On 15/03/2016 00:33, Weatherlawyer wrote:

Julius Caesar had the court astronomers reckon the length of the year quite accurately and
the year was divided into 10 months. Later this was changed to honour dead people
(not called Februs evidently.)

The Roman year changed from 10 months to 12 long before Caesar's time.

The 10 month year was attributed to Romulus, co-founder of Rome. There
is no real evidence that this was so, but the format of the so-called
Romulan calendar was well documented by Roman writers.

The 7th, 8th, 9th & 10th months were named by their position, which is
why they are SEPTember, OCTober, NOVember & DECember. Interestingly the
first four months had names that are also still familiar - Martius (the
god Mars), Aprilis ('opening'?), Maius (the goddess Maia) & Iunius
(poss. for Juno). The fifth month, QUINtilis, was renamed after Julius
Caesar, and the sixth, SEXtilis, after Augustus Caesar.

The additional two months are said to have been added by Numa Pompilius,
king of Rome (715-673 BC). The 10-month calendar had consisted of 304
days, with each month being either 30 or 31 days long. The days between
the end of December and the beginning of March were termed 'winter days'.

Romans considered even numbers unlucky, so Numa removed one day from
the six months of 30 days, and combined them with the 51 winter days
to form Ianuarius (29 days) & Februarius (28 days). These were
originally added as the 11th & 12th months, but Jan 01 later became the
first day of a new year (poss. by Julius Caesar). Ianuaris may have been
named for Janus or Juno, while Februarius may come from februum (a thing
used for ritual purification).

Quintilis was renamed Julius after Caesar's death in 44BC - it was
chosen because it was his birth month. Similarly Sextilis was renamed
Augustus in 8 BC, while Augustus was still Emperor.

Julius Caesar oversaw changes in 46 BC, which were introduced in 45 BC
and are now known as the Julian calendar. It fixed the year as 365 days
with the extra leap day added every four years (Feb 29). This was still
only an approximation of the solar year and the difference between that
and the calendar increased to ~11 days by the time Pope Gregory
introduced the Gregorian calendar in October 1582 - Thu Oct 04 was
followed by Fri Oct 15. The changeover took place in different countries
at different time, with Britain changing in 1752, and, most-recently,
Greece in 1923.

The Gregorian calendar removed the leap day in years which were
divisible by 400, so far only 1600 & 2000.