How Does the Magic Yellow First-Down Line Work?

Sportvision
Sportvision

If you attend a Super Bowl party on Sunday, you’ll probably hear at least one casual football viewer ask, “How do they get that yellow first-down line on the field?” While “magic” is a fine answer in its own right, the real explanation is a bit more technologically intense. Let’s have a look at the background and mechanics behind every football fan’s shining beacon: the yellow first-down line.

According to Allen St. John’s 2009 book The Billion Dollar Game: Behind the Scenes of the Greatest Day in American Sport - Super Bowl Sunday, the first-down line actually emerged from the ashes of one of sports broadcasting’s bigger debacles: the FoxTrax system for hockey, which was designed by a company called Sportvision. FoxTrax—which hockey fans no doubt remember as the much-maligned “technopuck” that debuted in 1996—employed a system of cameras and sensors around a hockey rink to place a little blue halo around the puck.

FoxTrax wasn't a great fit for NHL broadcasts: Hockey purists hated the intrusion into their game, and casual fans didn’t flock to hockey just because the puck was suddenly easier to follow. However, the system inspired producers to think of new ways to insert computerized images into live sports broadcasts.

The idea of using a line to mark the first down in football was a natural extension, and Sportvision debuted its 1st and Ten system during ESPN’s broadcast of a Bengals-Ravens tilt on September 27, 1998. A couple of months later, rival company Princeton Video Image unveiled its Yellow Down Line system during a Steelers-Lions broadcast on CBS. (Sportvision is still kicking, and ESPN acquired all of PVI’s intellectual property in December 2010.)

BUT HOW DOES IT WORK?

It takes lots of computers, sensors, and smart technicians to make this little yellow line happen. Long before the game begins, technicians make a digital 3D model of the field, including all of the yard lines. While a football field may look flat to the naked eye, it’s actually subtly curved with a crown in the middle to help rainwater flow away. Each field has its own unique contours, so before the season begins, broadcasters need to get a 3D model of each stadium’s field.

These models of the field help sidestep the rest of the technological challenges inherent to putting a line on the field. On game day, each camera used in the broadcast contains sensors that record its location, tilt, pan, and zoom and transmit this data to the network’s graphics truck in the stadium’s parking lot. These readings allow the computers in the truck to process exactly where each camera is within the 3D model and the perspective of each camera. (According to How Stuff Works, the computers recalculate the perspective 30 times per second as the camera moves.)

After they get their hands on all of this information, the folks in the graphics truck know where to put the first-down line, but that’s only part of the task. When you watch a football game on television, you’ll notice that the first-down line appears to actually be painted on the field; if a player or official crosses the line, he doesn’t turn yellow. Instead, it looks like the player’s cleat is positioned on top of an actual painted line. This effect is fairly straightforward, but it’s difficult to achieve.

To integrate the line onto the field of play, the technicians and their computers put together two separate color palettes before each game. One palette contains the colors—usually greens and browns—that naturally occur on the field’s turf. These colors will automatically be converted into yellow when the line is drawn on to the field.

All of the other colors that could show up on the field—things like uniforms, shoes, footballs, and penalty flags—go into a separate palette. Colors that appear on this second palette are never converted into yellow when the first-down line is drawn. Thus, if a player’s foot is situated “on” the line, everything around his cleat will turn yellow, but the cleat itself will remain black. According to How Stuff Works, this drawing/colorizing process refreshes 60 times per second.

All this technology—and the people needed to run it—wasn’t cheap at first. It could cost broadcasters anywhere from $25,000 to $30,000 per game to put the yellow line on the field. Sportvision had to deploy a truck and a four-man crew with five racks of equipment. The cost has come down since then, and the process is now less labor-intensive. One technician using one or two computers can run the system, according to Sportvision, and some games can even be done without anyone actually at the venue.

Now you can explain it to everyone at your Super Bowl party during one of the less-exciting $5 million commercials.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

This post originally appeared in 2011.

Why Do Bats Hang Upside Down?

iStock.com/CraigRJD
iStock.com/CraigRJD

Stefan Pociask:

The age-old question of upside down bats. Yes, it is awfully weird that there is an animal—a mammal even—that hangs upside down. Sure, some monkeys do it when they're just monkeying around. And a few other tree climbers, like margays, hang upside down if they are reaching for something or—again, like the margay cat—may actually even hunt that way ... But bats are the only animals that actually spend most of their time hanging upside down: feeding this way, raising their young this way, and, yes, sleeping or roosting this way.

There is actually a very good and sensible reason why they do this: They have to hang upside down so that they can fly.

First off, we have to acknowledge that bats are not birds, nor are they insects. These are the other two animals that have true powered flight (as opposed to gliding). The difference between bat flight and bird or insect flight is weight—specifically, the ratio of weight to lift-capacity of the wings. If you walk up to a bird or insect, most species will be able to fly right up into the air from a motionless position, and do it quickly.

Bats, on the other hand (or, other wing), can’t do that. They have a lot of difficulty taking off from the ground (not that they can’t do it ... it’s just more difficult). Insects and birds often actually jump into the air to give them a start in the right direction, then their powerful wings take them up, up, and away.

Birds have hollow bones; bats don’t. Insects are made of lightweight chitin or soft, light tissue; bats aren’t. And bats don’t have what you could call "powerful" wings. These amazing creatures are mammals, after all. The only flying mammals. Nature found a way to evolve such an unlikely thing as a flying mammal, so some compromises had to be made. Bats, once airborne, manage perfectly well in the air, and can literally fly circles around most birds in flight. The problem is in first getting off the ground.

To compensate for the extra weight that mammals must have, to compensate for the problem of getting off the ground, evolution found another way for bats to transition from being motionless to immediately being able to fly when necessary. Evolution said, “How about if we drop them from above? That way they are immediately in the air, and all they need to do is start flapping."

It was a great idea, as it turns out. Except bat feet aren’t any good for perching on a branch. They are mammals, not birds, so their musculature, their bones, and their tendons are set up in a completely different way. When a bird squats down on a branch, their tendons actually lock their toes into an even tighter grip on the perch. It happens automatically. That’s part of being a bird, and is universal. That’s why they don’t fall off in their sleep.

Bats, as mammals, are set up differently. Therefore, to compensate for that fact, nature said, “How about if we have them hang upside down? That way, their tendons will actually pull their toes closed, just like a bird does from the opposite direction.” So that’s what evolved. Bats hang from the bottom of something, and all they have to do is "let go" and they are instantly flying. In fact, with this gravity-assist method, they can achieve instant flight even faster than birds, who have to work against gravity.

Side note: In case you were wondering how bats poop and pee while upside down ... First off, pooping is no big deal. Bat poop looks like tiny grains of rice; if they are hanging, it just falls to the floor of the bat cave as guano. Pee, however ... well, they have that covered too. They just “hold it” until they are flying.

So there you go. Bats sleep hanging upside down because they are mammals and can’t take off into the air like birds can (at least not without difficulty). But, if they're hanging, all they do is let go.

Makes total sense, right?

Now, having said all that about upside down bats, I must mention the following: Not all of the 1240-plus species of bats do hang upside down. There are exceptions—about six of them, within two different families. One is in South America (Thyropteridae) and the other is in Madagascar (Myzopodidae). The Myzopodidae, which includes just one species, is exceedingly rare.

So it turns out that these bats roost inside the tubes of young, unfurled banana leaves and other similar large leaves. When they attach themselves to the inside of this rolled leaf, they do it head-up. The problem with living inside of rolled-up leaves is that within a few days, these leaves will continue growing, and eventually open up. Whenever that happens, the whole group of bats has to pick up and move to another home. Over and over again. All six of these species of rare bats have a suction cup on each wrist and ankle, and they use these to attach to the smooth surface of the inside of the leaf tube. Evolution: the more you learn, the more amazing it becomes.

This post originally appeared on Quora. Click here to view.

What's the Difference Between Tequila and Mezcal?

iStock.com/mediaphotos
iStock.com/mediaphotos

Aside from tacos, enchiladas, and other tasty tortilla-wrapped treats, tequila and mezcal are among some of Mexico’s best-known offerings in the food and beverage category. These tipples, made from the agave plant, are so embedded in the country’s culture that Mexico City even has a museum dedicated to the two drinks, and Jose Cuervo operates a "tequila train" to none other than the city of Tequila. These beverages can be used to make a variety of cocktails, from the tequila sunrise to the mezcalita, but unless you’re a bartender or a connoisseur of spirits, you might not know the difference between the two. Is mezcal just fancier tequila?

Not exactly. Tequila is a type of mezcal, but the reverse isn’t always true. It’s similar to the distinction between champagne and sparkling wine, in which the name of the beverage depends on whether it was produced in the Champagne region of France or elsewhere. While mezcal can be produced anywhere in Mexico, tequila is made in the Mexican state of Jalisco (though a few exceptions do apply).

Tequila and mezcal also differ in the ingredients from which they are derived. Mezcal can come from any of the dozens of agave plants—a type of desert succulent—that are grown throughout Mexico. Tequila is made specifically from blue agave and, depending on the variety and brand, a bottle will contain between 51 percent and 100 percent of the plant-based nectar. According to The Tierra Group, a wholesaler of agave products, blue agave nectar is especially sweet because it’s 80 percent fructose, per Mexico’s regulations.

Lastly, tequila and mezcal taste different because of the ways in which they are prepared. Mezcal tends to have a savory, smoky, earthy flavor because the agave hearts (or piñas) are left cooking for several days in a fire pit that has been lined with volcanic rock and covered with agave leaves and earth. The piñas destined to end up in tequila, on the other hand, are often cooked in a brick oven, then crushed up to extract the juice.

If you ever feel adventurous at the liquor store and decide to bring home a bottle of mezcal, just keep in mind that there’s a particular way to drink it. “The first mistake many people make is pouring mezcal in a shot glass and pouring it down their throat,” Chris Reyes, a mixologist at New York City’s Temerario bar and restaurant told Liquor.com. Instead, the spirit is best sipped in a clay cup known as a jicarita.

Some words of advice if you do go shopping for mezcal: If you ever see a worm at the bottom of the bottle, that means it’s probably not a very good mezcal, according to Reyes. By contrast, tequila bottles should never have worms in them (despite the common misconception). So if you’re looking to avoid invertebrate-infused concoctions at all costs, tequila is your best bet.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

SECTIONS

arrow
LIVE SMARTER