Calendar Wiki

The All Star Zodiacal Calendar takes inspiration from the Sidereal Calendar.


Rather than months, the calendar is composed of 12 Constellations. They are the signs of the Zodiac:

Year structure - Source: Universe Today
Constellation Order Length Start End
Aries 1 30 21 March 19 April
Taurus 2 31 20 April 20 May
Gemini 3 31 21 May 20 June
Cancer 4 32 21 June 22 July
Leo 5 31 23 July 22 August
Virgo 6 31 23 August 22 September
Libra 7 30 23 September 22 October
Scorpio 8 30 23 October 21 November
Sagittarius 9 30 22 November 21 December
Capricorn 10 29 22 December 19 January
Aquarius 11 30 20 January 18 February
Pisces 12 30-31 19 February 20 March

The Start and End dates are given with reference to the calendar day in year 349 of our era, not long after the Council of Nicaea set the date of 21 March for the Spring Equinox. That is Year 0 of the All Star Zodiacal Calendar. Since the calendar uses the sidereal year, the precession of the equinoxes caused the constellations to shift since the start year.

Zodiacal distance[]

Ptolemy designed the zodiac around year 150. The constellations correspond to 12 zones of thirty degrees along the ecliptic, measured from the position of the Sun at the Spring equinox (northern hemisphere) as set by Ptolemy.

The boundaries of these zones do not fall neatly on the transition between days on Earth.

For this reason, in addition to a year the All Star Zodiacal Calendar indicates the distance between 12 noon on 1 Aries and the entry of the ecliptic into Aries, expressed as an angle. That is the zodiacal distance of the year. Optionally, the zodiacal distance of the constellations can also be provided.

Leap Years[]

The length of the sidereal year is currently 365.2563630 days.

Because the sidereal year is not exactly 365 days, the All Star Zodiacal Calendar features leap days to realign with the stars at regular interval. A leap day is inserted at the end of Pisces every four years on what we call leap years. If we start counting from year 2000, there were six leap days added by year 2024.

Every 78 years an extra leap year is inserted after only two years interval. That is the "short" cycle. After seven short cycles, the next cycle is delayed by four years (one leap year) which makes a "long" cycle of 550 years in total.

Leap cycles
Cycle Repeats row above Length in years 2nd last leap year Last leap year Last interval (years)
Leap year 4
Short x 19 78 76 78 2
Long x 7 550 546 550 4

This scheme gives an average length of the year of:

Illustration of a long leap year cycle:

Bar chart of regular and short intervals in a long cycle