Why Do Passports Only Come in Four Colors?

iStock
iStock

Passports are only made in shades of blue, red, green, and black.

You might assume that this is because of regulations governing which colors passports can be, but there's actually no official rule dictating acceptable passport color. In fact, there are no rules about what passports should look like at all, only suggestions. The International Civil Aviation Organization (ICAO) makes recommendations about typeface, type size, and font in their guide for machine readable travel documents (MRTDs), a category which includes passports.

There are some hard and fast regulations in this document, however: Passports must be made of a material that bends (no creasing) and remain machine readable at temperatures ranging from 14 to 122°F and at relative air humidity ranging from five to 95 percent.

Although passports only come in these four colors, there's a lot of variation when it comes to the actual shade. Many countries opt for darker shades of blue, red, and green. The reason for the limited color choice is pretty much what you'd think: Countries choose these simple, dark hues because they look official. Millennial pink wouldn't look very bureaucratic. Dark colors are also less likely to show dirt and wear. (You can browse the world's passports with this nifty website.)

Anthony Philbin, ICAO’s chief communications officer, confirmed to Travel + Leisure that when it comes to passports, “Nothing stipulates the cover color.” Basically, there's nothing stopping the United States from making its passports lime green except a sense of propriety. William Waldron, the vice president of security products at Holliston, LLC (which makes passports for more than 60 countries) told Travel + Leisure that they can manufacture “any color that’s in the Pantone book.”

There's often meaning behind which of the four colors a country chooses. For example, most Islamic states use green passports because the color is significant in their religion. Though the majority of passports issued in the U.S. today are blue, that change came about in 1976, as part of the bicentennial celebration; prior to that, from 1941 to 1976, American passports were green—a color that made a triumphant return between 1993 and 1994 and included a special tribute to Benjamin Franklin.

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Why Are Sloths So Slow?

Sloths have little problem holding still for nature photographers.
Sloths have little problem holding still for nature photographers.
Geoview/iStock via Getty Images

When it comes to physical activity, few animals have as maligned a reputation as the sloth. The six sloth species, which call Brazil and Panama home, move with no urgency, having seemingly adapted to an existence that allows for a life lived in slow motion. But what makes sloths so sedate? And what horrible, poop-related price must they pay in order to maintain life in the slow lane?

According to HowStuffWorks, the sloth’s limited movements are primarily the result of their diet. Residing mainly in the canopy vines of Central and South American forests, sloths dine out on leaves, fruits, and buds. With virtually no fat or protein, sloths conserve energy by taking a leisurely approach to life. On average, a sloth will climb or travel roughly 125 feet per day. On land, it takes them roughly one minute to move just one foot.

A sloth’s digestive system matches their locomotion. After munching leaves using their lips—they have no incisors—it can take up to a month for their meals to be fully digested. And a sloth's metabolic rate is 40 to 45 percent slower than most mammals' to help compensate for their low caloric intake. With so little fuel to burn, a sloth makes the most of it.

Deliberate movement shouldn’t be confused for weakness, however. Sloths can hang from branches for hours, showing off some impressive stamina. And because they spend most of their time high up in trees, they have no need for rapid movement to evade predators.

There is, however, one major downside to the sloth's leisurely lifestyle. Owing to their meager diet, they typically only have to poop once per week. Like going in a public bathroom, this can be a stressful event, as it means going to the ground and risking detection by predators—which puts their lives on the line. Worse, that slow bowel motility means they’re trying to push out nearly one-third of their body weight in feces at a time. It's something to consider the next time you feel envious of their chill lifestyle.

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Are Any of the Scientific Instruments Left on the Moon By the Apollo Astronauts Still Functional?

Apollo 11 astronaut Neil Armstrong left the first footprint on the Moon on July 20, 1969.
Apollo 11 astronaut Neil Armstrong left the first footprint on the Moon on July 20, 1969.
Heritage Space/Heritage Images/Getty Images

C Stuart Hardwick:

The retroreflectors left as part of the Apollo Lunar Ranging Experiment are still fully functional, though their reflective efficiency has diminished over the years.

This deterioration is actually now delivering valuable data. The deterioration has multiple causes including micrometeorite impacts and dust deposition on the reflector surface, and chemical degradation of the mirror surface on the underside—among other things.

As technology has advanced, ground station sensitivity has been repeatedly upgraded faster than the reflectors have deteriorated. As a result, measurements have gotten better, not worse, and measurements of the degradation itself have, among other things, lent support to the idea that static electric charge gives the moon an ephemeral periodic near-surface pseudo-atmosphere of electrically levitating dust.

No other Apollo experiments on the moon remain functional. All the missions except the first included experiment packages powered by radiothermoelectric generators (RTGs), which operated until they were ordered to shut down on September 30, 1977. This was done to save money, but also because by then the RTGs could no longer power the transmitters or any instruments, and the control room used to maintain contact was needed for other purposes.

Because of fears that some problem might force Apollo 11 to abort back to orbit soon after landing, Apollo 11 deployed a simplified experiment package including a solar-powered seismometer which failed after 21 days.

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

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