Christian calendar is derived from Roman calendar. Julius Caesar in 46 BC introduced the calendar having 12 months. It started from March 1. Name of months had special meanings.
It is supposed that modern calendar came in three stages. First stage by Julius Caesar
who made the month alternatively 31 and 30. Last month is made of 29 days to get 365 days a year. Second stage by Emperor Augustus , who changed the month August of 31 days and changed 30 and 31 alternatively the month later than that. February is again of 29 days to make 365 days in a year. The third stage may be by Christian followers who changed January from 30 to 31 days, then last month February is of least days, and 29 in leap year.
There is another view that every Era starts with some fixed base. Bikram Sambat has two views. First, 1 Baisakh is the vernal equinox day i.e. equal day and night day, which is governed by by Dinman. Second, Baisakh 1is the day when the Sun enters Aries zodiac at the moment of sunrise. But some think that vernal equinox day is the day when the Sun enters the Aries zodiac. But vernal equinox day is neither Baisakh 1nor 21March, it falls on Chaitra 4 or 17 March.
From first Arya thesis, a year is equivalent to 365.2586 days. The orbit is divided into 12 equal parts of 30 degree each as zodiac. The value of angular velocity is given to all the weeks from the first day of the year. The velocity is different from week to week but when it was fixed is unknown. But it seems the velocity is more than given, so that year equivalent day is less. Because of that vernal equinox is shifting nearer and nearer.
Roman calendar was started from 1 March in 46 BC. It seems it started from vernal equinox with 365 days a year. Leap year is not counted for 100 years. The year divisible by 4 is the leap year, probably from 50 AD started in Christian calendar. After that Christmas day is marked as new year day. But in 12th century, the lady day 25th March was taken as new year day. Probably it was done to adjust vernal equinox day. In 1582 AD, Pope Gregory 13th amended the calendar according to which a year divisible by 4 is a leap year, but a year exactly divisible by 100 is not a leap year, but again exactly divisible by 400 is a leap year.
It was used in Scotland in 1600AD, but it was used in whole Britain in 1752AD only by changing 3rd September as 14th September because 17 century means less by 17 days but 4 more because divisible by 400. 17-4=13 leap year day is subtracted making 3rd September as 14th September. From this very year, January 1st was celebrated as new year day. May be from this very year, 21st March was taken as vernal equinox day. From that time onward no amendment is done.
Fixed days month is so simple that any school boy remembers that - 30 days have September, April, June and November, all the rest have 31 days except February which has 28 days and when leap year comes it has 29 days. It is very easy for calculation involving days as interest calculation and other. Because of this, fixed day month is in use everywhere as date automatically as in watch, mobile, computer and laptop also. It is not possible to do so in Bikram Sambat.
It was mostly used in western countries because they did not consider lunar calendar. They are not aware of using tithi for religious festival and cultural activities. But it cannot be used in our country because our entire nation relies upon a culture that depends upon lunar month tithes. We celebrate birthday not on the basis of date but on the basis of tithi. In the same way, all the religious festivals depend upon tithi.
What is the difference between Nepal Sambat lunar calendar and Bikram Sambat lunar calendar? The position of moon, next day of new moon (Aunshi) pratipada, lies in a certain zodiac that will be the start of corresponding month. For example, Kachhalatho pratipada is the moon lying in Libra zodiac. There is 13th month Anala once in three years.
Name of the month is taken from climatic condition or culture of the corresponding month.
In Bikram Sambat, the position of moon, next day of full moon (Purnima) pratipada Krishnapachhe lies in certain zodiac will be start of the month. For example, Baisakh Krishnapachhe pratipada moon lies in Libra (Tula) zodiac and it is the start of Baisakh 1st. In the same way, as in Nepal Sambat it also has 13th month called purusotam mahina. The names of the month were derived from Nakshetra’s names.
Similarly, there is a difference between Bikram Sambat solar month and Christian calendar solar month. In Bikram Sambat, entrance of Sun to a particular zodiac at sunrise instant is the start of corresponding month. For example, Sun entering Aries zodiac at sunrise instant is the start of first month Baisakh i.e. new year day.
But in Christian calendar, there is no dependence on Sun or Moon position. The days in a month are fixed. May be Jan 1st is fixed among a certain group of stars. But at the beginning of this calendar probably 1st day or new year March 1st was the vernal equinox day.
March 21st was said to be vernal equinox day and a year equivalent is 365.2425 days. But now vernal equinox day i.e. equal day and night day is shifted to 17th March which means actual year equivalent days may be little less than that. May be there is some change in distance between the Sun and the Earth or orbital velocity, which seems Earth came a little closer to Sun increasing the temperature on the Earth. It may be the cause of global warming.
It may be due to decrease in the mass of the earth due to artificial satellite and shuttles to moon, Venus, Mars and Jupiter.
In patra, the position of Sun is given in zodiac with its angular velocity per day. But actual position of Sun is said to be only after adding ayenamsha to that. Ayenamsha is the movement of sun which is very small and equal to 57.45 second angle per year. It is said that 444 Saka Sambat, 579 Bikram Sambat or 523 AD Ayenamsha was adjusted and made equal to zero in this year. From that time onward it was not adjusted. May be Christian new year was made 25th March or lady day from this year too. But now it has accumulated to 24 days.
Hence Baisakh 1st is not the correct entrance of Sun in Aries zodiac, but it enters 24 days earlier. So Baisakh 1st should be shifted 24 days earlier i.e. 24 ansha of the zodiac must be added to every Sun position written in the patra.
Lagna for a new born baby is calculated from Sun’s position at the instant of birth adding ayenamsha to the position written in the patra and with the help of eastern watch, which means day started from the time of sunrise. But at last ayenamsha is subtracted again to get Lagna, which is not understandable. Lagna is supposed to be counted with the help of ayenamsha. So lagna being different, everything or the basis of astronomy is not correct. Can it be a point of attention to be taken for making Chinha of new born baby? With this change everything that is forecasted about the baby by the astronomer will be false. No one will believe him because the 12 quadrants constructed by them will not be correct for any individual. Hence quick action for the change is expected.
Not only that all religious festivals should be based upon sunrise instant tithi for the whole day which is as before the introduction of new system, which is the astronomical technical basis. Please do not to apply two tithi per day, have the whole days as one tithi.