Common things you know about but do not know why. Heres a list:

Why Are There Only 28 Days in February?

Thirty days hath September,

April, June, and November.

All the rest have 31,

Except for February,

Which got the short stick because it's cold and no one likes it.

Well, something to that effect. Some believe February once boasted 29 days and that Augustus Caesar stole a day so he could add it to August, which was named for him. (If there’s a month named after you, why not milk it?) But that’s a myth. Rather, February has 28 days because, to the Romans, the month was an afterthought. In the 8th century BCE, they used the Calendar of Romulus, a 10-month calendar that kicked the year off in March (with the spring equinox) and ended in December. January and February didn’t even exist:

Martius: 31 days

Aprilius: 30 days

Maius: 31 days
Junius: 30 days
Quintilis: 31 days
Sextilis: 30 days
September: 30 days
October: 31 days
November: 30 days
December: 30 days

Tally up those numbers, and you’ll see a problem—the year is only 304 days long. Back then, winter was a nameless, monthless period that no one cared for much. (Planters and harvesters used the calendar as a timetable. To them, winter was useless and wasn’t worth counting.) So for 61 days out of the year, Romans could ask “What month is it?” and you could correctly answer, “None!”

King Numa Pompilius thought that was stupid. Why have a calendar if you’re going to neglect one-sixth of the year? So in 713 BCE, he lined the calendar up with the year’s 12 lunar cycles—a span of about 355 days—and introduced January and February. The months were added to the end of the calendar, making February the last month of the year.

But no Roman calendar would be complete without some good old-fashioned superstition mixed in! The Romans believed even numbers were unlucky, so Numa tried to make each month odd. But to reach the quota of 355, one month had to be even. February ended up pulling the short stick, probably because it was simply the last month on the list. (Or as Cecil Adams puts it, “If there had to be an unlucky month, better make it a short one.”) Numa’s calendar ended up looking like this:

Martius: 31 days

Aprilius: 29 days

Maius: 31 days
Iunius: 29 days
Quintilis: 31 days
Sextilis: 29 days
September: 29 days
October: 31 days
November: 29 days
December: 29 days
Ianuarius: 29 days
Februarius: 28 days

Of course, a 355-day calendar had its bugs. After a few years went by, the seasons and months would fall out of sync. So to keep things straight, the Romans would occasionally insert a 27-day leap month called Mercedonius. The Romans would erase the last couple days of February and start the leap month on February 24—further evidence no one ever cared much for the month.

This caused headaches everywhere. The leap month was inconsistent, mainly because Rome’s high priests determined when it would arrive. Not only did they insert Mercedonius haphazardly, but the priests (being politicians) abused the power, using it to extend the terms of friends and trim the terms of enemies. By Julius Caesar’s time, the Roman people had no clue what day it was.

So Caesar nixed the leap month and reformed the calendar again. (To get Rome back on track, the year 46 BCE had to be 445 days long!) Caesar aligned the calendar with the sun and added a few days so that everything added up to 365. February, which by now was at the top of the calendar, kept its 28 days. We can only imagine it’s because Caesar, like everyone before and after him, just wanted it to be March already.

Why Don’t British Royals Use a Last Name?

Among the many upsides to being British royalty, there is this: You never have to use a last name. For one thing, everyone already knows who you are. There’s only one Queen, for instance, so it’s not like Elizabeth has to specify which one she is.

However, the British royal family does have a last name, as Business Insider reminds us. The British royal family’s last name is technically Windsor, but that’s a relatively new development.

Before 1917, royals were usually known by the territory they ruled or the Royal House of which they were a member, as the Royal Family’s website explains. For example: The full name of Queen Victoria’s eldest son, King Edward VII, was Albert Edward Saxe-Coburg-Gotha—a mouthful he inherited from his father, Prince Albert of Saxe-Coburg and Gotha.

In 1917, though, Edward’s son, George V, was presented with a conundrum: His surname sounded somewhat German, which was an unwelcome association during World War I, so he named his family after Windsor Castle. Since then, any descendants of Queen Victoria (aside from married women) bear the last name Windsor.

In 1960, to make things more confusing, Queen Elizabeth II and her husband, Prince Philip, decided to add their own spin to the Windsor name, distinguishing their descendants from the rest of the royal family. So her children and their children can use Mountbatten-Windsor as their surname on official documents such as marriage and birth certificates. (Fans of Netflix's The Crown caught a glimpse of the discussions that went into the surname decision, though the series didn't tell the full story.)

Kings and queens are welcome to change the last names of their family at will, since it’s a matter of precedent rather than an official decree. And royals sometimes adopt other names when it’s convenient. Princes Harry and William used Wales as their last name while serving in the military, adopting their father’s designation as the Prince of Wales.

With such a complicated naming protocol, it’s no wonder most Royal Family members go by their titles instead.

Why Are Wedding Rings Worn on the Left Hand?

For years, couples have dedicated a single "ring" finger to romance when any other digit would do. A case of left side, strong side? Not according to history.

In medieval times, getting caught scribbling with one's left hand could earn accusations of being possessed and, during the Spanish Inquisition, lefties were more likely to be tortured or killed. In fact, the aversion touched many cultures, from the long-standing taboo in Islamic countries against eating and drinking with one’s left hand, to the expectation in ancient Japan that any wife who didn’t favor her right could be legally divorced on the spot, no questions asked. So why do we favor a finger on a cursed hand to symbolize lasting love?

Past perception wasn't all bad. The union between marriage and the now-standard ring placement can be traced back to second-century Egyptians who falsely believed that “a certain most delicate nerve” began in the fourth left finger and stretched directly to the heart, according to the Greek scholar Appian. Centuries later, the Romans came to a similar conclusion. In place of a nerve, they were convinced that a vena amoris—or “lover’s vein”—connected this digit with the blood-pumping organ.

During the Roman engagement process, a well-off suitor who could afford a ring would slip it over his bride-to-be’s fourth finger. Thus, he’d always have a symbolic grip around her lover’s vein. The modern world may have adopted that practice from the Romans.

Still, others argue that reverence for the fourth finger begun as an early Christian ritual. While crossing themselves in an Orthodox Church, worshipers are expected to join the thumb with the index and middle fingers. Historians contend that the group represented the father, son, and Holy Ghost when placed together, while the “ring” finger signified earthly love, making it the perfect location for a spouse’s wedding ring.

Until the seventeenth century, Orthodox couples normally wore their rings on the right hand (an extremity that’s associated with strength) and most Europeans of all faiths followed suit. But during the Reformation in 1549, an English Bishop and Protestant reformer named Thomas Cranmer used wedding rings as a way to break from tradition. That year, he published The Book of Common Prayer, which instructs couples to ditch a centuries-old practice in favor of slipping their wedding rings over the left fourth finger. Before long, husbands and wives throughout the continent were doing so.

Why Don't Airlines Have Parachutes for Passengers?

There are four reasons why you don't find a parachute under your seat on commercial airlines:

1. Parachutes are bulky, heavy and expensive. They would not even fit under your seat, they would occupy a lot of space, and add a lot of weight. They would also need regular inspection and repacking. To provide several hundred per airplane would add significantly to costs, making flying much more expensive.

2. Passengers are not trained to use them. Without a minimum of training most people would not even be able to strap the parachute on correctly, never mind open it and land safely. Even on the ground and with plenty of time this is not easy. In the confined space of an airliner and in a high-stress situation it would be even more difficult.

3. There isn't a convenient way to jump out of typical airliners. You would need to redesign aircraft with a special jumping exit. Just jumping out of normal side-facing airplane doors or emergency hatches you would probably hit the wing or the tail. You would need to install a ramp on the rear of the cabin.

4. There are very few situations where it would save anybody. You would have to be in a situation, in daylight, over land, where there is no hope of a landing but plenty of time to get everyone out. I can only think of a single case in the entire history of civil aviation where it could have been useful—The United Airlines Flight 232 case—but then only if the aircraft had been redesigned with a rear exit. Even in that case, jumping was as risky as staying aboard.

Why Are Movie Previews Called 'Trailers'?

There is no part of a film's marketing that's more important than its trailer. An entire film's financial success—and a studio's very future—can be determined by a mere two-and-a-half minute preview released months in advance of a movie's premiere. Case in point: More than 13 million people watched Warner Bros.' first Wonder Woman trailer on YouTube within 48 hours of its release—giving the movie the type of buzz that executives can only dream of. Even if the movie isn't well received by critics, the good will from a successful trailer can still carry it toward a healthy profit.

But amid all the hype attached to trailers, there's one big question that we don't really think about: Why are these previews even called trailers when they're shown before films?   Well that's just the thing, they weren't always played before movies—and the very first trailer on record wasn't even for a film. It was actually for a 1913 play called The Pleasure Seekers.

As pointed out in the above video by FilmmakerIQ, the moviegoing experience was much different in 1913. You would pay your admission—usually just a couple of cents—and you could basically sit inside a movie house all day and watch whatever was playing, often a combination of feature-length movies, short films, and cartoons. To take advantage of the audience members sitting and waiting for the next movie to play, Broadway producer—and movie theater advertising manager—Nils Granlund came up with the profitable idea of advertising upcoming plays in between screening rotations at Marcus Loew's East Coast theater chain. By using rehearsal footage from The Pleasure Seekers, Granlund put together a short promotional film for the play, creating buzz and bolstering publicity for the production. He also, unknowingly, revolutionized film marketing.

In the spirit of cramming advertising into every nook and cranny of our lives, the idea quickly evolved. That same year, producer William Selig brought the popular serial format from the newspapers to the big screen—producing short action-adventure story installments that always ended with some type of thrilling cliffhanger that implored people to come back next week to find out if the hero escaped certain death. Well, how else do you get an audience back for more? Selig figured the best way to do this was to have a brief teaser for the following episode play after the main feature, so the audience would leave the theater wanting more. This was the first step toward a traditional movie trailer.

These initial trailers for Selig's first serial, The Adventures of Kathlyn, were usually nothing more than a brief bit of footage accompanied by text that screamed questions at the audience, like "Does she escape the lion's pit? See next week's thrilling chapter!" This idea worked so well that studios were soon cutting their own trailers, as opposed to the individual theaters doing it for them. After that, trailer production was outsourced by studios to the National Screen Service, which held onto a trailer monopoly for more than four decades.

Trailers soon became big business, eventually moving to the familiar position we know today, before a movie begins. This ensures more eyes on the product, and probably made more sense once the serial storytelling model was phased out. So while the term "trailer" might not make sense anymore—especially since these previews are mainly viewed on YouTube nowadays anyway—we're too set in our ways to change it now.

Why Don't Formula 1 Cars Have Airbags?

Because F1—and the drivers—have other safety mechanisms that are better suited than airbags to the task at hand. There's no chance in an F1 car that the driver is flung out unless the car itself has totally disintegrated; and even so, he's in the survival cell of the F1 car.

For starters, drivers wear helmets; but more than helmets, they wear what is called a HANS device (a head and neck support):

This sits on their shoulders and prevents potentially fatal Basilar skull fractures.

In addition, instead of your three-point seatbelt, they likely have a five-point harness:

All of these mean that there's no chance the driver's head will hit the front of the car (the primary purpose of airbags). Furthermore, the driver sits in a survival cell that is designed to be rigid in the event of a crash:

The survival cell is the part in yellow.

Why Are Airplane Windows Round?

While some passengers might be too terrified—or sedated—to notice, frequent travelers may sometimes wonder why the windows that line airplane rows are round. Windows in the home are rectangular; car partitions are angled, but mostly rectangular. Why don’t planes follow suit?

It’s actually not an aesthetic choice. Airplanes used to have square windows. And they wound up crashing because of them.

When commercial airlines graduated to faster and larger jets beginning in the 1950s, planes would sometimes essentially disintegrate midair. Two of them, both de Havilland Comets, fell apart within months of one another in 1954 and killed a total of 56 passengers. Investigators traced the flaw to the squared-off corners of windows, which collect the stress of a pressurized cabin and can be prone to fracture. During one test, the Royal Aircraft Establishment found that up to 70 percent of the airplane’s stress was concentrated on the window's sharp angles.

Circular windows, which are able to disperse that pressure more evenly, immediately became the new standard in passenger aviation. And for every one you see, there are actually three panes at work: one bears the burden of pressurization, another inner pane acts as a failsafe in case the outer pane fails—which is rare—and one “scratcher” pane faces the occupant, so that you can smudge and dirty it up to your heart’s content.

As for that little hole at the bottom: It’s there to make sure the working pane takes the brunt of the air pressure, maintaining the emergency pane for, well, emergencies.

Mystery solved.

Culled