What is the firmament called Heaven? First we must define what a firmament is? Firmament means sky, space or heavens. The Bible, in The First Book of Moses called Genesis, God defines what the firmament called Heaven is? "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)
On the second day of creation week, God created a firmament called "Heaven". He created this firmament around the Earth to sustain life that He was about to create in the days of creation. It is the firmament that the birds fly in (Genesis 1:20). It is not outer space, which was created on the first day of creation week. It is the atmosphere that surrounds the Earth. God called this atmosphere "Heaven". God does everything decently and in order (I Corinthians 14:40). God first created outer space (heaven) and the Earth in the beginning. "In the beginning God created the heaven and the earth." (Genesis 1:1)
This firmament called "Heaven" is a unique atmosphere compared to all the other planets in our solar system that have an atmosphere. No other planet in our solar system has an atmosphere that can sustain biological life.
The planet Venus has an atmosphere that is made up of sulfuric acid. The atmosphere is so hot that you would be roasted and dissolved at the same time. Due to the high temperatures and rampant volcanism, the Venusian landscape is a boiling brew of volcanoes, craters, rifts, ridges and chasms. Mars has a very thin atmosphere that is made up mainly of carbon dioxide. If you landed there without a spacesuit, not only would you suffocate but, due to the much lower atmospheric pressure, your blood would boil within minutes.
Earth's atmosphere is so unique that we need to be thankful to God who created it. The oxygen we breathe is only found in our atmosphere. We do not need a space suit here on earth. We truly have "heaven" on earth compared to outer space and the other planets in our solar system.
When the British translators were working on the King James Authorized Version of 1611, they used the Hebrew word "raqiya" (raw-kee'-ah) which means "expanse", "extended surface", or a "thin, stretched-out space. Just look at the pictures from space, and see how thin our atmosphere that surrounds the Earth. It is just a thin, blue line compared to the blackness of space.
Astronomical science has unveiled the mystery of the Earth, and proved that is not the flat throned center of the universe. But is spherical (oblate spheroid ) in form., 7,913 miles in diameter, and racing through space in an endless journey around the sun, and traveling at a speed twenty times faster than a rifle-bullet with the stars always shining but curtained from our daylight sight by our luminous atmosphere.
For more information on Earth's atmosphere go to http://www.wikipedia.org.