Guru Nanak, the founder of Sikhism, was born on Puranmashi of Kattak in 1469, according to the Vikram Samvat calendar[10] in Rai-Bhoi-di Talwandi in the present Shekhupura District of Pakistan, now Nankana Sahib. It is a Gazetted holiday in India. The controversial Bhai Bala Janamsakhi claims Guru Nanak was born on the Full Moon (Pooranmashi) of the Indian Lunar Month Kartik. The Sikhs have been celebrating Guru Nanak’s Gurpurab around November for this reason and has it been ingrained in Sikh Traditions.
However, some scholars and organizations believe the Birthday should be celebrated on Vaisakhi, which falls on 27 November according to the original, However, many people and organizations would like to keep the traditional date by celebrating on the Full Moon Day (Pooranmashi or Purnima) of the Lunar Month Kartik. The Nanakshahi Calendar follows the Gregorian calendar and celebrates it on Kartik Purnima. This is a mismatch between different time units. The problem with designing an accurate calendar is that the three natural units of time – the day, the month and the year – are based on different movements – the Earth’s rotation about its axis, the Moon’s revolution around the Earth and the Earth’s revolution around the Sun. Their periods are not integer multiples of each other. The challenge in aligning solar and lunar calendars arises from the discrepancy in their respective durations. A solar year spans approximately 365.25 days, while a lunar month is around 29.53 days. The sum of twelve lunar months falls short of a solar year by 11 days, 1 hour, 31 minutes, and 12 seconds. Over three years, this discrepancy nearly equals one month. The Moon’s orbit takes about 27.3 days, causing it to lag behind the Earth’s orbit around the sun, resulting in a 10.87-day difference between a lunar year (354.372 days) and a solar year (365.2422 days).