It happens when the month has 31 days and the 1st is a Friday.
There are 7 months each year that have 31 days. There is a 1 in 7 chance that the 1st will be a Friday. So on average this happens once a year.
Exactly 14.5% of all Aug. 13ths are Saturdays. That makes the average frequency of Aug. 13 falling on a Saturday approximately once every 6.90 years.
Every lunar month. Which is approximately every 28 days.
Once in a blue moon! Well that is what the second full moon in a month is called, a blue moon. It is very irregular, sometimes it can happen multiple times a year or even two months in a row. Other times it can be years between them.
The Full Buck Moon is normally the month of July when the new antlers of a buck deer are in velvet. It was also often called the Full Thunder Moon, because thunderstorms are most frequent during this time.
Astronauts currently work in six month shifts on the international space station. A single astronaut might fly only once in his career. Others, however, have flown as many as five or six times! (Astronaut training is expensive.)
March
ummm...never.
About twice each year
every 823 years.
Exactly 14% of all Decembers have five of each of Fridays, Saturdays and Sundays.
Never.
Every year has more than 5 Fridays, 5 Saturdays and 5 Sundays.
This happens in any 31-day month starting on Friday (such as July 2005).
once every 365 years!
The month of July has 5 Saturdays and 5 Sundays zerotimes in 2012.
According to my desktop calendar, July will have five Fridays and Saturdays (and even some Thursdays) in 2016, 2021, 2022, 2027,2032, 2033, etc... If you look at http://www.timeanddate.com/calendar/monthly.html?year=2021&month=7&country=1 you will see that 2021, 2027, 2032 do not have 5 Sundays. The other years 2016, 2022, 2033 do have 5 Fridays, Saturdays, and Sundays. You are little confused since your first parahraph discusses Fridays and Saturdays, in which case 2021 and 2022 do indead have 5 Fridays and 5 Saturdays in July. In paragraph two above, you begin talking about Sundays and which years in which July will 5 each of Fridays, Saturdays and Sundays. Every month with 31 days will have 5 instances of the first 3 days in the month. This will repeat in a 5-6-5-11 year cycle and then repeat. So it should be 2016, 2022, 2033, 2039, 2044, 2050, 2056 - don't forget to consider leap year which will cause a 1 day shift.
Every time February 1st falls on a Monday !