The solar cycle is a period of time in the calendar system during which each of the seven days of the week has a leap year day. This means that during a solar cycle, every possible combination of days and dates occurs at least once. The solar cycle is 400 years in the Gregorian calendar system, which is used in most of the world.
The solar cycle was much shorter until the 16th century. Previously, most countries followed the Julian calendar, which was named after Julius Caesar. This followed the simple rule of 365 days per year, with a leap year on February 29th every fourth year. Because of how the Julian calendar works, if February 29th falls on a Monday in a given year, it will be 28 years before it does so again. This time period is known as the solar cycle.
The Gregorian calendar was adopted by a number of European countries in 1582. Over the next 350 years, other countries adopted the system, and it is now the standard in most of the world. The Gregorian calendar differs slightly from the Julian calendar in that a “year” in the Julian calendar is slightly longer than the time it takes the Earth to orbit the Sun.
To help correct this, the Gregorian calendar does not count leap years that end in 00 unless they can be divided by four. This means that while the years 1800, 1900, 2100, and 2200 are not leap years, the year 2000 is. Although a year on the Gregorian calendar is slightly longer than it is in reality, the difference is only 27 seconds per year, compared to 11 minutes on the Julian calendar.
Because of these differences, the Gregorian calendar’s solar cycle is much longer, taking 400 years to use every possible set of dates and days. In the lifetimes of most people alive today, however, this will never be an issue. Between 1901 and 2099, there are only 28 different sets of days and dates because there are no years that are exceptions to the usual leap year rules. This makes life a whole lot easier for companies that print calendars!
It’s important to note that the term “solar cycle” is sometimes used to refer to the time it takes the Earth to complete one orbit around the Sun. As previously stated, this time frame is slightly shorter than a calendar year. When referring to a calendar-related solar cycle, it may be safer to use the name of the calendar system to avoid confusion between the two uses of the term.