Germanic calendar inspired by the Julian calendar, introduced a purely solar reckoning with a year having a fixed number of weeks (52 weeks or 364 days). This necessitated the introduction of "leap weeks" instead of Julian leap days. The old Icelandic calendar is not in official use any more, but some Icelandic holidays and annual feasts are still calculated from it. It has 12 months, of 30 days broken down into two groups of six often termed "winter months" and "summer months". The calendar is peculiar in that each month always start on the same day of week. This was achieved by
Leap year 25) fell on a Sunday in 2016, and Monday in 2017, then it will fall on Tuesday in 2018, and Wednesday in 2019 but then "leaps" over Thursday to fall on a Friday in 2020. The length of a day is also occasionally changed by the insertion of leap seconds into Coordinated Universal Time (UTC), owing to the variability of Earth's rotational period. Unlike leap days, leap seconds are not introduced on a regular schedule, since the variability in the length of the day is not entirely predictable. In the Gregorian calendar, the standard calendar in most of the world,