Day of the week calculator

Many years ago, being still a schoolboy, the author of this site began to study programming for the web. He soon became convinced that he was a genius and invented a super original idea: to use Martin Gardner’s method to write a script that determines the day of the week for any date...
At the end of the school, the author became neither genius nor programmer, while the idea did not pass the originality test. On the other hand, sitting on the shore, the author saw some interesting new opportunities offered by the progress of programming languages. Now it is really easy
to calculate the day of the week for any date.

Which date are you interested in?