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Prograde or direct motion is more normal motion in the same direction as the primary rotates. However, "retrograde" and "prograde" can also refer to an object other than the primary if so described. The direction of rotation is determined by an inertial frame of reference, such as distant fixed stars.
Retrograde (backward) and prograde (forward) are observed as though the stars revolve around the Earth. Ancient Greek astronomer Ptolemy in 150 AD believed that the Earth was the center of the Solar System and therefore used the terms retrograde and prograde to describe the movement of the planets in relation to the stars. Although it is known ...
A satellite with an orbital inclination between zero and ninety degrees is said to be in what is called a direct or prograde orbit, meaning that it orbits in the same direction as the planet's rotation. A satellite with an orbital inclination between 90° and 180° (or, equivalently, between 0° and −90°) is said to be in a retrograde orbit.
Prograde can refer to: Retrograde and prograde motion, in astronomy, a type of motion of astronomical bodies; Metamorphism#Prograde and retrograde, in geology, describes mineral changes in rocks under increasing pressure and/or temperature conditions; Progradation, in geography / geomorphology, refers to the growth of a river delta
Metamorphism is further divided into prograde and retrograde metamorphism. Prograde metamorphism involves the change of mineral assemblages (paragenesis) with increasing temperature and (usually) pressure conditions. These are solid state dehydration reactions, and involve the loss of volatiles such as water or carbon dioxide.
Five planets are going to be retrograde in the summer of 2024. Here are the dates for Mercury retrograde, Venus retrograde, Saturn retrograde, Neptune retrograde, Pluto retrograde and more.
No, Mercury isn't the only planet that goes retrograde.
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