Explaining the Calendar

There is one more factor I’d like to explain in a bit more detail as well: the calendar.

Four Type of Calendars

Although it might be obvious to some of you, I still like to start with what a Calendar actually is. This is what I found on the internet:

“A calendar is a tool that measures, divides, and organizes the continuous flow of time into recurring, structured periods. The smallest unit it measures is the ‘day,’ while the largest is the ‘year’ — both of which are defined by the calendar itself. The primary purpose of any calendar is to identify points in time, track durations, and organize the passage of time into distinct yet cyclical intervals. Calendars, whether ancient or modern, are ultimately rooted in astronomy. They develop from observing and recording the constant motions and interactions of the Earth, Sun, Moon, and stars.”

All ancient calendars originated from careful observations of the Sun, Moon, and stars, transforming these celestial patterns into numerical measurements. Through this process, early astronomers identified three natural units of time:

• The solar day – from sunrise to sunrise (or sunset to sunset).
• The lunar month – from new moon to new moon (or full moon to full moon).
• The tropical (solar) year – from summer solstice to summer solstice (or March equinox to March equinox).

It’s important to note that calendars can therefore only be designed for one of four distinct purposes, which cannot be combined. You have to choose.

1. Fix the Sun’s Position as seen from Earth on a Specific Date

   This is known as a (Solar calendar ).

   So March Equinox (the day length of 12 hours day, 12 hours night)) or Summer Solstice (Sun highest in the sky) fixed on a date.

   As a result the background stars will move across time and the moon phases are not in line with the months.

2. Keep the moon cycle as observed on Earth fixed on a specific cycle

   This is known as a Lunar calendar .

   A lunar calendar follows the phases of the Moon (e.g. from new moon to new moon). If you follow such calendar, the solstices and therefore the experienced seasons will move across time. Additionally the background stars will move across time as well.

3. Combine Lunar and Solar Alignments

   This is known as a (Lunisolar calendar )

   A lunisolar calendar primarily follows the lunar cycle but occasionally adds an extra month to realign the months with the seasons. This adjustment keeps the calendar somewhat aligned with the solar year, but over time, the background stars continue to drift.

   One major drawback is that the length of the year fluctuates, making some years longer than others which complicates long-term planning.

4. Fix the Position of the Stars on a Specific Date

   This is referred to as a stellar or star calendar.

   In this type of calendar, a specific date (such as March 21) is linked to a constellation—for example, Pisces.

   Although I haven’t found historical references to such a “sidereal year” calendar, it’s theoretically possible. If you follow such calendar, the solstices and therefore the experienced seasons will move across time AND the moon cycles also do not play any role. Additionally because the length of year is based upon a MEAN Sidereal day, there could be some small fluctuations. That could all be even more confusing.

Western civilization chose to create a calendar that keeps the March equinox fixed on March 21. The calendar we use today — the “Gregorian calendar” — is therefore classified as a “solar calendar”. This design inevitably causes the background stars to shift over time.

The J2000 values for the length of a solar year are: 

• March Equinox 365.242 374 04 + 0.000 000 103 38 x a days
• June Solstice 365.241 626 03 + 0.000 000 006 50 x a days
• September Equinox 365.242 017 67 - 0.000 000 231 50 x a days
• December Solstice 365.242 740 49 - 0.000 000 124 46 x a days (9)

The average from the above periods is currently ~365.2421896 days (of 86,400 ephemeris seconds a day) according to this website.

As observed, the lengths of the seasons are not equal, causing the duration of the solar year measured at the March equinox to be slightly longer than the average solar year. This occurs because Earth’s position in its orbit during solstices and equinoxes shifts gradually each year. A process that takes 18,636 years to complete one full cycle.

On the March equinox, this effect creates a difference of 7 minutes, resulting in a right ascension (RA) of 23h53m at 12:00 UTC on March 21, instead of the expected 0h.

Solar Calendar attempts

Now that we have a better understanding of the solar calendar’s purpose, let’s examine the three major attempts to design solar calendars aimed at keeping the March equinox fixed on a specific date (March 21 at 12:00 UTC).

While many earlier calendars were developed, most are poorly documented and open to interpretation. To stay focused, I will only cover the three most significant solar calendar systems.

1. The Julian calendar 

   The Julian calendar was introduced in 46 BC to honour Julius Caesar, who brought stability to the Roman Empire.

   The calendar began with an initial extended year of 445 days (known as the annus confusionis) to realign the equinox on the 25th of March. Despite this adjustment, the official start of the year remained January 1, a tradition maintained for historical reasons, particularly to coincide with the start of the consular year .

   To keep the equinox fixed on March 25, astronomers calculated that one year contained 365.25 days. Under this system, a normal year consisted of 365 days, with an extra day added every four years (leap year).

   However, this calculation was slightly inaccurate, causing the equinox to drift backward over time. By the year 325 AD, the equinox had shifted to approximately March 21.

   Interesting Fact: The reason Easter is linked to March 21 originates from the First Council of Nicaea in 325 AD . This council set the rule that Easter would fall “On the Sunday which follows the 14th day of the Moon which reaches this age on 21 March or immediately after that” (e.g. Levy, 1974, La date de Paques, in Annuaire du Bureau des Longitudes, Paris). This firmly established March 21 as a reference point for the equinox.

   For more details about the alignment with March 21, check out this resource .

2. The Gregorian calendar 

   Since March 21 was essential to the Christian Church for calculating the date of Easter — and by the 16th century clearly visible was no longer aligned with the March equinox — the Gregorian calendar was introduced in 1582 AD by Pope Gregory XIII, head of the Roman Catholic Church.

   To correct the drift caused by inaccuracies in the Julian calendar, 10 days were removed from the calendar in October. As a result, Thursday, October 4, 1582, was immediately followed by Friday, October 15, 1582. A period sometimes referred to as the “10 days of darkness”.

   Despite this adjustment, several key elements were retained:

   • The year still began on January 1.
   • The March equinox was fixed to March 21.
   • The average year length was recalculated to 365.2425 days by refining the leap year pattern.
   NOTE: The Gregorian calendar was not adopted worldwide at once. Different regions transitioned to the new system at different times, which can sometimes cause confusion when interpreting historical dates. To accurately determine the modern equivalent of an event from that era, it is important to know where the event took place and whether that location had adopted the Gregorian calendar by that time.

3. The Revised Julian calendar 

   The Revised Julian calendar was introduced in 1923 AD. Although not widely known, it is currently the most accurate calendar for keeping the March equinox fixed on March 21, ensuring equal day and night (12 hours each).

   This calendar was co-designed by Milutin Milankovitch, the renowned scientist behind the Milankovitch cycles (discussed in the previous chapter and appendices). The average year length was recalculated to 365.2422222 days by refining the leap year pattern.

   Despite its accuracy, only a few Orthodox countries have adopted the Revised Julian calendar. While it is not yet in widespread use, I believe it represents the most correct approach to aligning our calendar with natural cycles.

Additional information: Astrology

While digging into the origins of the calendar, I ended up stumbling across astrology. It’s always interesting to imagine how our ancestors might have seen and made sense of the universe. I thought I’d share a few cool observations with you.

To remember all the stars we see around us, ancient astronomers grouped them into constellations, which is kind of like cosmic connecting-the-dots. These constellation shapes represent different kind of object, people and animals to random objects. Some well-known ones include:

• Orion, the Hunter.
• Cassiopeia, the queen and mother of Andromeda.
• Taurus, the Bull.
• Cygnus, the Swan.
• Lyra, the Lyre (basically a fancy harp)

These star patterns weren’t just for navigation purpose only. They were part of the culture to tell stories that helped to connect people to the mysteries of our universe.

1. Why does the zodiac-sign of Pisces start astronomically on 21 march but we call it Aries?

   According to mainstream science, the origin of western astrology started with Babylonian astrology around 2000 BC . I think it started much earlier.

   Since humanity decided to stick with a solar calendar, Earth’s axial precession has slowly shifted the zodiac signs over time. As a result, the meanings behind the original zodiac signs are no longer accurate.

   Most people who haven’t dug into the topic assume they “are a certain zodiac sign,” but the truth is, many of them are actually one sign earlier. So, if you thought you were a proud Leo (like me)… surprise! You’re probably more of a Cancer type☺

2. Why there are 12 signs and not - for instance - 9?

   We can only guess why there are exactly 12 zodiac signs, but it’s likely that our ancestors noticed the four seasons repeating throughout the year. If you were a farmer back then, knowing when to harvest your crops was essential. To keep track, you’d need to divide each season into smaller parts, naturally landing on multiples of 4. Our ancestors chose 12.

   More recently, NASA  suggested adding Ophiuchus as a 13th zodiac sign. But honestly, that feels a bit arbitrary. It all depends on where the lines of the zodiac borders are drawn. I say let’s just stick with the 12 we know and love.

3. What’s the origin of Fire, water, earth and air?

   The four elements  seem closely tied to the four seasons. In the Northern Hemisphere, it could make sense to associate winter with air, spring with fire, summer with earth, and autumn with water. This concept also appears in systems like the medicine wheel .

   However, since the seasons are reversed between the Northern and Southern Hemispheres, this division doesn’t fully align worldwide. The only logical solution would be to create two cycles of the four elements, one for each hemisphere.

   While the origins of this system may have been rooted in seasonal changes, living in a world where the seasons run opposite to each other on different sides of the equator means the concept no longer serves much practical purpose.

   But then again, I might be totally wrong. If one of the readers has a better explanation I am open to it.

4. What is the origin of Cardinal, Mutable and Fixed zodiac signs?

   The three qualities  seem to reflect different stages within the four seasons: increasing, fixed, and decreasing.

   These qualities likely originated from observing the changing months within each season. And unlike some older systems, this one still feels relevant and useful today!

In this chapter, I’ve tried to highlight the consequences of the historical choices we’ve made regarding our calendars. Despite advancements we have yet to implement the most accurate one.