As of: February 29, 2024 6:55 a.m
Every four years the calendar shows February 29th, like today. Why do we need such leap years and what exceptions are there?
Translating the regular sequence of day and night, summer and winter into a number system seems banal. But people have been trying to find the perfect solution for more than 2,000 years. Apparently everything fits: a year has 365 days and then spring, summer, autumn and winter begin again. But every four years – like this year – the calendar gets out of rhythm and the year consists of 366 days. Only February 29th in such leap years ensures that the Gregorian calendar, which has been in use worldwide since the 16th century, also corresponds to the change of seasons in the long term.
Why 365 and when 366 days?
In our solar system, the Earth revolves constantly around the sun. It takes 365 days to complete a full circle around it. Strictly speaking, however – with some fluctuations in the orbital period – there is an average of 365.2422 days, i.e. around 5 hours and 49 minutes more than a calendar year. This period is called the tropical year or solar year. After this time, the earth’s orbit reaches the point where day and night are of equal length in spring, the vernal equinox.
After four years, the additional hours have added up to around 24, or one day. This is added to the calendar as February 29th of a leap year. Without the additional day, the calendar would deviate from the course of the seasons: for example, after 400 years, the longest day of the year would no longer be June 21st, but a day at the end of September.
Is every four years a leap year?
Leap years are all years with numbers that can be divided as an integer by four. Example: 2024:4=506. But there are exceptions. Since the Earth needs a little less than 365 and a quarter of a day to travel around the sun, February 29th is omitted every 100 years. This happens in years that can easily be divided by 100: around 1800, 1900, 2100.
The year 2000 was another exception. In order to adapt the calendar even more precisely to the tropical year, there is also February 29th in all years that are divisible by 400, such as 1600 and 2000. With this calculation, the deviation between Calendar year and tropical year only on one day in 3,000 years.
Further information
December 22nd is the shortest day of the year. In the north there is barely 7.5 hours of light. After that the days get longer again. more
At the end of October the clocks went back one hour. It gets light earlier in the morning and darker in the evening. more
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NDR Info | Current | 02/29/2024 | 07:37 am