Angle

January 27, 2010, 7:24 am • Tags: , ,

icon_40In the Indian Hindu calendar, Tithi is the lunar date. A tithi is the time taken for the longitudinal angle between the moon and the sun to increase by twelve degrees. Tithis begin at varying times of day and vary in duration. As the moon rotates around the earth, the angular distance between the sun and the moon as seen from the earth increases from 0 degrees to 360 degrees. A lunar month consists of 30 tithis, whose start time and duration vary. 

The lunar date, however, varies approximately between 22 to 26 hours based on the angular rotation of moon around the earth in its elliptical orbit. It takes one lunar month or about 29.5 solar days for the angular distance between the sun and the moon to change from 0 to 360 degrees. When the angular distance reaches zero, the next lunar month begins. Thus, at the new moon a lunar month begins; at full moon, the angular distance between the sun and the moon as seen from the earth becomes exactly 180 degrees. 

Since the angular distance between the moon and the sun is always relative to the entire earth, a lunar day or tithi starts the same time everywhere in the world, but not necessarily on the same day. Thus, when a certain tithi starts at 10:30pm in India, it also begins in New York at the same time, which is 12:00pm on the same day. Since the length of a tithi can vary between 20 to 28 hours, its correspondence to a weekday becomes a little confusing. 

Tithi is one of the most important aspects of the Indian Almanac, or Panchang, and therefore many Hindu festivals and ceremonies are based on the Tithi Calendar. Most Indians celebrate Kartik Shudha Prathama (the first day of the Indian lunar month Kartik) as their New Year’s day. Indians living in India, Europe, and the eastern part of the United States thus celebrate their New Year on that Monday, while regions west of Chicago do so on the preceding day, Sunday.