Prograde

Prograde is an adjective and adverb used in astronomy, planetary science, and geology to describe motion that proceeds in the same sense as a reference direction, typically the rotation of a body or its orbital motion around a primary.

In astronomy and spaceflight, prograde motion most often refers to motion in the same direction as a planet’s rotation or as the planet’s orbital motion around a star. A satellite in a prograde orbit moves around its planet in the same direction as the planet spins (usually eastward). Most natural satellites have prograde orbits, while some are in retrograde orbits, meaning they travel in the opposite direction. Planets orbit the Sun in a prograde (eastward) sense, though individual planets can have other rotational characteristics; for example, Venus rotates retrograde (westward) while Earth rotates prograde.

Prograde motion can also describe the observed, long-term path of celestial bodies relative to distant stars, in contrast to retrograde motion, where apparent backward movement occurs due to observational geometry, such as the Earth’s viewpoint during planetary oppositions.

In geology, prograde metamorphism refers to metamorphic changes that occur during increasing temperature and pressure, typically associated with burial or tectonic heating. This is contrasted with retrograde metamorphism, which occurs during cooling or decompression and the reversal of some mineral reactions.

Etymology indicates prograde comes from Latin pro- “forward” and gradi or gradus “to step/degree,” conveying the sense of forward or advancing motion. The term is commonly paired with retrograde to describe opposite directions.