Where does retrograde collide?

In astronomy, retrograde describes motion opposite to the prevailing sense: the apparent east-to-west backtracking of a planet against the stars as Earth overtakes it, or an orbit or spin that runs counter to a system's general rotation. Ptolemy's Almagest already modelled the apparent retrogradation of the planets with epicycles. The referent is a direction of motion defined against a reference rotation, read from position over time. It has nothing to do with a reversed melody or lost memories, which borrow the same word.[1]

Unit

Motion or an orbit directed opposite to a system's prevailing rotation

Recovery means

Not applicable

Measured by

Determined from the body's position, or its angular-momentum direction, tracked over time against a reference frame

In music, retrograde means stating a melody, theme, or twelve-tone row in reverse order, last note first, a device central to canon and to serial composition. Perle's Serial Composition and Atonality describes retrograde among the row transformations used by Schoenberg, Berg, and Webern. The referent is a time-reversal operation applied to a pitch sequence, identified by matching a passage to its backward form. It is distinct from a planet's backward motion or backward-reaching amnesia that share its name.[2]

Unit

A melody or tone row stated in reverse order

Recovery means

Not applicable

Measured by

Identified by matching a passage against the time-reversal of a reference melody or row

In neuropsychology, retrograde amnesia is the loss of memories formed before a brain injury or disease onset, as opposed to anterograde amnesia, which blocks new learning afterward. Such loss is often temporally graded, with recent memories more vulnerable than remote ones; Squire and Alvarez discuss this gradient as evidence for gradual memory consolidation. The referent is a pattern of memory loss defined by its backward reach from an event, read from recall of pre-onset material. It is unrelated to planetary motion or a reversed musical line beyond the common word.[3]

Unit

Loss of memories acquired before the onset of injury or disease

Recovery means

Graded retrograde amnesia may shrink over time as remote memories recover, consistent with ongoing consolidation; dense loss can be permanent

Measured by

Assessed with tests of memory for public events, famous faces, and autobiographical facts from before onset, dated against the injury