And if you really want to blow some minds get students to figure out
the difference between the Julian and modern or Gregorian calendar.
Hint: The Gregorian calendar omits the century leap days except when
the year is evenly divisible by 400. Fortunately we had a normal leap
day in 2000, because I doubt that most of the computer clocks take
into account the Gregorian calendar difference. Many of them will
wrap around in the near future due to the inadequate word length used.
I forget the date and I am too lazy to look it up. Incidentally when
I wrote a program to graph dates I put in the correct century leap
days.
BTW some countries such as Greece did not change their calendar until
the 20th century as I recall.
The Julian calendar is useful because some groups celebrate the Julian
New Year which gives one the opportunity for another party after the
Gregorian New Year. As a trivia question: What date is Julian New
Year in our calendar. You can find it on the web, but please no
peeking until you have figured it out.