Why is Tuesday of 2011 different day in 2012?

Answer 1

There are seven days of the week, but the number of days in the year is never evenly divisible by seven. Normal years have 52 weeks plus one day, and leap years have 52 weeks plus two days. Therefore, a certain date will usually be on the next day of the week the next year, except when there's a leap year day in between, then it skips a day. For example, February 12 was a Friday in 2010, Saturday in 2011, and Sunday in 2012. Since there is a leap year day between February 12, 2012 and February 12, 2013, February 12 will fall on a Tuesday in 2013.