Sidereal Zodiac Signs

ZODIAC, an ecliptic coordinate system.

“It was only for mathematical reasons that a definite great circle which measured the progress of the sun and the planets with respect to exactly 30°-long sections [of ecliptic longitude] was introduced. Indeed, the zodiac was hardly ever more than a mathematical idealization needed and used exclusively for computing purposes.”

—Neugebauer, The Exact Sciences in Antiquity

Aries

April 14–May 15

[0° Aries = Aldebaran − 45°] The Sun enters Aries on either the 14th or the 15th of April, depending on the time zone and whether or not a leap year is in effect.

Taurus

May 15–June 15

[0° Taurus = Aldebaran − 15°] The Sun enters Taurus on either the 15th or the 16th of May, depending on the time zone and whether or not a leap year is in effect.

Gemini

June 15–July 17

[0° Gemini = Aldebaran + 15°] The Sun enters Gemini on either the 15th or the 16th of June, depending on the time zone and whether or not a leap year is in effect.

Cancer

July 17–August 17

[0° Cancer = Aldebaran + 45°] The Sun enters Cancer on either the 17th or the 18th of July, depending on the time zone and whether or not a leap year is in effect.

Leo

August 17–September 17

[0° Leo = Aldebaran + 75°] The Sun enters Leo on either the 17th or the 18th of August, depending on the time zone and whether or not a leap year is in effect.

Virgo

September 17–October 17

[0° Virgo = Aldebaran + 105°] The Sun enters Virgo on either the 17th or the 18th of September, depending on the time zone and whether or not a leap year is in effect.

Libra

October 17–November 16

[0° Libra = Aldebaran + 135°] The Sun enters Libra on either the 17th or the 18th of October, depending on the time zone and whether or not a leap year is in effect.

Scorpio

November 16–December 16

[0° Scorpio = Aldebaran + 165°] The Sun enters Scorpio on either the 16th or the 17th of November, depending on the time zone and whether or not a leap year is in effect.

Sagittarius

December 16–January 14

[0° Sagittarius = Aldebaran + 195°] The Sun enters Sagittarius on either the 16th or the 17th of December, depending on the time zone and whether or not a leap year is in effect.

Capricorn

January 14–February 13

[0° Capricorn = Aldebaran + 225°] The Sun enters Capricorn on either the 14th or the 15th of January, depending on the time zone and whether or not a leap year is in effect.

Aquarius

February 13–March 15

[0° Aquarius = Aldebaran + 255°] The Sun enters Aquarius on either the 13th or the 14th of February, depending on the time zone and whether or not a leap year is in effect.

Pisces

March 15–April 14

[0° Pisces = Aldebaran + 285°] The Sun enters Pisces on either the 15th or the 16th of March, depending on the time zone and whether or not a leap year is in effect.

NOTE: Due to precession, these calendar dates will move forward by one day approximately every 72 years.

The ancient Babylonians formulated the base 60 sidereal zodiac in the mid-5th century BCE; and just six hundred years later, with his Tetrabiblos (c. 150), Ptolemy untethered it from the stars and bound it to the equinoctial and solstitial points. This was made possible as a result of the fact that during Ptolemy’s time the vernal point was fast-approaching a perfect 45°-alignment with the fixed star Aldebaran.

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