What is a day? Many would think the answer is obvious. Many would say 24 hours. But the scientific truth is you have ask a particular question first, “On what planet?”
You see: on Venus a day is 5,832 hours; a day on Mercury lasts 1,408 hours; on Mars a day is 25 hours; and on Jupiter it’s 10 hours. One of the reasons is that a day depends on the position of the planet during its orbit around the sun, the shape of the planet’s orbit, where you are positioned within the planet, the length of time it takes a planet to spin around its axis and the date of observing time in the history of the universe. So for instance the orbit of the earth around the Sun is elliptical and during certain times of the year a day is either longer than 24 hours or shorter than 24 hours. Also if you are based at either the south pole or the north pole a day can last as long as six months.
Over time, some planets are losing momentum. So a day on earth is becoming longer as time elapses by about 1.7 milliseconds per century (an average over the last 2,700 years).
What is a year? 304 days, 360 days or 365 days? Or 365.242 days? Again, a year depends on what calendar you are using and why you are using it. The calendar we all use today is the solar calendar and it was devised in Egypt.
The calendar as devised in Egypt had a religious, political and agricultural significance. The ruler of Egypt was believed to be a representative of the gods, and the inundation (flooding) of the Nile was believed to be a judgement by the gods of the ma’at – the right standing – of the ruler of Egypt with the gods. If inundation (akhet) happened at the beginning of the calendar, the Pharaoh had led righteously, if the inundation didn’t happen the Pharaoh had led either immorally or unwisely.
It was not enough to unify many smaller kingdoms into one political state. To retain power each monarch during the long period of existence of the Egyptian political structure (3,200 BCE to 300 BCE) had to keep the basic need of their subjects met for a predictable food supply.
The inundation started in July and resulted in the Nile depositing silt and water in particular areas to facilitate productive plant cultivation by the Egyptians. Although pre-dynastic Egyptians started observing the stars around sixth millennium BC at Nabta Playa by about 4,236 BC, the Egyptian had worked out that the inundation, the best time for their agricultural year to start, was most accurately marked by the helical rising of Serpet (the star “Sirius” in English). There is evidence Sirius could have been observed from Nabta Playa around 6,088 BCE.
With a start date for the year selected, Egypt then had to pick between a lunar calendar, a Sothic calendar on a 1,461 year cycle and a solar calendar, in which one year represented one orbit around the Sun by the earth. The Egyptians chose to keep all three. Thus, began the use of a 365 day calendar.
If you were to guess who invented the 365-day calendar, most people might say the Romans, some might say the Greeks, still others might say Mesopotamia. All three guesses would be wrong.
The Romans only started to have a world influence during the 3rd century before our era. They started off using a lunar calendar based on 10 months and 304 days introduced by Romulus, the founder of Rome. Even when Pope Gregory introduced the Gregorian calendar, it wasn’t to create a more accurate calendar. A 365-day calendar had already been invented. The Gregorian calendar was introduced to decide Easter more easily.
The first month in the original calendar introduced by Romulus was March. March came from the Latin Martius mensis meaning the month of the god Mars; the first month of 10 months in a year.
April came from Aprilis in Latin – the month of Venus (being Aphrodite in Greek and Aphrilis in Latin). Easter is the first Sunday after the spring solstice and comes from Eostre in Mercian dialect of old German, or Eastre-Monap in Anglo-Saxon. The Christian paschal month replaced feast of Eostre.
June came from mensis Junius which contained the summer solstice and a series of events. By day: on May 29 to June 1 Festival of Ludi Fabarici, on June 1, Kalendae Fabariae, on June 3 Festival of Bellona, on June 7 Ludi Piscatorii and on June 7 to June 15 Vestalia, on June 20 Rosalia. Every 100 years, the Secular Games was held in either May or June.
July was named after Julius Caesar, after deification for conquering France, parts of Germany, Spain, Egypt, suppressing civil wars, and conquering parts of Turkey and Syria. This month was formerly Quintilis, the fifth month.
August was named after Augustus, for being one of the best emperors Rome ever had. To be August is to be divine. This month was formerly memsis Sextilis, the sixth month.
September is from Latin for the seventh (Septem) month (-ber). October is from Latin for eighth (Octo) month (-ber). November is from Latin for ninth (Novem) month (-ber) and December from Latin for the tenth month.
So where did January and February come from? The 10-month calendar did not really work well for farmers and planting. The second king of Rome, king Numa Pompilius, added 2 months.
Januarius, written mensis Januaris, meant the month of either Janus or Juno. Janus was the god of beginnings, gates, transitions, time, duality, doorways, passages and endings. He is sculpted with two faces on one head. One face looking to the past and another looking to the future.
Februarius comes from Februum, a month of ritual purification. Events included Parentalia – a nine-day festival to honour ancestors and propitiate the dead – and Terminalia – a set of rituals to close off the year, and mark this with boundary stones. The tutelary deity of February was Neptune, according to the farmers almanacs.
The Romans had an Intercalaris, an intercalendar month. This month had 27 days until abolished by Julius Caesar. It was also known as Mercedonius. It was added every fourth year to fix the errors in the previous years. With the intercalaris removed, Julius Caesar moved the start of the year to January instead of March and changed the number of days in each month.
The word calendar comes from Latin, meaning to “call”. This related to an annual ceremony in which the Pontiflex, the high priest of Rome, announced the start of a new year. A little known fact is that Julius Caesar held the post of Pontiflex Maximus prior to his military career and world travels, which included a trip to Egypt to defeat Mark Anthony (Marcus Antonius) and Cleopatra. This may have explained his involvement in fixing the Roman time-keeping system.
The Greeks originally according the Eleusinian Mysteries of the Mycenean period (1600 – 1100 BCE) used the Attic calendar in the administration of an agrarian cult – an agriculture focused religious system or political philosophy. The Attic calendar was not used outside of Athens. Not many scholars understand how it really worked and what changes occurred to the calendar system during the period of its use because the Greeks didn’t have writing before the sixth century BCE. Within Ancient Greece, no fewer than fifteen different calendars were developed, all mostly based on 12 lunar months, with no intercalary month to fix the difference between 365 days and measurement of a year by those calendars.
In this time before our era, it becomes clear how Persia after conquering Egypt, the Greeks after conquering Egypt and the Romans after conquering Egypt fixed their calendar issues using the brilliance of the Egyptians. While we now know a lot of complex facts about what a day is, how the earth orbits the sun, what a year is and that a year is different across various planets in the solar system, it is remarkable that the ancient Egyptians were able to invent a calendar that we are still fundamentally using today. Although we now measure a year more accurately, the 365-day calendar without leap years developed by the Ancient Egyptians only produced an error of 25 days during their entire history. Today, you are probably using this African calendar to mark time.