# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Astro*Dictionary by Michael Erlewine





1 article for "Placidian Arcs"

Placidian Arcs [Astro*Index]

The first modern system of primary arcs or directions. It was developed by Placidus di Titus, an Italian monk of the 17th Century. It is basically a reworking of Ptolemy's "modes of prorogation", using the then recently discovered methods of spherical trigonometry. It is an accurate mathematical representation of the formula "one degree = one year". He called these equatorial arcs Primary Arcs or Arcs of Direction, a terminology which is still in use.

See also:
♦ Arc of Direction ♦ Directions ♦ Prorogator ♦ Equatorial Arc


Astro*Index Copyright © 1997 Michael Erlewine