What is Sidereal Astrology?
Ancient astrology was based on an observed connection between the presence of certain bright "marker stars," such as Sirius and Regulus, in the night sky and the personalities of people who were born at that time of year. These “marker stars” became associated with the constellations which they were located within. Since the apparent motion between stars is extremely slow (1 degree every 120,000 years), these constellations provide a relatively fixed frame of reference against which to measure the movement of planets (the “wanderers”). Sidereal, by the way, literally means “star” or “constellation,” so sidereal astrology is astrology that is based on marker stars.
Many people don’t realize that the dates for each zodiacal sign commonly used in tropical, or “western” astrology no longer correspond to when those constellations are visible in the sky! For example, we define a “Virgo” as being someone born between 8/23 and 9/22. However, the truth is tat the constellation Virgo will not be overhead until around 9/17! How did these dates get so far out of sync with the constellations?
In the third century, the constellation Aries happened to be roughly aligned with the spring equinox. Scholars today debate the process by which the equinox subsequently became confused with the start of Aries. Some feel that the equinox was simply easier to measure for the common man; others claim that the Greeks misinterpreted ancient Egyptian and Babylonian records. Either way, over time western people began to automatically measure 0 degrees Aries from the spring equinox, and count off the subsequent signs from there.
So, what’s the problem? Well, the equinox is not in fact “fixed” in the same way the stars are. In fact, the equinoxes “process” (or move backward) through the ecliptic plane of constellations by one degree every 71.5 years. This is why we correct our calendar by adding one day to the year every 4th “leap” year, so that the equinox and our seasons don’t get out of sync. However, since there has been no similar correction made to the tropical zodiacal attributions, over hundreds of years the “0 degrees Aries” of western astrology has moved up by 24 degrees, into the period when Pisces is actually still overhead. I say that this is true in “western” astrology because easterners never adopted the false equinox demarcation. This is why sidereal astrology is sometimes called “Hindu astrology,” after the major system of the east.
Even with the sidereal astrology, there are different measuring systems, although the effective differences between these systems are quite small. For example, Cyril Fagan, who revived sidereal astrology in modern times, chose to use Spica (in Virgo) as his key measuring point, while MacGregor Mathers used Regulus (in Leo) for all Golden Dawn work. Since the relative distance between these stars changes so incredibly slowly over time the marker star chosen is of little consequence in terms of measuring sidereal time.
To convert to sidereal astrology for use in magic (as recommended by Mathers), you can either subtract 24 degrees from the measure shown on a tropical astrology calendar, bearing in mind that you will probably drop back a sign, or else you can add six degrees to tropical longitudes and just subtract a sign. Or you can use the chart below to show the approximate current starting date for each sign
Note that Pisces is listed first since the spring equinox
now occurs therein (at about 5-1/3 degrees Pisces). Hence, at this time
we are still in the Age of Pisces as determined by the occurrence of the
spring equinox in the constellation Pisces.