Why Ramadan starts eleven days earlier every year.
The Islamic calendar is purely lunar: twelve lunar months add up to about 354 days, eleven fewer than the solar year. There are no leap months to compensate. So the fasting month of Ramadan drifts backwards through the seasons, cycling through the whole solar year roughly every 33 years. Midsummer fasting means up to 19 hours without water in Scandinavia.
Useful: Islamic holidays cannot be pinned to a fixed date in the Gregorian calendar.
Source: en.wikipedia.org