A while ago there was a discussion on here about the dates of Easter and the archbishop of Canterbury trying to get it changed so it is fixed. Since then, I've been busy researching for the real reasons why it was decreed nearly 1000 years that Easter would fall based on the first full moon of the spring equinox.
Here's what I found out:
Nisan (or Nissan; Hebrew: נִיסָן, Standard Nisan Tiberian Nîsān) on the Assyrian calendar is the first month and on the Hebrew calendar is the first month of the ecclesiastical year and the seventh month (eighth, in leap year) of the civil year. The name of the month is Babylonian; in the Torah it is called the month of the Aviv. Assyrians refer to the month as the "month of happiness." It is a spring month of 30 days. (Nisan usually falls in March–April) on the Gregorian calendar. In the Book of Esther in the Tanakh it is referred to as Nisan. Karaite Jews interpret it as referring to the month in which barley was ripe.
That above information (courtesy of wikipedia) sounds awfully complicated. So I'll simplify it:
Jesus was Hebrew. He was an Aramaic speaking Jew that observed the Hebrew Calendar and not our traditional gregorian one. Jesus died in accordance with the Hebrew calendar and the month he died was Nisan and the date of the day he died was almost certainly Nisan 15 - namely the festival of unleavened bread or in simpler terms, Passover. Nisan 15 fell on a Friday two times between AD 29 and AD 36 - in AD30 and AD33. Because the month of Nisan is determined by the full moon, if you translate this month (Nisan) into the Gregorian calendar, it ranges between 21st March and 23rd April as it is a 30 day period. So, we have to consider the variations of the date based on the moon and then consider the actuality of when Jesus died within his calendar and not ours.
There, I hope I've given you something interesting to consider!