Why Is It So Dark in Outer Space?

iStock/blackdovfx
iStock/blackdovfx

by Kenny Hemphill

Interstellar. Gravity. 2001: A Space Odyssey. Even Star Wars. They all have one thing in common: Beyond the lights of their spacecrafts, and aside from the faint needlepoint glow of distant stars, space is oil-slick dark.

Why that should be so is a question scientists have been asking for more than 400 years. Everyone from Johannes Kepler to Edmond Halley has had a go at trying to figure it out. But it was German astronomer Heinrich Wilhelm Olbers who gave his name to the paradox of the dark sky. Olbers wondered: If the universe is infinite, and there are an infinite number of infinitely old stars, why isn't the light from those stars visible from Earth? If it were, the night sky would be bright, not dark.

By the end of the 19th century, the idea of an infinite universe had been largely abandoned—something which was anticipated by Edgar Allan Poe in his 1848 essay, Eureka, where he wrote:

"Were the succession of stars endless, then the background of the sky would present us a uniform luminosity, like that displayed by the Galaxy—since there could be absolutely no point, in all that background, at which would not exist a star. The only mode, therefore, in which, under such a state of affairs, we could comprehend the voids which our telescopes find in innumerable directions, would be by supposing the distance of the invisible background so immense that no ray from it has yet been able to reach us at all."

In other words, Olbers' Paradox is resolved with the assumption that the universe has a finite age (something which is supported by the Big Bang Theory), that the speed of light is finite, and thus the observable universe has a horizon beyond which we can't see the stars. Fifty years later, Lord Kelvin used math to prove that in a finite universe, or one in which stars were born and died, the night sky should be dark.

There are other contributing factors to the darkness out there. Cosmic expansion over billions of years means that the energy from the radiation which was emitted following the Big Bang has been red-shifted, or reduced to the low temperature of microwaves. That puts it beyond the visible spectrum. And other radiation in space—infrared and ultra-violet light, radio waves, and X-rays—are all invisible to the human eye. If we could see them, space would seem a little less dark.

Universe Today has another explanation: "Space is black to our perception because there are few molecules of matter that can reflect or scatter light like our atmosphere on Earth. Since light goes in a straight line it seems to be absorbed by the void and vacuum of space. Otherwise space would look similar to the sky on Earth."

Think of a flashlight in a dark room. Look directly at the bulb and you see its light. Point it at furniture or a wall, and you see the light reflected. If there was nothing to reflect it, you wouldn't see any light at all. Which is exactly what happens in space.

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

Why Does Santa Claus Give Coal to Bad Kids?

iStock/bonchan
iStock/bonchan

The tradition of giving misbehaving children lumps of fossil fuel predates the Santa we know, and is also associated with St. Nicholas, Sinterklaas, and Italy’s La Befana. Though there doesn't seem to be one specific legend or history about any of these figures that gives a concrete reason for doling out coal specifically, the common thread between all of them seems to be convenience.

Santa and La Befana both get into people’s homes via the fireplace chimney and leave gifts in stockings hung from the mantel. Sinterklaas’s controversial assistant, Black Pete, also comes down the chimney and places gifts in shoes left out near the fireplace. St. Nick used to come in the window, and then switched to the chimney when they became common in Europe. Like Sinterklaas, his presents are traditionally slipped into shoes sitting by the fire.

So, let’s step into the speculation zone: All of these characters are tied to the fireplace. When filling the stockings or the shoes, the holiday gift givers sometimes run into a kid who doesn’t deserve a present. So to send a message and encourage better behavior next year, they leave something less desirable than the usual toys, money, or candy—and the fireplace would seem to make an easy and obvious source of non-presents. All the individual would need to do is reach down into the fireplace and grab a lump of coal. (While many people think of fireplaces burning wood logs, coal-fired ones were very common during the 19th and early 20th centuries, which is when the American Santa mythos was being established.)

That said, with the exception of Santa, none of these characters limits himself to coal when it comes to bad kids. They’ve also been said to leave bundles of twigs, bags of salt, garlic, and onions, which suggests that they’re less reluctant than Santa to haul their bad kid gifts around all night in addition to the good presents.

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

Why Are Poinsettias Associated with Christmas?

iStock
iStock

Certain Christmas traditions never seem to go out of style. Along with wreaths, gingerbread cookies, and reruns of A Christmas Story sits the poinsettia, a red-tinged leafy arrangement that’s become synonymous with the holiday. Upwards of 100 million of them are sold in the six weeks before December 25.

Why do people associate the potted plant with seasonal cheer? Chalk it up to some brilliant marketing.

In 1900, a German immigrant named Albert Ecke was planning to move his family to Fiji. Along the way, they became enamored of the beautiful sights found in Los Angeles—specifically, the wild-growing poinsettia, which was named after Joel Roberts Poinsett, the U.S.-Mexican ambassador who first brought it to the States in 1828. Ecke saw the appeal of the plant’s bright red leaves that blossomed in winter (it’s not actually a flower, despite the common assumption) and began marketing it from roadside stands to local growers as "the Christmas plant."

The response was so strong that poinsettias became the Ecke family business, with their crop making up more than 90 percent of all poinsettias sold throughout most of the 20th century: Ecke, his son Paul, and Paul’s son, Paul Jr., offered a unique single-stem arrangement that stood up to shipping, which their competitors couldn’t duplicate. When Paul III took over the business in the 1960s, he began sending arrangements to television networks for use during their holiday specials. In a priceless bit of advertising, stars like Ronald Reagan, Dinah Shore, and Bob Hope were sharing screen time with the plant, leading millions of Americans to associate it with the holiday.

While the Ecke single-stem secret was eventually cracked by other florists—it involved grafting two stems to make one—and their market share dwindled, their innovative marketing ensured that the poinsettia would forever be linked to Christmas.

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