1. The length of the solar year of the Bikrami Samat does not conform to the tropical year length. The Bikrami year is sidereal year of 365 days, 6 hours, 9 minutes and 10 seconds. The tropical year on which the Common Era calendar is based, has its length as 365 days, 5 hours, 48 minutes and 46 seconds. If the months of any given Era are to recur consistently in the same seasons, then the year length has to be that of the tropical year. This difference of 20 minutes or so in the two types of years is because of the precession of equinoxes, the yearly retrograde motion of the first point of Aries of the ecliptic. Over a period of time, this difference builds up, and shows in those calendars, which are not based on the tropical year. The seasons in relation to the months begin shifting. This is the reason why Vaisakhi has shifted by 8-9 days from 1469 CE to the present times. The Vaisakhi dates for certain epochs are as follows :
CE Year Vaisakhi Date
1000 22nd March
1469 27th March
1699 29th March
1752 29th March
1753 9th April (due to change from Julian to Gregorian Calendar)
1799 10th April
1899 12th April
1999 14th April
2100 15th April
If Nanakshahi calendar is not de-linked from the Bikrami calendar, this shift will continue, and in 13,000 years Vaisakhi would occur in the middle of October. The seasons will be opposite to those, which are mentioned in the Barah Maha Majh, and Tukhari Banis.
2. The days in the months are not fixed. The number can vary from 31-32 days for the summer months and from 29-30 days for winter months. The rules for determination of Sankrantis, beginning of the months, is complicated and public have to rely on Jantri publishers for such a simple thing as the beginning of a month.
3. The lunar portion of the calendar, according to which most of the religious festivals are fixed, has its share of peculiarities. Since it is based on 12 months of the lunar cycle (full moon to full moon or new moon to new moon), its year length is about 11 days shorter than that of the solar year. Therefore, its year begins 11 days earlier in the following year in relation to the solar year. This is why the Gurpurb dates shift by about 11 days from one year to the other. This is not the end. To keep the lunar year in step with the solar year, every two or three years an extra month is added to the lunar year. This month is called malmas or intercalary month. That lunar year contains 384 or so days. This makes the Gurpurb dates to occur by about 18 or 19 days later when such a month is introduced. The month of Jeth that will occur in 1999 CE will be intercalated, i.e., there would be two months of Jeth, one Sudha and the other Mal. In the malmas or the extra month religious festivals are not celebrated. This is quite a complicated set up, and is also contrary to the philosophy of Gurbani according to which no month in itself is good or bad. The festivals and Gurpurbs that are celebrated according to the lunar calendar are called movable, and those that are celebrated according to the solar calendar are called fixed. The movable festivals are called as such, because their dates are not fixed in relation to the solar year. From year to year they occur on different dates of the solar year, though their lunar date is the same every year. Gurpurbs of the ten Patshahis are all movable. Vaisakhi and Maghi are fixed festivals. An example of movable celebration is the Parkash Gurpurb of Guru Gobind Singh. It is celebrated on the 7th day of the bright half of the lunar month of Poh (Sudi 7). This lunar date occurs on the following dates of the Common Era and Bikrami Era (solar) during the following eleven years:
CE Date Bikrami Date CE Date Bikrami Date
24th Dec., 1990 10th Poh, 2047 12th Jan., 1992 28th Poh, 2048
31st Dec., 1992 17th Poh, 2049 19th Jan., 1994 6th Magh, 2050
7th Jan., 1995 24th Poh, 2051 28th Dec., 1995 13th Poh, 2052
15th Jan., 1997 3rd Magh, 2053 5th Jan., 1998 22nd Poh, 2054
25th Dec., 1998 11th Poh, 2055 14th Jan., 2000 1st Magh, 2056
This Gurpurb did not occur in the CE years 1991, 1993 and 1996. It will not occur in the year 1999 (the year of 300th anniversary of the creation of the Khalsa). It occurred twice in 1992 and 1995; and it will occur twice in 1998. According to the Bikrami calendar (solar) the date of Parkash of Guru Ji is 23rd Poh, 1723 BK. During the above period Gurpurb does not occur on that date. Rather, it occurs in the month of Magh in three years.