Retrieving "Prograde Direction" from the archives

Cross-reference notes under review

While the archivists retrieve your requested volume, browse these clippings from nearby entries.

1. Ecliptic Longitude

   Linked via "prograde direction"

   The ecliptic coordinate system is fundamentally heliocentric, though it is commonly applied to geocentric observations. Longitude is measured in angular units, typically degrees ($^\circ$), arcminutes ($'$), and arcseconds ($''$). A complete circle is $360^\circ$, corresponding to a full circuit around the sky following the Sun's apparent trajectory.
   The zero point, or origin, for ecliptic longitude is the Vernal Equinox ($\Upsilon$), which, by definition in modern [astronomy](/entrie…