why did the ancient astrologists not fix the uniform (30) days in each month?

Answer 1

There's a great summary of the history of the calendar here:

http://www.skeptics.com.au/journal/1995/1_calendar.htm

30 days per month wouldn't work anyway. 30 x 12 = 360, leaving 5.25 days to deal with later.

Answer 2

We have months because the moon (moon => month) takes that long to go through all its phases. Many early calendars were based on the moon, and since the moon takes slightly less than 30 days to complete one cycle, some years had 12 months and some had 13.

To focus on European history, when the Romans came along they figured out that an average year was not 360 but 365.25 days long (and 15 centuries later that was refined to 365.2422 days), so they invented the leap year cycle of 365, 365, 365 and 366 days every four years.

The extra 5 or 6 days in every year were originally distributed as evenly as possible into this newfangled solar calendar, however politics eventually warped it into its present form. July and August are named after Julius and Augustus Caesar, and Augustus stole a day from February so his month would be as long as July, leaving February shorter than it already was.

There have been suggestions to improve on our present calendar by making every quarter look the same, with 3 months of 30, 30 and 31 days (exactly 13 weeks) and beginning on Monday every year [the European week begins on Monday because after all the week*end* is supposed to be Saturday and Sunday, and Sunday is also the "seventh day" in the creation story]. This leaves only one extra day each year, which is added between Sunday, December 31st and Monday, January 1st (the extra leap year day is added at the end of June).

The only thing that might bother some people about this arrangement is the occasional extra days between Sunday and Monday, but the advantage of having a more regular year seems greater than that minor inconvenience. I would improve it further by moving January 1st back a few days to coincide with the winter solstice. Make that day be Christmas and our currently hectic holiday season would be happily shortened too.

By the way, astrologers weren't always with us. Originally in fact their only job was to measure celestial events for the very practical purpose of knowing when to plant the crops, and not to make loopy "interpretations" of how the stars and planets supposedly influenced individuals on earth.

Answer 3

Just a guess, but I don't think they could influence the motion of the plant in relation to the solar system. Variation seems to, simply, exist.