Man sees crescent of the moon by himself. Two equitable witnesses testify. Islamic judge announces that the new moon has begun or finished. If proving of new moon was doubtful, man should not fast as Ramadhan. Since intention is necessary in other worship, the fast needs intention too, so the fast without intention is not acceptable.
Intention means that a man intends to fast and avoids of things which break fast.
Enema Vomiting A woman who is menstrual irregular discharges has to do ritual ablution for prayer. If she does not do so, her fast won't be acceptable. If a person didn't fast for sickness or travel and etc, in Ramadhan month, he must do fast-compensation after Ramadhan. His opportunity will be till next Ramadhan. He must not delay his fast compensation more than one year.