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Ecliptic longitude may be expressed in degrees; my understanding is that prior to the 19th century, expressions of ecliptic longitude contained zodiacal signs. What contemporaneous accounts describe the transition away from use of zodiacal signs in expressions of ecliptic longitude and is there a specific occasion that may demarcate the advent of contemporary expressions of ecliptic longitude as standard practice?

Edit: I recognize that the equivalence of mathematical and zodiacal expressions of ecliptic longitude has long been recognized; as use of zodiacal notation fell out of favor in recent centuries, was there an official statement or authoritative discourse that hastened or indicated its demise?

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    $\begingroup$ These two notations are equivalent once the boundaries of the signs are clearly defined. Ptolemy uses both ways to express longitude, and I suppose late Babylonians (Seleucid epoch) also did. $\endgroup$ Aug 28 at 21:54
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Apparently ever since precision in astronomy became really important professionals did use ecliptic coordinates. Hipparchus had demonstrated the precession of the vernal point and its position against the stars as the Zero of ecliptic became problematic. Already Babylonians had two values for it, either as 10 or 8 of Aries; Eudoxus said it was 15 but Hipparchus took it to be 0 (Neugebauer, Sel. Essays p.251) Initially it was thought that the vernal point does not drift through the zodiac but merely oscillates (this was called trepidation). Establishing positions with reference to the vernal point has been preferred as less contenious than the use of constellation limits. Precise values for them were adopted by International Astronomical Union only in 1930.

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  • $\begingroup$ Precise values for constellation limits were adopted in 1930, but establishing position with reference to those limits is not presently preferred. When did preference for using the vernal point supplant using the constellations? How did consensus regarding that preference emerge? $\endgroup$
    – bblohowiak
    Sep 2 at 15:47

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