Updating the Bikram Era Calendar of Nepal

Kedar Sharma, Galileo Astronomical Society, Pokhara, Nepal.

Two millennia have passed since the inception of the Bikram Era (BE) calendar, and the time has come to update it due to the effects caused by the precession of the equinoxes. This calendar is being used both in Nepal and India. In Nepal it is being used by the government and religious communities In India it is used only by religious communities, for the government of India uses the Gregorian Calendar. Modern astronomers and traditional astrologers in both Nepal and India agree that the BE calendar needs to be updated, but who is authorized to update the calendar is not clear. But before all this, let's analyze the scientific reasons that contributed to the necessity of updating the calendar.

The Earth has three types of motions: motion around its axis, motion around the Sun, and motion of its axis due to wobbling of Earth. The Earth rotates around its axis in 24 hours, which causes day and night. In the Northern Hemisphere we see that all but one of the stars and planets rise in the east and set in the west. The one star that does not rise or set is the polar star (Dhruv Tara or Polaris), which is located directly above the Earth's North Pole. The Earth is tilted 23.5 degrees on the plane of orbit around the Sun. This causes changes of seasons during the year.

The second type of motion is the rotation of the Earth around the Sun in 365 days to complete one revolution in an elliptical orbit. Speaking more precisely, the Earth takes 365 days, 6 hours, 9 minutes and 10 seconds to complete one revolution with respect to the stars (sidereal year). With respect to the orbit, it takes 365 days, 5 hours, 48 minutes and 46 seconds to complete one revolution (tropical year). The difference in time is 20 minutes and 24 seconds. This is caused by the third type of motion of Earth, the wobbling of its axis, which astronomers call precessional movement of the pole of the Earth. (See Fig. 1.)

Two Systems of Astronomy in South Asia

There are two systems of astronomy in South Asia, namely the Nirayana (sidereal) and the Sayana (tropical). The former traces observations of planets to a fixed zodiac, while the latter considers the moving zodiac commencing from the shifting Vernal Equinox. The increment between the beginning of the "fixed" and the "moveable" zodiacs or the Nirayana and Sayana positions, is referred to as Ayanamsa, which increases about 50 1/3 seconds every year. This means that in every 2,150 years, the equinoxes arrive one month ahead. The Ayanamsa for the year 2005 is 23 degrees 53' 18" (or 24 days).

Since the time of inception of the BE Calendar, equinox points have moved backwards, i.e. the spring equinox falls on Chaitra 6 instead of Baishakh 1. The difference between the sidereal zodiac and the tropical zodiac is called an Ayanamsa, a term of Vedic astrology. If you know the Ayanamsa, it's easy to change a tropical position into a sidereal position, or the other way around. Add the Ayanamsa to the sidereal position to get the tropical position. And subtract the Ayanamsa from the tropical position to get the sidereal position.

The Bikram Era Calendar

The Bikram Era calendar is based on the sidereal year whereas the Western Gregorian calendar is based on the tropical year. Sidereal calendars need to correct 1 day in 70 years, as seasons come one day earlier after that period. This motion is very slow and can be detected only after observing for hundreds of years. Therefore people generally don’t take this motion into account. But for making calendars, consideration of this motion is vital. As the Earth wobbles around its axis in 25,791 years, the position of the celestial pole also changes at 50.33 arc seconds a year around the ecliptic pole. Due to this, points of equinoxes also change. And after a considerable time, we see the seasons also changing. This is called the precession of the equinoxes, i.e. the arrival of equinoxes earlier as time passes. This doesn't apply to the Gregorian calendar, as it is based on the position of Earth in its orbit around the Sun, and the position of stars is not taken into account.

As the Bikram Era Calendar is not updated for two millennia, the precessional effect has already accumulated to 24 days. This means that Maghe Sakranti (winter solstice) actually falls on Poush 7. Similarly the new year (spring equinox point) falls on Chaitra 7, instead of Baisakh 1. If the Bikram Era calendar is not updated, it will soon loose its seasonal relevance. This will also affect the celebration of festivals, as many of our festivals in Nepal are associated with the arrival of seasons. It is expected that concerned authorities in Nepal will take necessary steps to update the BE calendar. But before doing this, the general public should be properly informed on the need to update the calendar, both in Nepal and India.

Recommendations

1. Chaitra 1 should be made the start of New Year. Lunar month should also be moved 1 month ahead.

2. The start of a new day (i.e., time counting) should be from 12 PM at midnight, as practiced internationally.

3. The Panchanga should be made user-friendly. So far traditional astrologers mostly use it. But in future it should be made useful to amateur astronomers as well. For this the positions of celestial bodies should be given in RA and Declinations. The Ghati-Pala-Bipala system should be replaced, as this system is no more in use to keep time.

4. Ayanamsa (precession) should be updated each year by adding 50.33 arc-seconds each year.

5. Traditionalists should be encouraged to use telescopes to track the correct positions of celestial bodies. Telescopes should be made widely available in the country.

6. Traditional instruments (Dhup Dhadi, Chhate Duhuga/ Stonehenges, etc.) and methods of determining the positions of celestial bodies should be revived so that ancient knowledge is preserved. The Balmiki campus could take a lead role in this.

7. Traditional astrologers believe that the precession oscillates between +27 degrees to –27 degrees based on the Surya Siddhanta. However, modern astronomy believes that it moves along the whole circle. Research on this difference of opinion about this key issue should be made and resolved.