Here is an easy thumb-rule, which helps one to keep track of the phase of the moon or the Tithi. One has to just add the date and the corresponding number of the month of the international calendar. For April 2nd one has to add 2+4 (4 for the month of April). There is also a lunar number for the year. For 2007, this number is 9. So, let us add all the numbers now: 2+4+9 = 15. This signifies on April 2, 2007, the Moon is 15 days old, i.e. it is a full moon day or Shuklapaksha Pratipad.
Before carrying out this simple calculation one has to remember that a 30 day old Moon is a New Moon once again. So, 30 should be subtracted if the added number comes out to be greater than 30.
The same calculation can safely be carried out for other days and months, and you will be never be more than two days off from the Tithi of that date.
However, the lunar number will change for the next year. It always increases in steps of 11. So, for the next year the corresponding number becomes 9+11 = 20 and for the subsequent year, i.e. 2009, it becomes 20+11 = 31 = 01. The same counting rule applies here also as mentioned earlier. There is however, nothing sanctimonious about this lunar number. One may adjust this number according to his or her convenience to get a closer to the correct result.
Try this out yourself, and you will find how much fun it is to explore the simple hidden laws behind the natural events around us.
