I stumbled across this today and found it rather interesting. Espescially as there is sometimes controversy over the Nisan 14 date.
Paschal Full Moon.
Refers to the Ecclesiastical Full Moon of the Northern Spring to determine the date of Easter
A full moon is a lunar phase that occurs when the moon is on the opposite side of the earth from the sun.
The moon is in opposition with the sun.
Babylonian Astronomy.
According to Asger Asaboe - the origins of Western Astronomy can be found in Mesopotamia and all Western efforts in the exact sciences are descendants in direct line from the work of the Babylonian Astronomers.
Chaldeans were the Astronomers of Mesopotamia, who were, in reality, priest scribes specialising in Astronomy and other forms of divination
(taken from wiki )
There is a lot more information on this and it's Pagan Babylonian Origins.
Considering WT teachings focus heavily on 'False Religion' and Babylon, I find it odd they co-ordinate the memorial dates to the Paschal Full moon and Astronomy.
Things we are warned to stay away from.
Amazing the things we can find when we have the freedom to research them.