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AH020387
22-02-2012, 15:16
Why is is said. "look east at dawn on the spring equinox to see the zodiacal constellations"?! why on the spring equinox?! why cant i view the constellations on ANY normal day?!

Minderwiz
23-02-2012, 05:06
Why is is said. "look east at dawn on the spring equinox to see the zodiacal constellations"?! why on the spring equinox?! why cant i view the constellations on ANY normal day?!

Well that's not a saying I've particularly heard but the only immediate answe I can think of is that at the equinox the Ascendant (the point where the horizon intersects with the ecliptic) is due East at sunrise. This is true for both equinoxes but is not true of any other day of the year, as the Ascendant varies over the year between somewhat North of East and somewhat South of East (the amount of displacement from due East depends on laititude)

In the Northern Hemispehere the Ascendant, at sunrise, moves gradually North of East from Spring Equinox, reaching its most northerly point at the Summer Solsitice, it then moves southwards till at the Autumnal Equinox it is again due East. It then moves South of East reaching it's maximum southerly point at the Winter Solstice (For the Southern Hemisphere simply reverse the seasons).

Incidently on a daily basis, each time that 0 degrees Aries and 0 degrees Libra rise, they are due East - that is the annual cycle of the Sun's rise is repeated on a daily basis with the ascending degrees of the ecliptic.

Now, strictly speaking my answer applies to the ecliptic, the Sun's observed path,. The Zodiac is a band of around 9-9 degrees either side of the ecliptic. The Sun can never be off the ecliptic, so it will always rise due East at the equinoxes, but all the other planets can and do have latitude north or south of the ecliptic, so even on the day of the equinox all of them are likely to rise either a bit North or a bit South of due East

The overwhelming majority of Astrologers, including Vedic, Traditional and Modern, Astrologers, do not use Constellations. For them, the Zodiac circle is divided into twelve equal segments, measured from an arbitrary point (usually the Spring Equinox or a calculated point which keeps the spring equinox in the constellation of Aries (but the other signs don't match up to the constellations with any exactness). This means that even the actual constellations of Aries and Libra are not due East at the time of the Spring and Autumnal equinoxes respectively.

Barleywine
24-02-2012, 22:55
Interesting that this topic should pop up now, just when I finished writing detailed study material on "the astronomy of astrology" for a class we will be giving this summer. I wonder how many people realize it's the rational horizon (aka sensible or celestial horizon when projected onto the celestial sphere) that intersects with the ecliptic to form the Ascendant. This is the plane parallel to the visible horizon that passes through the center of the Earth, making it a "great circle." As Minderwiz says, the Ascendant is due east along the rational horizon at the Vernal Equinox , but might appear slightly off from that point on the visible horizon due to the latitude of the observer. There are good drawings of the components of the "celestial sphere" in many books, but they don't all do a good job of making clear the position of the observer at the center of it all, and how local latitude affects the visible location of the rising and setting points (but not the noon or midnight points, which are pegged to the celestial meridian and not the rational horizon).

I had some excellent source material in Jeff Mayo's "Astrology" and the "Larousse Encyclopedia of Astrology." I don't have de Vore, but that must be similarly good. And I'm sure there are many others (perhaps Alan Oken?). Unfortunately, I'm not a full member so I can't post any of my material. I'm thinking of trying to publish if there is any perceived need for a refresher in this area. As a former engineer, I especially enjoyed figuring out the mechanics of right ascension (and its uses), retrogradation and precession of the equinoxes (I used to think it was a the relative velocity of the Milky Way - and the solar system - to the fixed stars, magnified by their vast interstellar separation, that caused that. Oops . . . :)).