The way things are in this day and age, we consider summer to start on the summer solstice which occurs about the 21st or 22nd day of June each year. The advantage of doing this is that the seasons are consistent and always start the same time of year. Because the sun takes 364.25 days to circle the earth any calendar based on an equal number of days would slowly shift the seasons into a different part of the year.

Basing a calendar on lunar patterns would also cause problems. Some cultures have tried it but since the moon takes about 29 and a half days to circle the earth that too means that major adjustments need to be made of the seasons would move out of when they should be.

So, for simplicities sake we base our seasons on the soltices and equinoxes. Tomorrow, my solution for a calendar.