Why do some months have 30 days and other months have 31 days?

The Julian calendar was the reformed version of the Roman calendar which was based on the number of days in the lunar cycle. The reformed Julian calendar tried to equalize the days. The Roman calendar is a lunar calendar. The number of days in a month was roughly based on on the moon and the time between two new moons which is about 29.5 days, so months were made to be 29 or 30 days long. 29 was considered to be unlucky while 30 was lucky. According to legend, the Julian calendar had alternating months 30,29,30,20,etc. Then Julius Caesar added 1 day to each month except for February to fill out the calendar. Then Augustus Caesar changed August to 31 days to match July.

Source: Google
http://www.astro.uu/nl


Why do some months have 30 days and other months have 31?

There were many different types of early calendars. Many of these calendars were based on lunar cycles. People of ancient times adjusted the calendars to meet their needs. The Christian calendar is based on the Julian and Gregorian calendars of 12 months and 365 days.

Source: Monkeyshines on Health and Science, September, 2002.

http://www.Ebscohost.com.proxy.nl.edu


Why do some months have 30 days and other months have 31?

In ancient calendars, the months were originally calculated as time between two full moons. The number of days required to circle earth is 29.5. In modern calendars, the number of days in a month was not based on the moon. The length of months in a year is 1/12 of a year (28.31 days) and is adjusted to fit the 12 months into a solar year.

Source: Funk & Wagnall's New World Encyclopedia, 2008.