What is the definition of firmament?

Answer 1

The vault of the sky.

To the ancients, the firmament was a solid dome that held up the primeval waters, while the sun and moon were in the sky below the firmament. Stars were thought to be holes in the firmament, allowing the light of the heavens to shine through.

Amongst Talmudic scholars the firmament is generally accepted to mean outer space or the earth's atmosphere. The Talmud actually teaches that there are seven firmaments, the one we see (the sky) being the first. It is also taught that the firmament is made up of fire and water, basically describing the Earth's atmosphere.

The firmament was a layer of water vapor that at one time covered the entire earth. We see the remnants of that layer today in the form of clouds.

Answer The Jewish Encyclopedia describes the Firmament as follows: "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 book of Genesis goes on to mention lights being placed in the firmament (Genesis 1:14-17):

And God said, "Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years: And let them be for lights in the firmament of the heaven to give light upon the earth": and it was so. And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: the stars also.

According to traditional commentary, the word Rakia (firmament), like certain other words, may indicate more than one thing. In Genesis 1:20 concerning the birds, it refers to the vault of the sky, against which we see the birds fly. In 1:14 concerning the sun, moon and stars, it refers to what we call outer space. And in the Talmud, Hagigah ch.2 concerning the upper worlds, it refers to the limit between each two of the upper worlds.

Answer 2

Genesis 1:6 says that God created the firmament on the second day. To the ancients, the firmament was a solid dome that held up the primeval waters, while the sun, moon and stars were in the sky below the firmament. They thought that the sky literally touched the earth at the horizon and was a solid part of the universe just as much as the earth itself. Interestingly, if we do not believe that the firmament is a physical reality, then nothing was created on the second day.