What is a Leap Year?

Klaus Botta, 13.02.2024

Leap year, leap day, the astrophysical background, the rules and exceptions - what does a leap year entail for us?

All these questions will be explained for you in this compact article.

Here you will find useful general knowledge summarized - simple and comprehensible in just 5 minutes.

A leap year is a year that has one day more than "normal years": 366 days instead of 365.

A leap day is precisely this day that is added every four years.

So far so clear.

Leap years are those years which can be divided by the number "four". For example, the years 2000, 2004, ... 2024, 2028 and so on.

But how come every fourth year has one more day and why the number four?

In this case, it's down to astrophysics once again. Specifically, the ratio of the Earth's rotations around its own axis to the duration of a complete orbit around the sun.

This sounds complicated but is actually relatively easy to explain.

What is a day, what is a year?

As a reminder: We call one revolution of the planet Earth around its own axis a day. It lasts 24 hours = 1 Earth day.

(Note: A stellar day is slightly shorter at 23 hours, 56 minutes and 4 seconds. For the sake of simplicity, in this article we always refer to the perceived earth day with exactly 24 hours).

We describe one complete orbit of the earth around the sun (covering a considerable 940 million kilometers) as a year.

The decisive point for the topic of "leap years" is as follows: during a year (= one complete orbit around the sun), the earth does not rotate exactly 365 times around its own axis (= 365 days) but instead about 365 ¼ times.

If a year were always defined as 365 days, the Earth would not make a full 360-degree orbit around the sun within a year, but only (365 : 365.25) x 360 degrees = 359.75 degrees. We would therefore lose about 0.25 degrees of orbit every year.

This is not particularly noticeable within a year. After 100 years, however, we would already have lost 25 degrees of orbit. Over the course of 1,000 years, we would have lost a staggering 250 degrees, or more than half a year!

This is unacceptable because it would completely shift our seasons (see also our article on the equinox)

The leap year in the Julian calendar and the Gregorian calendar

For this reason, an additional leap day was introduced by Julius Caesar in 45 BC. The month of February was chosen because in the Julian calendar the calendar year ended after February.

Even the measure of inserting the four-yearly leap day, still does not perfectly reflect the Earth's solar cycle, which is why the Gregorian calendar was introduced by Pope Gregory during the so-called calendar reform in 1582 AD, in which three regular leap days were dropped within 400 years.

This affects the so-called secular years, for example the years 1800, 1900, 2100, 2200 etc.

As you can see, this rule meant that the year 2000 was omitted. 2000 was therefore a completely normal leap year that follows the four-year rhythm.

The year 2024 is also a regular leap year with an additional leap day, February 29.

From a calendar perspective, time stands still for one day on February 29th

Seen in this way, February 29 is a gift day.

This prompted me to think about what this means in concrete terms for us 21st century people.

From a pragmatic point of view, February 29, 2024 will be a completely "normal day" like any other.

In this case, a Thursday, so also a normal working day.

From a meta-perspective, it is actually a real "gift day".

For this special day, for example, we pay no additional rent, no additional interest, we don't get a day older (numerically speaking). Figuratively speaking, time seems to stand still for a day.

Think about this phenomenon for a second. Above all because it also helps us to deal with the phenomenon of "time" more consciously. If you can think of anything interesting, please let us know in the comments. We look forward to hearing your thoughts and learning more.

Last but not least, the leap year with its leap day fits our brand philosophy "Watches for the conscious use of time" rather well.

Celebrate February 29 with us as a special day

With this in mind, I wish you a good (leap) year.

Come and join us in our office on February 29 to reflect on the topic of "time". Just drop by our office in Königstein. We will be happy to make time for you.

After all, a leap day is a free day for all of us ;)


  • Stefan Meinel

    Toll verständliche und sehr informative Erklärung zu dem, alle 4 Jahre, geschenkten Tag 👌👍 mit sogar noch viel mehr Informationen und Hintergrundwissen zu diesem Phänomen.
    Es wird schon einen Grund haben 😉 dass ich gerade heute meinen freien Tag habe 😁🙃😊
    In diesem Sinne einen entschleunigenden Tag am geschenkten Tag des Jahres, was man mit BOTTA Uhren generell auch schon kann 😊🍀🕡

  • Jürgen Herlt

    Ein sehr gut zusammengefasster und dabei gut verständlicher Artikel zum Schaltjahr mit interessanten Informationen drum herum. Einiges habe ich natürlich schon gewusst, aber einiges war mir auch vollkommen neu. ZB. dass auch die Kalenderreformen direkt mit dem Schaltjahr zusammenhängen, oder die Säkulartage waren mit bis dato unbekannt. Dank Ihres Artikels kann ich jetzt wieder mit meinem neuen Wissen angeben! ; ) Vielen Dank ich habe viel gelernt.

  • Jens Kretschmann

    Vielen Dank für die gute Erklärung.
    Einen schönen Sonntag wünsche ich Ihnen noch.

    Beste Grüße aus dem Allgäu

    Jens Kretschmann

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