Countries follow astronomical calculations to determine future dates of the Islamic calendar, and this year the Islamic year will be 1437 AH In 2015, that date falls on 13 October.
The holiday has different significance for both Shia and Sunni Muslims.
Muharram is a solemn holiday for Shia Muslims, one they mark by mourning for the first ten days. During this time, they don black attire and participate in mourning gatherings, visiting mosques and shrines with their relatives to remember Husayn ibn Ali. Husayn ibn Ali was the grandson of the Prophet Muhammed and was martyred in 680 CE at Karbala, currently in Iraq. The tenth day is known as the Day of Ashura.
For Sunni Muslims, the tenth day recalls when Moses led the ancient Israelites out of Egypt. Some Muslims fast during the hours of daylight on specific days of Muharram to commemorate that Noah left the ark and that God saved Moses from the Egyptians.