If someone gives me any date between 1752 when the Gregorian calendar made its 12-day adjustment and 2100 I can tell him or her what day of the week that date fell on. The Gregorian calendar made its 12-day adjustment in September 1752. It adopted from the old, slower, Julian calendar. The date was 1st September 1752 and then it suddenly jumped to 14th September 1752 the next day instead of the 2nd, so we lost 12 days that year.
Before 1752 Christmas Day was held on January 6th. Afterwards it was held on December 25th. In Britain you usually get your worst snowfalls in January and February in winter, after Christmas. This is probably where the idea of the White Christmas comes from. Before 1752, the new year started on 25th March. After 1752, it started on the 1st January.
Anyway.... I will pick some dates out at random....
What day of the week was 3rd February 1980? This was a Sunday.
What day of the week was 27th April 1914? Monday.
What day of the week was 6th June 1893? Tuesday.
What day of the week was 29th August 1945? Wednesday.
What day of the week was 23rd September 1779? Thursday.
What day of the week was 13th May 1842? Friday
What day of the week was 8th July 1826? Saturday.
The penchant for dates also extends to birthdays. Today it still remains. I could remember everyone's birthdays in the entire school I attended. I was unpopular of course because when I didn't buy anyone a birthday card they said I had no excuse. I can also remember most famous people's birthdays.
I also notice another few things with calendar calculating, unconsciously. Say if someone was born in 1939 and someone was born in 1970. In 2010, a person who was born in 1970 was 40 years old and a person who was 701 years old was born in 1940. In the instance of someone born in 1940, they were 70 in the year 2010, as someone born in the year ending in 40 will be the same age in 2010 as the last two digits of the year given in that first example - merely a case of '70 + 40' and '40 + 70' being equal to 110
I've noticed that for some years in the 20th century that the calendar is the same exactly 45 years later. Turn the numbers around for 1905 and you get 1950. Do the same for 1916 and you get 1961. For example, the calendars of 1905 and 1950 were exactly the same, as were those of 1938 and 1983, as well as 1949 and 1994. 1916 was exactly the same as 1961 from the 1st March 1916 onwards. The calendars of 1927 and 1972 were the same up to the 28th February, then they diverged, as 1972 was leap year. Also the calendars of 1972 and 1977 were the same up to the 28th February 1977. 12th February 1972 was a Saturday, and five years later, 12th February 1977 was also a Saturday.
The calendar dates for two years 45 years apart are identical, which is easily explained by the fact that 7 (the number of days in a week) is a factor of the sum of 45 and the number of leap years covered within a 45-year period (sum difference only), i.e. 11. Therefore, 45 + 11 = 56 / 7 = 8.
You get a reverse with a difference of 36 years with 1904 and 1940, 1915 and 1951, 1926 and 1962, 1937 and 1973, 1948 and 1984 and 1959 and 1995. An increase of 11 years with each value.
If someone was born in 1941, they were 9 years old in 1950. However, if you turn their birth year around to 1914, and reverse 1950 to 1905, then you find that the person born in 1905 was 9 years old in 1914.
Also another pattern occurs with the number 9 if you reverse certain years around. If you reverse 1901 and 1910 around you get 9. If you reverse 1902 and 1920 around you get 18. Between 1903 and 1930 it is 27. Between 1904 and 1940 it is 36. Between 1905 and 1950 it is 45. Between 1906 and 1960 it is 54. Between 1907 and 1970 it is 63. Between 1908 and 1980 it is 72 and between 1909 and 1990 it is 81.
If you take 5 from 50, 16 from 61, 38 from 83 and 49 from 94 you get 45 each time. The number 45 is divisible by 5 and that comes to 9. Also, 4 plus 5 comes to 9. I was not a mathematical expert then and am not now, but I found this very interesting.
The 21st August 1805 fell a Wednesday, then fell on a Wednesday 45 years later on 21st August 1850, then again in 1895, 1940, 1985, 2030, 2075, 2120 and 2165. It finally ends in 2210, which for some falls on a Tuesday. However, this 45-year rule, where it happens in a run of values like those stated above, only happens with certain years. Interestingly, they seem to happen with leap years. 25th April fell on a Sunday in 1909, 1954 and 1999 but then in 2044 on a Monday. It also fell on a Monday in 1864.
