Firmament

In biblical cosmology, the firmament is the vast solid dome created by God on the second day to divide the primal sea (called tehom) into upper and lower portions so that the dry land could appear.
Bible narrative.
Genesis 1:6–8
Then God said, “Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.” Thus God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament; and it was so. And God called the firmament Heaven. So the evening and the morning were the second day.
Etymology.
The word "firmament" is first recorded in a Middle English narrative based on scripture dated 1250. It later appeared in the King James Bible. The word is anglicised from Latin "firmamentum", used in the Vulgate (4th century). This in turn is derived from the Latin root "firmus", a cognate with "firm". The word is a Latinization of the Greek (), which appears in the Septuagint (c. 200 BCE).
History.
The word "firmament" translates "shamayim" () or "rāqîa" (), a word used in Biblical Hebrew. "shamayim" is translated as "heaven". "Rāqîa" derives from the root "raqqəʿ" (), meaning "to beat or spread out thinly", e.g., the process of making a dish by hammering thin a lump of metal.
The Hebrews believed the sky was a solid dome with the Sun, Moon, planets and stars embedded in it. According to The "Jewish Encyclopedia":
The Hebrews regarded the earth as a plain or a hill figured like a hemisphere, swimming on water. Over this is arched the solid vault of heaven. To this vault are fastened the lights, the stars. So slight is this elevation that birds may rise to it and fly along its expanse.
The 6th-century Egyptian traveller Cosmas Indicopleustes formulated a detailed Christian view of the universe, based on various Biblical texts and on earlier theories by Theophilus of Antioch (2nd century CE) and by Clement of Alexandria ( 150 – 215). Cosmas described a flat rectangular world surrounded by four seas; at the far edges of the seas, four immense vertical walls supported a vaulted roof, the firmament, above which in a further vaulted space lived angels who moved the heavenly bodies and controlled rainfall from a vast cistern. Augustine (354-430) considered that too much learning had been expended on the nature of the firmament. "We may understand this name as given to indicate not it is motionless but that it is solid", he wrote. Saint Basil (330-379) argued for a fluid firmament. According to Saint Thomas Aquinas (1225-1274) the firmament had a "solid nature" and stood above a "region of fire, wherein all vapor must be consumed".
The Copernican Revolution of the 16th century led to reconsideration of these matters. In 1554 John Calvin proposed interpreting the "firmament" as clouds. "He who would learn astronomy and other recondite arts, let him go elsewhere", wrote Calvin. "As it became a theologian, [Moses] had to respect "us" rather than the stars", Calvin wrote. Such a doctrine of accommodation allowed Christians to accept the findings of science without rejecting the authority of scripture.
Scientific development.
The Greeks and Stoics adopted a model of celestial spheres after the discovery of the spherical Earth in the 4th to 3rd centuries BCE. The Medieval Scholastics adopted a cosmology that fused the ideas of the Greek philosophers Aristotle and Ptolemy. This cosmology involved celestial orbs, nested concentrically inside one another, with the earth at the center. The outermost orb contained the stars and the term "firmament" was then transferred to this orb. There were seven inner orbs for the seven wanderers (known planets) of the sky, and their ordering is preserved in the naming of the days of the week.
Even Copernicus's heliocentric model included an outer sphere that held the stars (and by having the earth rotate daily on its axis it allowed the firmament to be completely stationary). Tycho Brahe's studies of the nova of 1572 and the Comet of 1577 were the first major challenges to the idea that orbs existed as solid, incorruptible, material objects.
In 1584, Giordano Bruno proposed a cosmology without a firmament: an infinite universe in which the stars are actually suns with their own planetary systems. By 1630, the concept of solid orbs was no longer dominant.