The Gregorian Calendar is used in most parts of the world today. In order to keep this calendar in synch with the solar year (the time for the Earth to complete one orbit around the sun), it has leap years with an extra day in February. Leap years generally occur every four years, in years that are divisible by \(4\). However, years divisible by \(100\) are excluded, UNLESS they are divisible by \(400\). For example, the year \(2000\) was a leap year, but \(1900\) was not.
The year \(2025\) has a different calendar than the year \(2024\) since it started on a different day of the week. January \(1\), \(2024\) was on a Monday, while January \(1\), \(2025\) was on a Wednesday.
January \(1\), \(2023\) was on a Sunday. Explain why January \(1\), \(2024\) was one day of the week later than in \(2023\), while January \(1\), \(2025\) was two days of the week later than in \(2024\).
January \(1\), \(1992\) and January \(1\), \(2025\) were both on a Wednesday. Did \(1992\) have the same yearly calendar as \(2025\)?
How many different yearly calendars are there in total? Two yearly calendars are considered the same if each date occurred on the same day of the week.
Theme: Geometry & Measurement