features that Gemora passage (together with its contextual surroundings) itself explicitly mentions, without introducing extraneous and speculative factors and components (such as solidity and opaqueness) that, as we have shown, contradict other talmudic and midrashic sources (—although it still remains at odds with the shita that the sun at night travels beneath the earth).
And this would eliminate a machlokess between Chazal, with them all agreeing that the substance within which the stars are located does not have an opaque back.
All the above is following the basic understanding that the Gemora Pesachim 94b is indeed speaking about the daily path of the sun’s body. This is indeed how Rabbeynu Chananel, referencing a “Braissa D’Rabbeynu Shmuel,” takes it. I am also working on another altogether different possibility. ב”נ I will post it in the future if it turns out to be good enough for presentation.
 I say “intrinsically,” because the sky, one of the suggested definitions of rakia, turns opaque colors—blue, gray, orange and red due to the action of the sun’s rays upon it. This, despite the fact that the atmosphere itself is intrinsically transparent. When Chazal say the sky is the color of the sea, it is no more indicative of intrinsic opaqueness than it is indicative of opaqueness when we say the sky is blue.
 Rambam, Moreh Nevuchim 3:14 speaks of עבי הגלגל, and treats it synonymously with the word for “distance”:
(ונם כן היותי שומע תמיד מכל מי שידע דבר מחכמת התבונה, שהוא חושב לגוזמא מה שזכרוהו החכמים ז"ל מן הרחקים, שהם אמרו שעובי כל גלגל מהלך ת"ק שנה , ובין כל גלגל וגלגל מהלך ת״ק שנה)
--and indeed, in Moreh Nevuchim 1:57, he describes the spheres as consisting of non-earthly, indescribable material: “[N]otwithstanding all the efforts of the mind, we can obtain no knowledge of the essence of the heavens—a revolving substance which has been measured by us in spans and cubits, and examined even as regards the proportions of the several spheres to each other and respecting most of their motions—although we know that they must consist of matter and form; but since the matter is unlike sublunary matter, we can only describe the heavens in terms expressing negative properties, but not in terms denoting positive qualities. Thus we say that the heavens are not light, not heavy, not passive and therefore not subject to impressions, and that they do not possess the sensations of taste and smell: or we use similar negative attributes. All this we do, because we do not know their substance.”
Likewise, in Mishneh Torah Hilchos Yesodei HaTorah 3:3 he describes the galgalim as weightless, tasteless, and lacking any aroma, since such properties only exist in the sublunar world.
 Ralbag in his Breishis commentary refers to the rakia’s thickness as a fact in the name of Chazal yet simultaneously describes the rakia as weightless and transparent.
 Also relevant:
מדרש רבה דברים פרשה ב
... (ד"ה ב לג) “ויתפלל אליו [מנשה] ויעתר לו ויחתר לו." מלמד שהיו מלאכי השרת מסתמין את חלונות של רקיע שלא תעלה תפלתו לשמים. מה עשה הקב"ה? חתר את הרקיע מתחת כסא הכבוד וקיבל את תפלתו וישיבהו ירושלים למלכותו ...
Chazal here speak of the “windows” of the rakia, and the “piercing of the heavens,” in an obviously poetical, non-physical way.)
 This speculation must also be made in the approach that the reason the sun cannot be seen at night is that the rakia’s back layer is opaque—which does not solve the problem pointed out, that this would prevent the moon from being lit by the sun.
 The Sefer Hashavas Aveida identifies this braissa with Pirkei D’Rebbi Eliezer.
 Rabbeynu Chananel on Pesachim 94a
ופירש רבינו שמואל בברייתא שלו כי הרקיע עשוי ככובא, הגלגל קבוע והמזלוח חוזרין,
ותניא כדבעינן למימר קמן, כי החמה מהלכת בלילה למעלה מן הרקיע מן המערב למזרח, וכשמגעת לחלון שזורחת ממנו, לאלתר עולה עמוד השחר, והחמה מהלכת בעוביו של רקיע, וכשתגיע לסוף עביו של רקיע לצד הנראה לבני אדם, מיד מנצח על הארץ ומהלכת ביום כולו ממזרח למערב. וכן בשקיעות, מהלכת בעביו של רקיע, וכשתצא מעובי הרקיע כולו--מיד הכוכבים נראין.