When does Ramadan begin? Well, it all depends on when the New Moon is first sighted. We know exactly when the New Moon happened, it was at 05:25 UT (Universal Time, essentially the same at Greenwich Mean Time) on Thursday the 22nd this month.
But, that is not when Ramadan traditionally begins. Ramadan begins at the beginning of the Muslim holy month of Ramadan, in fact the month of fasting is named after the month. Ramadan is the 9th month in the Islamic calendar. Unlike the calendars used in the Gregorian calendar, in the Islamic calendar, the months traditionally start at the first sighting of the New Moon. Not when the New Moon happens, but the first sighting of the New Moon (or, strictly speaking, a crescent Moon).
Of course, by definition, you cannot see the New Moon, because the Moon is between the Earth and the Sun (not directly in line with it unless there is an Eclipse), so in fact to see the “New Moon” you have to wait until the Moon has passed this point by a certain amount, whereupon you can see a Crescent Moon.
So, as the first sighting of the Moon after the New Moon on Thursday the 19th appears to have been on Friday the 20th, that is when Ramadan began this year. Of course, next year, we know it will move forward by between 10 and 11 days, as I explained in this blog.