firmament

Firmament is a term used in theology, ancient and medieval cosmology, and literature to denote the sky or heavens. It derives from the Latin firmamentum, meaning a strengthening or support, from firmus “strong.” In early and medieval thought the firmament was conceived as a solid dome or vault that separated the waters above from the waters below and held the stars.

In classical cosmology the firmament often referred to the outer celestial sphere that carried the fixed stars. Some interpretations described the universe as layered or concentric spheres, with the firmament acting as a boundary between Earth and the heavens. In Judeo-Christian traditions the Hebrew raqia is translated as firmament in some Bible translations, notably in older versions, and is associated with the expanse created by God on the second day to divide waters above from waters below.

In modern science the concept of a physical solid firmament is obsolete. Astronomy and physics describe the sky as comprising the atmosphere and outer space, with celestial objects existing in space rather than within a solid shell. Today, firmament survives primarily as a historical or literary term and as a poetic or Biblical reference to the heavens.