Back in the days revelation was written they felt the stars were attached to a dome/sky and that keep them from falling down to earth.
http://en.wikipedia.org/wiki/Biblical_cosmology
In the Old Testament the word shamayim represented both the sky/atmosphere, and the dwelling place of God.[30] The raqia or firmament - the visible sky - was a solid inverted bowl over the earth, coloured blue from the heavenly ocean above it.[31] Rain, snow, wind and hail were kept in storehouses outside the raqia, which had "windows" to allow them in - the waters for Noah's flood entered when the "windows of heaven" were opened.[32] Heaven extended down to and was coterminous with (i.e. it touched) the farthest edges of the earth (e.g. Deuteronomy 4:32);[33]humans looking up from earth saw the floor of heaven, which was made of clear blue lapis-lazuli (Exodus 24:9-10), as was God's throne (Ezekiel 1:26).[34]
Grammatically the word shamayim can be either dual (two) or plural (more than two), without ruling out the singular (one).[35] As a result it is not clear whether there were one, two, or more heavens in the Old Testament,[36] but most likely there was only one, and phrases such as "heaven of heavens" were meant to stress the vastness of God's realm.[33]
The Babylonians had a more complex idea of heaven, and during the Babylonian exile (6th century BCE) the influence of Babylonian cosmology led to the idea of a plurality of heavens among Jews.[37] This continued into the New Testament: Revelation apparently has only one heaven, but the Epistle to the Hebrews and the epistles to the Colossians and the Ephesians have more than one, although they don't specify how many.[38]The apostle Paul tells of his visit to the third heaven, the place, according to contemporary thought, where the garden of Paradise is to be found.[39]