http://en.wikipedia.org/wiki/Ramadan

"Eid ul-Fitr - From Wikipedia

Main article: Eid ul-Fitr
The holiday of Eid ul-Fitr (Arabic: عيد الفطر‎) marks the end of the fasting period of Ramadan and the first day of the following month, after another new moon has been sighted. The Eid falls after 29 or 30 days of fasting, per the lunar sighting."