Superstition and even numbers: why February only has 28 days

February is the only one of our twelve months that has 28 days.

Why actually?

There are solid astronomical reasons for this, but the decisive factor is human superstition from 2700 years ago.

February is 28 days long in normal years, including 2023, and 29 days in leap years.

This special feature has been its own since its invention.

We have to thank the ancient Romans: their year originally began in March (“mensis Martius”, or “month of Mars”) and lasted ten months (the name December comes from the Latin word “decem” – ten).

It was probably the Roman king Numa Pompilius who, around 700 BC, introduced two more months with Ianuarius and Februaryius in order to bring the Roman year better into line with the phases of the moon.

Like all calendar makers, Numa Pompilius had to struggle with the problem that nature doesn't do well with round numbers: they fit into a tropical year - the period in which the seasons repeat once, which is why it is the basis for our solar calendar not 365, but 365.242 days.

For a lunation - i.e. from one new moon to the next, the basis for our month - the moon does not need 30, but on average only 29.53 days.

Any calendar attempting the impossible task of cramming an integer number of days and months into a year must use regular "leap days" to compensate for the rounding errors that occur.

Even numbers were considered harbingers of bad luck

We don't want to take into account the fact that the length of days, months and years also change over time due to astronomical phenomena such as the elliptical shape of the earth's orbit or the inclination of the earth's axis!

Numa Pompilius assigned the role of the balancing month to the last month of his year - and thus to the Februaryius.

January and February were originally the last months of the year, appended to December.

At least as important to the king as astronomy was the aversion of his contemporaries to even numbers: these were considered harbingers of bad luck.

In order for the entire year to have an odd number of days, a month had to be even.

This is due to a simple mathematical fact: the sum of an even number of odd terms (twelve months in this case) is always even.

The Roman year was supposed to be 355 days long, so Numa Pompilius shortened February to 28 days so that all other 29-day or 31-day months could be odd.

February could live with the "unlucky" 28

February, that was probably the idea, could live with the "unfortunate" 28, since it was the month of Februa, the annual purification ritual.

And so it has remained to this day.

It is true that the Februa ritual has long been forgotten, and at some point January and February moved to the beginning of the year.

Julius Caesar's calendar reform also increased the year to the number of 365 days we are familiar with today – 366 in a leap year – but left February in its role as an outsider.

He remained the shortest month, and the one whose length changes in leap years.

The month may be short, but its nights are long: in mid-February, the night still lasts around 14 hours.

Enough time for a look at the starry sky, especially since the sun sets before 6 p.m.

Still at dusk, looking west, we can see two bright, whitish "evening stars" - the planets Venus and Jupiter.

Venus sets around 8 p.m., Jupiter about an hour later;

they can therefore no longer be found on our map, which was calculated for 10 p.m.

Mars holds the fort longer: We find it in the evening sky as a reddish glowing point between the constellations Carter and Taurus, roughly on the connecting line between the whitish Kapella and the orange-reddish Aldebaran.

Those with dark skies may also be able to see the faint band of the winter Milky Way.

It runs through the constellations Cassiopeia, Perseus, Carter, Gemini down to the Big Dog.

Numerous star clusters can be spotted with binoculars: the two brightest, the Pleiades and Hyades in Taurus, can also be seen on the map.

The Pleiades, also known as the Seven Stars, are a narrow group of stars between Perseus and Taurus, the Hyades are grouped around bright Aldebaran - which, however, does not physically belong to the star cluster.

Also in Perseus and between Perseus and Cassiopeia we find asterisms whose members belong together.

The next full moon is on February 5th

These star clusters are the remnants of former star-forming regions—regions of dense gas clouds from which new stars form.

An active star-forming region is the Great Orion Nebula in the constellation Orion: It can be found, again best with binoculars, in the southern part of the constellation, which is spanned by Rigel, the easterly shining star Saiph and the three "belt stars" in the center of the constellation.

While the winter constellations dominate the sky west of the meridian, we can already see the harbingers of spring in the east: the constellation Leo has fully risen and bright Arcturus is already flickering on the northeast horizon.

Which brings us to an astronomical reason for putting the shortest month of the year in winter (the northern hemisphere): because the earth is slightly closer to the sun on its orbit in January and February, it also moves according to Kepler's second law of planetary orbits more quickly.

Our winter half-year is actually a few days shorter than the summer half-year - without any superstition about numbers!

Sun:

February 1, sunrise 8:00 a.m., sunset 5:19 p.m.;

February 28, sunrise 7:12 a.m., sunset 6:05 p.m.

Moon:

February 5, 7:29 p.m.: full moon;

February 13, 5:01 p.m., Last Quarter;

February 20, 8:06 am, new moon;

February 27, 9:06 am, First Quarter.