text: Examples The oldest solar calendars include the Julian calendar and the Coptic calendar.
  They both have a year of 365 days, which is extended to 366 once every four years, without exception, so have a mean year of 365.25 days.
  As solar calendars became more accurate, they evolved into two types.
  Tropical solar calendars
  If the position of the Earth in its orbit around the Sun is reckoned with respect to the Equinox, the point at which the orbit crosses the celestial equator, then its dates accurately indicate the seasons, that is, they are synchronized with the declination of the Sun. Such a calendar is called a tropical solar calendar .
  The duration of the mean calendar year of such a calendar approximates some form of the tropical year, usually either the mean tropical year or the vernal equinox year.
  The following are tropical solar calendars:
  Ancient Armenian calendar
  Gregorian calendar
  Bengali calendar (National and official calendar in Bangladesh)
  Iranian calendar (Jalāli calendar)
  Tabarian calendar (Tabarian calendar)
  Indian national calendar (Saka calendar)
  Every one of these calendars has a year of 365 days, which is occasionally extended by adding an extra day to form a leap year, a method called "intercalation", the inserted day being "intercalary".