𝐉𝐚𝐧𝐮𝐚𝐫𝐲 𝐚𝐧𝐝 𝐅𝐞𝐛𝐫𝐮𝐚𝐫𝐲 𝐚𝐫𝐞 𝐭𝐡𝐞 𝐧𝐞𝐰𝐞𝐬𝐭 𝐦𝐨𝐧𝐭𝐡𝐬 𝐨𝐧 𝐭𝐡𝐞 𝐜𝐚𝐥𝐞𝐧𝐝𝐚𝐫, they were originally inserted as the 11th month and 12th months of the year on the old calendar. The old Roman year had only 10 months with December as its last month. The root of the word, ‘dec’ is derived from Latin and Greek translating as the number ten. Accordingly, the months after the harvest were simply numbered. Sept/seven, Oct/eight Nov/nine & Dec/ten. The -ber element in four Latin month names is probably from -bris, an adjectival suffix. Therefore, the original could have been decemo-membris from -mensris from mens- meaning ‘month’. Menses and menstruation (monthlies) are also derived from mens.
While the sun gives us our calendar year the moon gives us the months in fact the word ‘month’ is named after the moon. It is a period calculated to be one complete phase of the moon. There are roughly 12 moon phases in a calendar year.
The average calendrical month, which is one twelfth of a year, about 30.44 days, while the Moon's phase (synodic) cycle repeats on average every 29.53 days. Therefore, the timing of the Moon's phases shifts by an average of almost one day for each successive month.
The seven-day week also comes from the lunar cycle due to the four principal lunar phases namely the first quarter, full moon, last quarter, and new moon. Each of the four lunar phases is roughly 7 days or roughly 7.38 days but each varies slightly due to lunar apogee and perigee. The Moon's orbit is fiendishly difficult to explain, so for more information lookup the phrase ‘barycentre’.
Many centuries of observational studies have yielded these figures but in ancient times these abilities lay in the distant future. So the Romans simply counted ten months from the start of their year at the vernal equinox but were flummoxed when deciding to whether or not to add to add two or three months at the end.
Eventually January (Ianuarius) together with February (Februarius) were inserted on the calendar around 700BC. March remained the beginning of the year until 153BC when it was designated to January. This had the effect of shifting the months out of kilter with their literal meanings by two months! Everyone mistakenly believes that his was due to the insertion of July and August. The month Quintilis (5th) was renamed July in honour of Julius Caesar in 44BC and Sextilis (6th) was renamed August in honour of Augustus in 8BC.
So today, we have a lunar calendar superimposed on a solar calendar but the two cycles are not synchronous. Reconciling the two was one of the greatest challenges faced by scholars and was only solved in with the calendar reforms under Pope Gregory in 1582.
January 1st was not universally accepted as the start of the New Year and many countries continued to observe New Year at various times. For example the Byzantine Empire or the old Eastern Roman Empire celebrated New Year on September 1st.
After the fall of the Western Roman Empire the start of the New Year went back to March 25. This date remains the start of the financial new year in many territories including the UK but is now April 5th because 10 days were annulled as part of the Gregorian calendar reforms.
The 1582 calendar firmly place January the first as the start of the New Year. However, many protestant countries were slow to adopt a “Catholic” calendar. Ireland, for example, under the control of Protestant England, held its New Year celebrations on the Feast of the Annunciation on March 25th. It continued up until 1752 when the English finally relented and started using the Gregorian calendar. It should be noted that most countries in Western Europe had officially adopted January 1st as New Year's Day even before they adopted the Gregorian calendar.
History students might be bemused to find that the English parliamentary record lists the execution of King Charles I as having occurred on the 30th of January 1648 and not 1649. 1648 did not end until the 24th of March but historians have retrospectively adjusted the start of the year to 1 January and so record the execution as occurring in 1649.
The month of January is named in honour of the god Janus by the Romans who is the god of beginnings and transitions, thence also of gates, doors, doorways, endings and time. He is usually a two-faced god since he looks to the future and the past. Early Romans believed that the beginning of each day, month and year were sacred to Janus. They thought he opened the gates of heaven at dawn to let out the morning and closed them at dusk. The image here is of a Celtic idol with two faces (Janus form) in Caldragh graveyard on Boa Island in Lower Lough Erne, Co. Fermanagh