The 10th Day and The 14th Day
After 400 years Israel and Egypt were on the same page for a common calendar. If Israel was told to do something on a certain day all would know what day and Israel would do as they were told with no misunderstanding as to what day was intended. Egypt had a lunar calendar and a solar calendar that worked as a unit.
The lunar calendar was the older of the two. The lunar month was set when the waning crescent and the disappearance of the moon gave them a totally dark moon to start the month. The day it became dark was the first day.
The solar calendar started the year in the spring with the spring equinox. They celebrated a festival at the base of the pyramid that was set when the spring equinox was in line with the base line of the pyramid. {Sham el-Nessim}
History tells us this was how they set the year and divided it into months and days. Leviticus 23 is a continuation of this method and Israel understood this.
Things have been added with time. Ask, did GOD or man do the adding?
19 year time cycle
Looking for the coming of a crescent moon
Postponement rules
Sanhedrin
Read the article, THE BEGINNING OF MONTHS.
10-27-12, Earl McDowell and Art Ryan.