Not So Firm-ament

What is the Firmament
This entry is going to look at the subject of the firmament in Genesis 1:6-8, and whether or not the author necessarily understood it to be a solid vault. First the passage in question,

And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.
And 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. And the evening and the morning were the second day. - Genesis 1:6-8

Firmament is an Anglicization of the the Latin word firmamentum found in the 4th century A.D. Vulgate. This word is a translation of the Greek word stereoma found in the 3rd-2nd century B.C. Septuagint, and stereoma is, in turn, a translation of the Hebrew original raqia which derives it's root from the word raqa'. But what does raqia mean? Old Testament scholar Victor P. Hamilton writes in his commentary on Genesis,

The basic meaning of the noun is determined by a consideration of the verb raqa'. Here the basic idea is "to spread out," and specifically the spreading out of the earth at creation (cf. Ps. 136:6; Isa. 42:5; 44:24) or the spreading out of the sky (cf. Job 37:18). In Isa. 40:19 the meaning is to overlay or plate (with gold). A raqia', then, is something that is created by being spread out either by stretching (e.g., a tent) or by hammering (e.g., a metal; cf. Deut. 28:23, in which the sky in a time of drought is likened to bronze; cf. also the use of raqa' in Exod. 39:3, where the meaning is clearly "to hammer out"). - The Book of Genesis: Chapters 1-17, pg. 122

So we see that raqia is a spreading out, but what exactly is it spreading out? Well, many scholars believe that the ancient Hebrews held that the raqia was a hammered out, solid (maybe bronze or crystalline) dome of sorts, that arched over a flat earth. But some scholars aren't convinced that a solid dome is necessarily implied here. For instance, Kenneth Mathews in his commentary on Genesis writes,

God formed an "expanse" to create a boundary, giving structure to the upper and lower waters (1:6-7). The "expanse" is the atmosphere that distinguishes the surface waters of the earth (i.e., "the waters below") from the atmospheric waters or clouds (i.e., "the waters above") . The Hebrew term raqia' ("expanse") may be used for something that is beaten out or spread out like a covering (e.g., Job 37:18; Ezek 1:22-26; 10:1). The stars are depicted as the brightness of the raqia' (Dan 12:3). The atmosphere then is depicted as a canopy or dome spread out over the earth.There is no indication, however, that the author conceived of it as a solid mass, a "firmament" (AV) that supported a body of waters above it. The "expanse" describes both the place in which the luminaries were set (vv. 14-15, 17) and the sky where the birds are observed (v. 20). Thus Genesis' description of the "expanse" is phenomenological--to the observer on earth, the sun and stars appear to sit in the skies while at the same time birds glide through the atmosphere, piercing the skies. In the Old Testament elsewhere there is evidence that the Hebrews understood that clouds produced rain and thus, from a phenomenological perspective, "water" can be described as belonging to the upper atmosphere.

[Note: The English term is derived from the Vg's firmamentum. Job 37:18, which describes skies without rain as a "bronze" expanse (cf. Deut 28:23), is figurative and does not support the common contention that the "expanse" was considered a bronze dome by the Hebrews]. - New American Commentary Volume 1 - Genesis 1-11, by Kenneth Mathews, B&H Publishing Group, pg. 150

In the Genesis-Leviticus: The Expositor's Bible Commentary, Revised Edition, Volume 1 we read,

The sense of the account of the second day of creation is largely determined by one's understanding of the author's perspective or viewpoint. How does the author understand and use the term "expanse" (raqiya`, GK 8385)? Does it reflect a cosmological perspective; that is, is it intended to describe a part of the created universe? For example, Delitzch (96) saw the "expanse" in terms of the outer regions of the universe, "the higher ethereal region, the so-called atmosphere, the sky, is here meant; it is represented as the semi-spherical vault of heaven stretched over the earth and its water." Or does the term describe something in the immediate everyday experience of the author, e.g., the "cloud" that hold the rain? Wenham, 19, appears to take such a view: "Put another way, the firmament occupies the space between the earth's surface and the clouds."  

We must be careful neither to let our own view of the universe or what we suppose to have been the view of the ancients (Gunkel, 107) to control our understanding of the biblical author's description of the "expanse" (raqiya`). Even if we were relatively certain of these viewpoints, we must seek clues from the biblical text itself. One such clue is the purpose the author assigns to the word "expanse" in v.6; it is "to separate water from water." The "expanse" is intended to hold water above the land; that much is certain. A second clue is the name given to the raqiya`. In v.8 it is called "sky" (shämäyim). Finally, we should look at the uses of "expanse" within ch. 1, where the term refers not only to the place where God put the sun, moon, and stars (v.14) but also to that place where the birds fly (v.20: "across the expanse of the sky"). 

Is there a word (in English) or idea that accommodates such a broad use of the term "expanse" Cosmological terms such as "ceiling," "vault," or "global ocean," which are often used for "expanse" in ch. 1, suit neither the use of the term in v.20 nor the naming of the "expanse" as "sky." Such explanations, though drawn from analogies of ancient Near Eastern cosmologies, are too specific for the present context. Thus it is unlikely that the narrative has in view here a "solid partition or vault that separates the earth from the waters above" (Westermann, 116). More likely the narrative has in view something within humankind's everyday experience of the natural world--in general terms, that place where the birds fly and where God placed the lights of heaven (cf. v.14). In English the word "sky" appears to cover this sense well.

The "waters above" the sky is then likely a reference to clouds. This appears to be the view that comes from the reflections on this passage seen in later biblical texts. For example, in the author's account of the flood in ch. 7, reference is made to the "floodgates of the heavens [haSHämayim]," which, when opened, pour forth rain (vv. 11-12; cf. 2Ki 7:2; Pss 104:3; 147:8; 148:4). Deuteronomy 33.26 identifies "the heavens" with "the clouds" (see Ps 36:6; Isa 45:8; Jer 51:9). The writer of Proverbs 8:28 has also understood the term "expanse" and the "waters above it" in Genesis 1 to refer to "clouds" (sh'chäqiym), as does Psalm 78:23. -  Genesis-Leviticus: The Expositor's Bible Commentary, Revised Edition, Volume 1 edited by Tremper Longman III, David E.. Garland written by John H. Sailhamer, Walter C. Kaiser, Jr. & Richard S. Hess, pg. 59

And still others,

1:6 And God said, "Let there be an expanse between the waters to separate water from water." The word translated "expanse" (רָקִיעַ, raqiya`) comes from a Hebrew verb meaning "to stamp or spread, " sometimes of beating out metal into thin sheets. The word is translated as "firmament" in the KJV because of the Latin Vulgate firmamentum implying something firm or solid. But the word only occurs eight times outside of this chapter and always elsewhere in poetic context. Ezekiel 1:22 and Daniel 12:3 describe it as shiny or sparkling. Perhaps this suggest that it was viewed as a glass dome covering the earth. But we must remember that these are poetic texts and the language is undoubtedly figurative. Elihu asks Job, "Can you join him in spreading out the skies hard as a mirror of cast bronze?" (Job 37:18). But again this is poetry and Elihu undoubtedly refers to the mysterious fact that the invisible skies are strong enough to support the clouds (37:16). And furthermore the meaning of a related verb in Hebrew cannot by itself tell us what a noun which is derived from it means. Here the firmament is a hyponym of the word "heaven" or "sky" (שָׁמַיִם shämäyim), that is, it is a synonym for heaven (1:8 God called the expanse "sky"), but refers only to one part of the heavens (1:20 "the expanse of the sky"). The expanse is the space between the water on earth and the water carried in the clouds. In the expanse birds fly and the greater and lesser lights appear. There is no modern English word which is fully equivalent. Our word atmosphere works in part, but we do not refer to the sun and moon as being in the atmosphere (1:14). We must constantly keep in mind that Genesis one is not a scientific treatise, and it uses ordinary language, not scientific language. We also speak of the sun rising in popular language even though we know that scientifically the sun does not rise at all; the earth turns to face it.

1:7 So God made the expanse and separated the water under the expanse from the water above it. And it was so. This time God doesn't merely speak the expanse into existence, he "makes" it and then puts the expanse to work in accomplishing its stated purpose, to separate the waters above and below it. Perhaps this is an instance of the subtle polemic of Genesis 1 against idolatrous cosmogonies that seems everywhere just below the surface. The separation of the waters came only after a colossal struggle in the myths of the ancient Near East. In one of them, Enuma Elish, the firmament is formed by the victorious god Marduk by arching the flayed half of the defeated goddess Tiamat after a titanic struggle. Here God indicates that the expanse should come into existence and then makes it in the most mater-of-fact fashion. There is not the slightest hint of a struggle. 

1:8 God called the expanse "sky." And there was evening, and there was morning-the second day.
The NIV here uses the word "sky" to translate the Hebrew word shämäyim, usually translated "heaven." The connection with 1:1 is thus lost, although the translation is accurate. The expanse is necessary for all nonwater life to have an environment in which to live and is also the necessary preparation for day five when birds, which fly in the expanse, are created. Lacking here is the statement of divine approval, "and God saw that it was good." Perhaps the author viewed the creation of the expanse as merely a preliminary stage to the emergence of the dry land on day three. Another possibility is that, given the fear that ancient people had of the firmament falling, it was important to make it clear that God was in complete control of it. He himself made it and it is, therefore, not to be feared. - Genesis, Volume 1 by Paul J. Kissling, pp 102-104

A Plain Reading
Some argue that a plain reading of the passages in question necessitate a belief in a solid vault in the sky. In support for this argument, they point to the Church Fathers and their traditional understanding of Biblical cosmology. But historians tell us that the Church Fathers were often relying on contemporary Greek cosmology (specifically the Ptolemaic system) to support their understanding of the Bible's cosmology. Often when this is pointed out, the rebuttal is something like, "Well of course they relied on Greek cosmology, because Greek cosmology fits the plain reading!" In what seems a bit of an ironic twist, when someone says something like, "A plain reading of the Genesis narrative doesn't indicate a solid sky to me" I've heard these same people rebut with, "Well that's because you're reading the passage in light of modern science!" So which is it? Does a plain reading of the creation narrative lend itself to a Hellenistic understanding of the universe or a modern one? It seems closer to the truth to say that we often eisegete, that is, read into, scripture the popular knowledge of our present time and place. The Old Testament theologian John Sailhamer writes in his book Genesis Unbound,

The overriding purpose of the most recent interpretations of Genesis 1 has been to reconcile these ancient texts with the discoveries of modern science. In many ways, such a concern has always been an important part of biblical apologetics. Each generation must ask how the Bible fits into its world. Yet if we are to understand Genesis 1 correctly, we must first read it on its own terms--without attempting to reconcile it with current scientific views. The full, rich, theological message of Genesis 1 and 2 must not be lost in an attempt to harmonize them with modern science. When we know what the biblical view is, only then can we attempt to correlate it with science.

History of a Solid Firmament
Let's trace back where the idea of a solid firmament may have come from then. If the majority of Genesis was authored by Moses, we're looking at a writing that was produced in the 14th century B.C. (approx.). If you take a more critical view, Genesis was written in the 6th century B.C. The Jewish Encyclopedia guesses that the idea of a solid firmament and other cosmological traits were derived from the Babylonians. They base this assumption on the writings of 19th century German scholars like Peter Jensen, Hermann Gunkel, and Friedrich Delitzsch, but the idea that the ancient Hebrews heavily borrowed from the Babylonians and other ancient Mediterraneans has been re-examined, and disputed by many modern scholars like Tremper Longman III, Jeffrey Tigay, Nahum Sarna, Shalom M. Paul, Ake W. Sjoberg, Kenneth Kitchen, John Walton, and John Sailhamer who writes, 

Though many have assumed that the Bible shares the world view of the ancient orient, the creation accounts we have from that period are all distinct from the Bible. They are distinctly poetic and manifestly mythological. The biblical account, by contrast, is thoroughly narrative in form and decidedly non-mythological. If we want to understand the relationship between the Bible and the ancient Near Eastern culture in which it was written, we would be wiser to compare the Biblical poetic accounts of creation (as in Job 38) with the early ancient Near East accounts.To compare the narratives of Genesis 1 with the poetic myths of the Babylonians is a classic case of mixing apples and oranges. The primary reason the biblical narratives have been compared with the ancient Near Eastern poetry is that no Near Eastern narrative parallels exist. That, in itself, testifies to the distinctive world view of the biblical creation account. - Genesis Unbound

In his paper, Crucial Questions of Interpretation in Genesis 1, Professor of Old Testament and Biblical Archaeology at Andrews University, Randall Younker, offers an interesting history on the critical view of the firmament,

Firmament in Ancient Mesopotamian Cosmology 

Biblical scholars already in the nineteenth century began entertaining the idea that the ancients believed in a solid vault of heaven. Then, in 1850, Hormuzd Rassam discovered seven tablets in Ashurbanipal‘s library at Nineveh that were found to contain a Mesopotamian creation account, now known as the Enuma Elish. The original composition may date into the late second millennium, ca. 1100 B.C. during the time of Nebuchadnezzar I. One of the first scholars to utilize this creation account in an attempt to reconstruct an ancient Babylonian cosmology was the German Assyriologist Peter Jensen in 1890. In Tablets IV and V the basic Babylonian cosmogony and cosmology were outlined. The creation of the Himmelswölbung ("heavenly vault") appears on line 145 of tablet IV. Works like Jensen‘s added support to the pan-Babylonian school led by scholars like Friedrich Delitzsch (1850–1922), who argued that Hebrews received many of their ideas about primeval history, including their creation story, from the Babylonians during the exile. Soon, a number of critical scholars augmented the Hebrew meaning of raqia' in lexicons, commentaries, etc. by adding the idea of a solid vault, usually composed of metal. 
Then, in 1975, when Assyriologist W. G. Lambert tried to locate the idea that the Babylonians conceived of the firmament as a solid vault in original Babylonian sources, his search came up empty! The closest support he could find was Jensen‘s original 1890 study which translated the Babylonian word for "heaven" in Enuma Elish IV 145 as Himmelswölbung or "vault of heaven." Although Lambert generally admires Jensen's pioneering work, he notes that Jensen made this translation without any support or justification whatsoever. Rather, Jensen simply makes the translation and then proceeds thereafter as if "the point is proved." Apparently Jensen accepted the common assumption that the Babylonians conceived of the firmament in this way and arbitrarily translated the Babylonian word for heaven as a vault! However, after reviewing the evidence, Lambert concluded, "The idea of a vault of heaven [in ancient Babylonian literature] is not based on any piece of evidence." Rather, Lambert notes that the ancient Babylonians viewed the cosmos as a series of flat, superimposed layers of the same size separated by space, held together by ropes; there was no hint of a solid dome.
Lambert‘s study was taken up by his student, Wayne Horowitz, who notes that "although the clear sky seems to us to be shaped like a dome, rather than a flat circle, there is no direct evidence that ancient Mesopotamians thought the visible heavens to be a dome. Akkadian kippatu are always flat, circular objects such as geometric circles or hoops, rather than three dimensional domes." The fact remains that there is no word for a heavenly domed vault in ancient Mesopotamia. 

Translations of Raqia' 

This brings us to the second line of evidence that is used in support of the idea that raqia‘ meant an inverted metal bowl—the translations of the word with the Greek stereōma (LXX/Septuagint) and the Latin Vulgate's firmamentum. Why did the Greek and Latin translators use these words—both of which convey the sense of something solid? According to the Letter of Aristeas, the Septuagint version of the Hebrew Scriptures was commissioned by the Egyptian ruler, Ptolemy (II) Philadelphus, who wanted to include this work in the famous library he was establishing at Alexandria. While all fields of knowledge were pursued in Alexandria, prominent among them was cosmology. The Greeks, who had been aggressively pursuing this topic since the seventh century B.C. in a manner that really must be considered the forerunner of our modern "scientific" approach, were not simply interested in ancient cosmogonies, myths and legends; they really wanted to know the precise physical nature of the universe, including what stuff was made of and how it actually functioned in a mechanical way.
To assist their investigations, the Greeks combed through the astronomical materials of both the ancient Babylonians and Egyptians. Already by the sixth century B.C., Greek discourse on the cosmos had moved beyond the flat disc models common in Egypt and Mesopotamia and were revolving around the idea that one or more solid spheres surrounded the earth (note—these were not half spherical or hemispherical domes or a vault that rested on a flat earth). Thus, ironically, it is from the Greeks that the earliest "metal" sky or sphere model emerges. Interestingly, although we usually associate the debate between a heliocentric cosmology versus a geocentric cosmology to the thoughts of Copernicus and Galileo, the Greeks at Alexandria were already entertaining early forms of these two cosmologies. Therefore, the idea that the earth was enclosed within one or more hard spheres was commonplace within the academy at Alexandria when the Septuagint was being translated and is undoubtedly the main factor (rather than etymology) in the Hellenistic Jewish translators‘ choosing the Greek stereōma for the ancient Hebrew raqia‘. 

Biblical Usage of Raqia‘ 

This leaves us with the final line of evidence for raqia‘—its actual usage in the Hebrew Bible. The basic verb raqa‘ simply means "to stamp, spread out, stretch." The idea is to make something thin by stretching it out. It is important to note that there is nothing inherent in the word that evokes either a specific shape (dome) or material (metal). Raqa‘ is also used as a verb for non-metal objects such as the cloth of a tent or gauze—in which case the idea of "stretching" and "spreading out" makes a lot more sense. Whether the object is hard or soft must be determined from context.
While the uses of raqia‘ in Genesis 1 do not provide any direct indication as to the nature of the material, Gen 1:14, 20 provide some insight from a phenomenological perspective as to how the ancient Hebrews understood raqia‘. In v. 14, raqia‘ is where the sun, moon and stars are located but v. 20 indicates that birds can fly upon it or (better) in it! The full Hebrew expression al-pni raqia‘ is often translated "in the open heavens," meaning "up," "above," or "in" the heavens. In other words, the birds would be flying below the firmament (and the sun, moon and stars) if the raqia‘ was thought of as a solid structure! The text has birds flying in the raqia‘ but clearly at a lower level than the sun, moon and stars. Either the writer conceives of multiple layers or a continuous expanse from the level of the birds to the level of the sun, moon, and stars. Sailhamer, preferring the latter explanation, argues that raqia‘ should be understood simply as "sky." The author‘s own review of Bible commentators from the Byzantine period, Middle Ages, and up to the time of the Enlightenment shows that raqia‘ is commonly translated as "expanse"—something not solid—and not understood as an upside down metal bowl. 

Non-Firm Views of the Firmament Throughout History
I mentioned previously that I often hear the argument that the Church Fathers believed in a solid firmament, and that we should use this to come to the conclusion that the Bible actually teaches a solid firmament, but, while it may be interesting to know what the Church Fathers believed about Biblical cosmology and cosmogony, that doesn't help us determine what the ancient Hebrews, themselves, thought about it. I made the argument above that a plain reading type argument doesn't cut it either, since a plain reading is often tainted by the reader's contemporary cosmological beliefs. But were beliefs about a solid firmament as entrenched throughout history as we're led to believe? Again, though we ought to be wary about using late cosmological beliefs as a litmus test for what the Bible actually teaches (whether for or against a solid firmament) it's interesting to note that historical opinion wasn't quite universal. 

Christian Thinkers 
Christian thinkers seem to have had a number of views about what the firmament was made of and what it actually divided. Some took a very literal view that the firmament was solid and/or literally divided waters from waters (Origen for instance), while others like Augustine (354-430 AD) held a more complicated view that was sometimes a bit literal and sometimes a bit metaphorical,

The waters were divided so that some were above the firmament and others below the firmament. Since we said that matter was called water, I believe that the firmament of heaven separated the corporeal matter of visible things from the incorporeal matter of invisible things. - Two Books on Genesis Against the Manicheans 1.11:17 

It appears that the metaphorical view of the firmament was popular enough among 4th century Christians that Basil the Great (329-379 AD) a contemporary of Augustine wrote a scathing critique of it,

But as far as concerns the separation of the waters I am obliged to contest the opinion of certain writers in the church who, under the shadow of high and sublime conceptions, have launched out into metaphor and have seen in the waters only a figure to denote spiritual and incorporeal powers. In the higher regions, accordingly, above the firmament, dwell the better; in the lower regions, earth and matter are the dwelling place of the malignant. So, say they, God is praised by the waters that are above the heavens, that is to say, by the good powers, the purity of whose soul makes them worthy to sing the praises of God. And the waters that are under the heavens represent the wicked spirits, who from their natural height have fallen into the abyss of evil. Turbulent, seditious, agitated by the tumultuous waves of passion, they have received the name of sea, because of the instability and the inconstancy of their movements. Let us reject these theories as dreams and old women's tales. - Hexaemeron 3.9

From an apologetic standpoint, Augustine, it seems, questioned the material makeup of the firmament, and found a "praiseworthy" theory,

But what is the firmament? Is it that heaven which extends beyond all the realm of air and above the air's farthest heights, where the lights and the stars are set on the forth day? Or is the air itself called the firmament? - The Literal Meaning of Genesis, Volume 1, Book Two, Chapter 1

...a certain commentator has made a praiseworthy attempt to demonstrate that the waters are above the heavens, so as to support the word of Scripture with the visible and tangible phenomena of nature. First of all, he establishes the easiest step in his argument by showing that the air about us is also called "sky" or "heaven." This is true not only in our ordinary speech, in which we refer to "a clear sky" or "a cloudy sky," but also in the usage of Holy Scripture, in which there is mention of the birds of heaven (it is obvious that the birds fly in this air about us); and our Lord, when He spoke of the clouds, said, You know how to read the face of heaven. We often see the clouds gather also in the air near the earth, and in that case settle on the slopes of hills so that most of the mountain peaks tower above them.

The commentator referred to above, having proved that the atmosphere near us is called heaven, wished it also to be designated by the term "firmament," for the simple reason that he divides its space between water in a vaporous state and water in a denser state that flows to earth. The clouds, according to the testimony of those who have walked through them in the mountains, have this vaporous appearance, formed, as they are, of the most minute drops which are gathered and rolled together. And if further condensation takes place, so that one large drop is formed out of many small ones, the air, unable to support it, yields to its weight as it travels, down, and this is the explanation of rain. Hence, from the existence of the air between the vapors that form the clouds above and the seas that stretch out below, our commentator proposed to show that there is a heaven between water and water. This painstaking enquiry is, in my opinion, quite praiseworthy; for the theory advanced is not contrary to the faith, and it makes it possible for one to accept the evidence at hand. - The Literal Meaning of Genesis, Volume 1, Book Two, Chapter 4

A rather novel take is found in the, Philosophia mundi, by William of Conches (1120-1149) who denied that waters could exist above the firmament and insisted that the scriptural passage could only be interpreted allegorically.

Thomas Aquinas (1225-1274) offered a couple of alternating views in his day. The first was that the firmament was the place where the stars were physically located. For this view, Aquinas believed there were three main arguments among philosophers concerning the nature of the firmament. He tells us that, based on Empedocles, some believed the firmament was made up of the four elements; That in keeping with Plato some believed it was made up of only a single element like fire; And that, in keeping with Aristotle, it was made up of a unique fifth element above and beyond the known four. 
The second view that Aquinas mentions appears to be the same shared by Augustine's commentator,

Another possible explanation is to understand by the firmament that was made on the second day, not that in which the stars are set, but the part of the atmosphere where the clouds are collected, and which has received the name firmament from the firmness and density of the air. "For a body is called firm," that is dense and solid, "thereby differing from a mathematical body" as is remarked by Basil (Hom. iii in Hexaem.). If, then, this explanation is adopted none of these opinions will be found repugnant to reason. Augustine, in fact (Gen. ad lit. ii, 4), recommends it thus: "I consider this view of the question worthy of all commendation, as neither contrary to faith nor difficult to be proved and believed." - Summa Theologica, Thomas Aquinas

Aquinas didn't find any of these views particularly compelling, but he didn't find them prohibitive either. The second view in particular wasn't very popular in his day, though a contemporary of Aquinas', Durandus of St Pourçain (c. 1275-1334), put forward a similar view in his Sentences (though it's not known if he actually held the view himself).

The historian Edward Grant tells us in his book, Planets, Stars, and Orbs: The Medieval Cosmos, 1200-1687,  that absolute solidity wasn't something that was much debated in the early Medieval period, 

A widely held opinion today is that scholastic authors thought the celestial orbs were solid, where "solid" is taken as synonymous with hard or rigid. Here the image is one of transparent glass or crystalline globes. Hardly in contention as to popularity with the first opinion today is a second, which assumes that medieval thinkers faithfully adhered to Aristotle's dicta about the celestial ether. Thus the orbs or spheres could be neither solid nor fluid because Aristotle had argued that contrary qualities such as hardness and softness, density and rarity, and so on, were inapplicable to the incorruptible, celestial ether of which they were composted. Nicholas Jardine observes (1982, 175) that to pose a question about the hardness or softness of celestial spheres would have been considered a 'category mistake.' Hardness and softness are qualitative opposites found only in terrestrial matter. Since pairs of opposite qualities are the source of all terrestrial change, they must of necessity be absent from celestial region, where change is impossible. Thus to inquire about the possible hardness or softness of celestial orbs is to ask an irrelevant question. - Planets, Stars, and Orbs, pp. 324-325

What apparently was of considerable importance to Christians (following Augustine) was the nature of the waters above the firmament,

Indeed, the debate hinged on the interpretation placed on the terms "waters" (aquae) and "firmament" (firmamentum), the latter largely determining the meaning of the former... 

From the time of the Church Fathers to the end of the Middle Ages, a variety of interpretations of the waters above the firmament were proposed. The interpreters divide essentially into two groups: those who thought of the waters as solid and hard and those who considered them fluid. Among the former we may include Saint Jerome and Bede...Those who assumed that the waters above the firmament were fluid formed the larger group during the Middle Ages and included Ambrose, John Damascene, Alexander of Hales, Robert Grosseteste, Richard of Middleton, Saint Bonaventure, Vincent of Beauvais, and an anonymous author of a French encyclopedia written around 1400...

Although terms like "crystalline" and "icy solidity" seem to imply hardness, they could be interpreted otherwise...a French encyclopedia...around 1400, declared that 

'Others call it [the ninth sphere] the "crystalline sphere" or the "crystalline heaven" [or sky], not because it is of hard and solid material like crystal, but for its luminosity and its great transparency and uniformity. And it is also the heaven [or sky] that theologians call "watery," not because there are waters such as those which are here below, rather they are light [soubtilles] waters of a noble nature similar to the heaven [or sky] in clarity and luminosity.'

For many, if not most, of those who considered the suprafirmamental waters "crystalline," the latter term did not signify the hardness of the waters but rather their immutability, transparency and luminosity. When medieval authors spoke of the crystalline sphere, they usually had in mind those properties of a crystal such as luminosity, transparency, and even a quasi immutability, rather than hardness. - Planets, Stars, and Orbs, pp. 332-334

Grant goes on to tell us that even up until the late Middle Ages most authors were "vague and noncommittal" about the hardness of the firmament.

The hypothesis of fluid heavens, which went largely unchallenged prior to the thirteenth century, came to have a rival after the introduction and dissemination of Aristolean-Ptolemaic astronomy and cosmology in the thirteenth century. Whereas previously the idea of a fluid or soft heavens was overwhelmingly dominant, the existence of orbs and their possible hardness now emerged as an opposition hypothesis. - Planets, Stars, and Orbs, pp. 338

By the time Tycho Brahe (1546-1601) came on the scene it appears that the idea of a celestial system composed of hard, solid orbs was commonly held by his contemporaries, an opinion that Tycho did not share, and that doesn't seem to have completely fallen out of favor until the 17th century.

Jewish Thinkers
In the 11th century the revered Jewish rabbi Shlomo Yitzhaki (Rashi) seems to have abandoned the Hellenistic idea of a solid raqia altogether in his commentary, and proposed that the heavens were a combination of fire and water,

The word shamayim is a contraction of [a word for] carrying of water, also [a word meaning] there is water, also esh and mim, [meaning] fire and water. He blended them with one another and made the heavens from them. - Rashi's Commentary

Concerning the overall influence of Hellenism on the Talmud and other Jewish commentaries, the Jewish rabbi and philosopher Moses Maimonides (1135-1204 AD) had this to say,

You must, however, not expect that everything our Sages say respecting astronomical matters should agree with observation, for mathematics were not fully developed in those days: and their statements were not based on the authority of the Prophets, but on the knowledge which they either themselves possessed or derived from contemporary men of science. But I will not on that account denounce what they say correctly in accordance with real fact, as untrue or accidentally true. On the contrary, whenever the words of a person can be interpreted in such a manner that they agree with fully established facts, it is the duty of every educated and honest man to do so. - Guide for the Perplexed, Chapter 14

Birds Flying Under or In the Firmament?

And God said, Let the waters bring forth abundantly the moving creature that hath life, and fowl that may fly above the earth in the open firmament of heaven. - Genesis 1:20

One argument I've come across concerning the nature of the firmament is that the Hebrew preposition  al-P'nëy (which literally translates "upon" [`al] "the face" [paniym]) is best translated "in front of" or "before" the raqia. The implication sometimes argued is that birds are flying in front of a solid dome, but cannot fly in it. 
It may be the case that "in front" or "before" is a very good translation for this preposition. We see this in Genesis 1:2 where the same al-P'nëy is used of the Spirit of God moving upon or hovering over the face of the waters, but, as Professor Younker previously pointed out in his paper, this is apparently not the only way the preposition can be translated. Even many modern Bible translations translate the verse something like "across the open expanse" (NIV, ESV) or "in the open firmament" (ASV, ERV). I've been told that this is just apologetic slight of hand done by modern translation teams who can't bring themselves to translate the passage in a more precise fashion because that would tip the hand that the ancient author of the creation narrative did in fact believe in a solid dome. 
One person I discussed this issue with was so adamant (informing me that the plain meaning could simply be verified by looking it up in any Hebrew Lexicon or Strong's concordance), that he'd be very surprised if I could find any scholarly disagreement on the issue, especially among scholars of biblical Hebrew. He hand waved Younker's interpretation as badly mistranslated, and challenged me to find anyone else who would disagree. 
I don't speak ancient Hebrew, but one thing I'm pretty sure about is that speaking and translating another language (especially an ancient one) into English isn't as simple as translating a single word or phrase to determine it intended meaning. Often times scholars only get the sense of a word or phrase through its use in other places and the context of the passage as a whole. So, though al-P'nëy may literally translate "upon" or "before the face", it may not be entirely straightforward to say that that's the only way it can be translated. So, for instance, OT scholars Dr. Claus Westermann, who, though a proponent of a solid dome, and birds flying in front of it, admits,

P describes the living space by using the preposition עַל in two different ways: "Let birds fly above (עַל) the earth, across (עַל) the firmament of the heavens." It is very difficult for us to render the preposition here as it has such a broad scope (emphasis mine); what is intended is, over the earth and under the vault of heaven. Hebrew had to use some such roundabout expression because it had no word for space or atmosphere, where the air was, but only for air in motion (L. Kohler, ZAW 32 [1912] 12). - Genesis 1-11: A Continental Commentary, pg. 137

So, again, although Westermann ultimately believed that what was intended is that birds "fly under the vault of heaven", he makes clear that the issue is far from uncomplicated. Its not as simple as plugging in al-P'nëy and assuming that's all there is to it.

Concerning the supposed apologetic maneuverings of modern Bible translators, it doesn't look like this will fly either. Though Bible translations like the early Wycliffe, and Miles Coverdale use the phrase "vndur the firmament" to describe the flight of birds, the Bishop's Bible of 1568, the Geneva Bible of 1587 and 1599, and the King James of 1611 all translate the passage something like "and let the fowl fly upon the earth in the open firmament of the heaven." This is interesting because contemporary thought on the firmament as a solid, hard dome seems to have been prevalent in the 16th century until (at least) the early 17th century. So these Bibles would have been out of step with the thinking of their day if the assumption was that the birds should have been flying under the firmament and not in it.

Final Words
Over the years I've found that, while discussing this issue with others, oddly enough, those who argue most vehemently against a non-firm firmament aren't unbelievers, but Christians who've rejected a literal reading of the creation narrative for a more metaphorical one. For years I found this very strange (and still do), because, though I hold to a more literal interpretation of the creation narrative, I have no major qualms with those who hold a figurative view. I think there is room for a number of interpretative models on the creation narrative. 

I finally learned from one of these believers that the reason he was so hostile to an open interpretation of Genesis (that allowed even the translation of firmamentum as "expanse"), was because he once went through a period of heavy doubt in his Christian walk attempting to harmonize a literal interpretation of scripture with modern science. He found that by consigning the creation narrative to divinely inspired myth, and taking aim at any view that he felt offered (in his opinion) an edge to a more literal reading, he could resolve that dissonance, and carry on being a Christian. 
This is surely a wrong-headed approach, and seems to me intellectually dishonest. The honest approach is, as Sailhamer pointed out, to figure out what the Biblical view itself is, and go from there.

Up front I'd like to state that, currently, I'm an Old Earth creationist, but unlike many OECs I lean to a more literal interpretation of the creation narrative. I'm currently a fan of John Sailhamer's Historical Creationism theory as presented in his out of print book Genesis Unbound. A thorough and in-depth review of Sailhamer's theory can be found on John Piper's website here, http://www.desiringgod.org/resource-library/articles/science-the-bible-and-the-promised-land.

I also want to mention that I'm not done with this article, and plan on editing and adding to it as I have time. My plan is to add additional citations from historical sources as well as modern scholars.
I'm not a scholar. The above is based on my own informal research on the subject, and I hope and try to keep an open mind. 
I advise those of you who are interested in this subject to study it out yourself, and come to your own conclusions, but to let the spirit of truth lead you as I pray it leads me.