The Brahma Purana says that it was on Chaitra (month) Shukla (phase of the moon) Pratipada (first day of the lunar month) that the universe was born, and it was on this day that Lord Vishnu incarnated for the first time. Thus, time began to be calculated from this day. The earliest traces of Indian chronology or science of time and chronometry or scientific measurement of time belong to the Vedic period, which was later developed by astrologers like Aryabhata, Varahamihira, Bhaskara, etc.
The Indian Sanatan tradition was formed in harmony with nature. Information about the speed or velocity of celestial spheres and the calculation of time was first calculated in India. However, it is the moon’s movement that determines the Hindu Calendar instead of the sun which determines the Western calendar (also called the Gregorian calendar). According to the Gregorian calendar, the New Year begins after 12 am on December 31. But the New Year in the Hindu calendar begins on the first day of the Shukla Paksha of the Chaitra month.
The date of the panchang can start at any time in the day or at night as it is directly related to the visit of the moon to the nakshatra. From Chaitra Shukla Pratipada, the days begin to get bigger than nights. And, the worship of Shakti begins with Chaitra Navratri (the nine days that follow).
The 30 days of the month are divided into two sets of 15-15 days based on the moon’s phases – Shukla Paksha and Krishna Paksha.
A month in the Hindu calendar is a complete lunar cycle of the moon’s waxing and waning. They are called Shukla Paksha (waxing or brightening) and Krishna Paksha (waning or darkening). Thus, each lunar month is precisely 29.5 days long. Some people mark a full-moon night as the month's end, while others end their month on a no-moon night. The first is called Purnima, and the latter is called Amavasya. It is believed that Shukla Paksha is suitable for good deeds while the dark nights of Krishna Paksha are not good to do anything new or auspicious.
Lunar days in a Hindu calendar are called tithis, which are calculated mathematically by checking the difference between the longitudinal angle of the sun and the moon. As the time of the sun’s rise changes, tithis vary in length; sometimes, a tithi gets dropped, or two consecutive days share the same tithi at certain times.
The lunar calendar has 12 months, each comprising 29.5 days; 29.5 multiplied by 12 adds up to 354 days, so a year calculated in this way is smaller than the solar calendar, which has 365 days, by 11 days. All the dates in the Hindu calendar are moved back by 11 days every year to sync both calendars. An extra month called adhikmasa is added once about every two-and-half years.
The names of the lunar months are Chaitra, Vaishakha, Jyaishtha, Aashadha, Shravana, Bhadrapada, Aashvayuja, Kartika, Margashirsha, Pausha, Magha, and Phalguna.
The sun and the moon, traveling through various constellations, give us the solar and lunar zodiac signs. Your solar zodiac sign is when the sun is traveling through a particular constellation. Similarly, if the moon travels through a specific constellation when you are born, that is your lunar zodiac sign or Rashi.
There are 12 lunar zodiac signs: Mesha, Vrishabha, Mithuna, Kataka, Simha, Kanya, Tula, Vrishchika, Dhanus, Makara, Kumbha, and Mina.
The name of the lunar month depends on the transit of the sun. As it transits into a Rashi, a new month begins from that day. For instance, when the Sun enters Mesha Rashi, the lunar month is named Chaitra, and when the Sun enters into another Rashi, the lunar month accordingly changes.
The Hindu Vedic calendar and all the festivals are based on this lunar monthly classification.
