Why is the sky blue? The Old Testament infers the answer 1,000s of years before modern science. Praise the Lord!
Genesis (NRSV)
1:6a "And God said, “Let there be a dome in the midst of the waters,"
1:6b "let it separate the waters from the waters."
1:7 "So God made the dome and separated the waters that were under the dome from the waters that were above the dome. And it was so."
1:14a "And God said, “Let there be lights in the dome of the sky"
7:11d "...and the windows of the heavens were opened."
8:2bc "the windows of the heavens were closed, the rain from the heavens was restrained,"
Psalm 148:4-6 "Praise him, you highest heavens, and you waters above the heavens! Let them praise the name of the LORD, for he commanded and they were created. He established them forever and ever; he fixed their bounds, which cannot be passed."
Proverbs 8:28-29 "when he made firm the skies above, when he established the fountains of the deep, when he assigned to the sea its limit, so that the waters might not transgress his command, when he marked out the foundations of the earth,"
Job 22:12, :14c “Is not God high in the heavens? See the highest stars, how lofty they are!" "...and he walks on the dome of heaven.’"
Job 37:18 "Can you, like him, spread out the skies, hard as a molten mirror?"
Isa. 24:18b "For the windows of heaven are opened, and the foundations of the earth tremble."
"Finally, it is worth pointing out that the world picture of the Jewish people, as reconstructed from various passages in the Bible, was essentially the same as that of the Egyptians and the Babylonians. ...The flat, disc-shaped Earth is surrounded by a sea; beneath the Earth, there are wells and fountains connected with the upper part of the Earth as well as with the great deep, called Tehom. The Earth rests on pillars, and above it is the sky or firmament. Waters are to be found not only on the Earth or beneath it, but also above the firmament."
Helge S. Kragh, Conception of Cosmos, pp. 10
So the sky is blue because a massive molten glass dome holds up an ocean. Also the reason why when looking over the ocean the dark blue does not mix with the light blue all due to an unpassable barrier. Who knew but the Lord.
Even though the Quran mentions terrestrial salt and fresh water seas, there's references though vague are reminiscent of the OT's cosmology (perhaps a vestige of the OT?).
Quran (Pickthal/The Clear Quran)
(PICKT) 21.032 "And we have made the sky a roof withheld (from them). Yet they turn away from its portents."
(TCQ) 21.32 "And We have made the sky a well-protected canopy, still they turn away from its signs."
(PICKT) 25.053 "And He it is Who hath given independence to the two seas (though they meet); one palatable, sweet, and the other saltish, bitter; and hath set a bar and a forbidding ban between them."
(TCQ) 25.53 "And He is the One Who merges the two bodies of water: one fresh and palatable and the other salty and bitter, placing between them a barrier they cannot cross."
(PICKT) 27.061 "Is not He (best) Who made the earth a fixed abode, and placed rivers in the folds thereof, and placed firm hills therein, and hath set a barrier between the two seas? Is there any God beside Allah ? Nay, but most of them know not!"
(TCQ) 27.61 "Or [ask them,] “Who made the earth a place of settlement, caused rivers to flow through it, placed firm mountains upon it, and set a barrier between [fresh and salt] bodies of water? Was it another god besides God?” Absolutely not! But most of them do not know."
(PICKT) 55.019-020 "He hath loosed the two seas. They meet. There is a barrier between them. They encroach not (one upon the other)."
(TCQ) 55.19-.20 "He merges the two bodies of [fresh and salt] water, yet between them is a barrier they never cross."