What is heaven?
The New King James Version of the Bible uses the word heaven 532 times in 502 different verses. The Hebrew word usually translated "heaven," shamayim, is a plural noun form that literally means "the heights." The Greek word translated "heaven" is ouranos (the same word that inspired the name of the planet Uranus). It refers to that which is raised up or lofty. Both shamayim and ouranos are used variously in Scripture to refer to three different places. (That explains why in 2 Corinthians 12:2 Paul refers to being caught up into "the third heaven.")
There is, first of all, the atmospheric heaven. This is the sky, or the troposphere-the region of breathable atmosphere that blankets the earth. For example, Genesis 7:11-12 says, "The windows of heaven were opened. And the rain was upon the earth forty days and forty nights." There the word "heaven" refers to the blanket of atmosphere around the world, which is where the hydrological cycle occurs. Psalm 147:8 says that God "covers the heavens with clouds." That is the first heaven.
The planetary heaven, the second heaven, is where the stars, the moon, and the planets are. Scripture uses the very same word for heaven to describe this region. For example, Genesis 1 says,
Then God said, "Let there be lights in the firmament of the heavens to divide the day from the night; and let them be for signs and seasons, and for days and years; and let them be for lights in the firmament of the heavens to give light on the earth"; and it was so. Then God made two great lights: the greater light to rule the day, and the lesser light to rule the night. He made the stars also. God set them in the firmament of the heavens to give light on the earth (14-17).
The third heaven, the one Paul speaks of in 2 Corinthians 12, is the heaven where God dwells with His holy angels and those saints who have died. The other two heavens will pass away (2 Pet. 3:10)--this heaven is eternal.