Before there was a Global Positioning System (GPS) receiver in every car (or in the backpacks of wayward hikers), there was the magnetic compass. In fact, before there were cars and nylon backpacks, explorers and sailors and pirates used their trusty compasses to find their way around the big, featureless ocean. Even on a cloudy night, with no stars to guide you, a small piece of magnetized metal, mounted so that it could swing freely, told you which way was north.
What’s so special about north? If you know where north is, you know it all. Face north, and south will be behind you, east on your right, and west on your left. Rotate a handheld compass, and the needle, strangely, doesn’t turn with it.
Feeling an attraction we’re unaware of, the floating metal needle moves on its own, like the pointer on a spooky movie Ouija board. The needle seems drawn toward some distant beacon, feeling the pull even through walls.
But the needle on a compass isn’t made of just any old metal. Instead, it’s a metal that’s been magnetized. This slender, lightweight magnet has its own north and south poles, which are attracted to the opposite poles of other magnets. Meanwhile, the magnet is free to pivot in any direction.
Luckily for lost travelers (especially before GPS tracking in cell phones and cars), the planet we travel on is itself a magnet. Pocket compasses respond to Earth’s magnetism by lining up in its magnetic field. So even on a cloudy night, with no stars to guide him, a sailor adrift in a dark sea can find “north”—and thus south, east, and west.
(The Earth’s field reverses itself every 500,000 years or so, but for now, Earth’s “south” pole is in the north, its “north” pole in the south. Which is why a magnetized needle’s north pole, attracted to its opposite, will point north. About 800,000 years ago, compass needles would have pointed south.)
Human beings have used compasses to navigate for more than 2,000 years. The earliest compasses were made of wood, topped with a bit of lodestone, a naturally magnetic iron ore. Floated on water or other liquid, the wooden compass was free to move, the lodestone turning until it aligned itself with the Earth’s field.
Scientists think that the Earth’s magnetic field is generated by looping electric currents in our planet’s (superhot) liquid metal core. Imagine a bar magnet stuck vertically through the center of the Earth, its invisible field arcing out into space like a horizontal figure 8.
Although we don’t notice it, magnetized objects feel its pull.
But while the Earth is large, its magnetic field is rather feeble. Our planetary magnet is thousands of times weaker than the magnets on your refrigerator, which can keep class photos and shopping lists clasped to the metal door (or grab a stray paper clip if it comes too near).
The Earth’s magnetic field varies across the planet, but it’s strongest at the poles. Magnetic strength is usually measured in gauss or tesla units. At its weakest, in parts of South America, the Earth’s field strength is about 0.3 gauss (30 microteslas). Near the north and south magnetic poles, the strength increases to about 0.65 gauss (65 microteslas). By contrast, that small, cow-shaped magnet on your refrigerator may be 50 gauss (5,000 microteslas) strong. So it’s no wonder that the Earth’s weak magnetism can’t make paper clips migrate en masse to the poles.
Autumn’s cool days are trimmed with deep blue skies and golden light, and brilliant leaves of yellow, orange, and red. Leaves changing color in the fall are a tree’s way of preparing for long winter, rather like how we put up storm windows and pull warm clothes and blankets out of storage.In summer, the leaves on trees like pin oaks and sugar maples are green, because they are chock-full of the green pigment chlorophyll.
Trees need sunlight to produce chlorophyll. In turn, chlorophyll uses sunlight’s energy to split water (H2O) into hydrogen and oxygen. Meanwhile, leaves also absorb carbon dioxide gas from the air. The end products of leaf chemistry: carbohydrates (homemade plant food for the tree), and oxygen, released into the air (the gas we need to breathe). The whole process is called “photosynthesis.”
Along with green chlorophyll, most leaves also contain yellow, orange, and red-orange pigments, the carotenoids. Trees don’t need light to make carotenoids. Botanists call them helper pigments, because carotenoids absorb some sunlight and (nicely) pass the energy along to chlorophyll. We don’t see much of these deputy pigments (carotene, lycopene, and xanthophyll) in summer, because they are masked by abundant green chlorophyll.
But the ever-shortening days of fall mean less daylight and colder weather. The average tree is rushing to save all the nutrients it can for its winter hibernation. Nitrogen and phosphorus are pulled from leaves for storage in branches. A layer of corky cells grows between the leaves’ stems and their branches, reducing the leaves’ supply of nutrients and water.
With diminished sunlight, water, and nutrients, chlorophyll synthesis slows. But old, worn-out chlorophyll breaks down at the usual rate—ironically, sunlight destroys it—so each leaf’s stock gradually dwindles. In many trees, as the green fades, yellow and orange pigments emerge from hiding. (These include carotenes, the pigments that color carrots orange.)
But red and purple pigments first form in leaves when the weather turns chilly, tinting leaves of some trees scarlet and burgundy. (The pigments are anthocyanins, which also make radishes red, eggplants purple, and blueberries blue.) Botanists have long wondered why some trees are genetically programmed to manufacture anthocyanins in the fall. New research indicates that anthocyanins may be a tree’s own sunscreen.
Anthocyanins are made in a leaf’s sugary sap, with the help of lots of sun and cool temperatures. Botanists think that anthocyanins shield the leaves’ fading photosynthesis factories from too much sunlight, rather like the pigment melanin protects our skin from the sun. While the red pigments act as a shield, the tree feverishly breaks down and pulls nutrients out of leaves and into its limbs and trunk, before the leaves drop or die.
Anthocyanins may also act like vitamins C or E, scavenging so-called free radicals before they can do oxidizing damage to a fall leaf’s fragile structure.
Upper and outer leaves tend to be reddest, since they are most exposed to sunlight and cold. In some trees, like sugar maples, the reds of the anthocyanins combined with the yellows of the carotenoids make especially brilliant orange leaves.
The color that leaves turn is mostly inherited, like our hair color. But whether these colors are dull or bright depends on the weather.
The deepest, most brilliant shades develop after weeks of cool, sunny fall weather. For example, when the temperature drops to between 32°F and 45°F (0°C and 7°C), more anthocyanins form. In the United States, the ideal weather for stunning foliage is found in places like Vermont.
As autumn fades to winter, the colors fade, too, and leaves loosen from their moorings. Leaves are held to branches by their stems. As the weather cools, the cells at the end of each stem fall apart. Eventually, each leaf is held to its branch only by the thin veins through which water and nutrients once flowed. A light wind or rain can break these flimsy threads, sending the leaves drifting to earth in a carpet of color.
The yellow and red pigments may stay in the leaves for days after they have fallen to the ground. Gradually, though, the colorful pigments disintegrate. All that’s left is the tannins—brown chemicals that also color tea.
The now-brown leaves, cut off from their water supply, dry up. Picked up by the wind, they whirl through the air in leafy cyclones, and crackle underfoot on Halloween.
Camels, unlike people, fit into dry lands like a hand into a glove.
A camel’s body is ideally suited to the extreme dryness and the extreme temperature swings of desert living: daytime heat, nighttime cold, fiercely blowing sand, and little access to water.
We think of camels as plodding through the deserts of countries like Saudi Arabia. But surprisingly, the (rabbit-size) ancestors of modern camels evolved in North America, around 45 million years ago. Over millions of years, goat-size and larger camels evolved. Camels lived all over North America, from Canada to Mexico.
In fact, eight different kinds of camels lived in what is now California. One of these was the towering Titanotylopus, which stood 11.5 feet tall at the shoulder and foraged for food along the California coastline 3 million years ago. Scientists have also discovered fossils of another giant camel who lived in the Arctic forests of northern Canada.
Camels spread out from North America into South America and across the Bering Land Bridge, which then connected North America with Asia. By 7 million years ago, camels had spread all the way to what’s now Spain.
But by 10,000 years ago, camels in North America were extinct, perhaps as a result of changing habitat, human settlements, and hunting.
Today, there are only two living species of true camels. Two-humped Bactrians live in Central Asia. One-humped dromedaries roam the Horn of Africa and the Middle East.
All camels have long, thick, curling eyelashes, no mascara required. The fringe neatly catches blowing sand, keeping it out of a camel’s big brown eyes. Camels also have a third eyelid, which slides closed from the side. In air full of blowing sand, a camel can shut her (very thin) third lid, and still see well enough to trudge on.
A camel’s jutting brow bones and bushy brows shade her eyes from blinding desert sun. Her flaring nostrils can shut tight against windborne sand. And her small, furry ears help keep out annoying ear sand.
Next, a camel’s temperature automatically adjusts to the air temperature, falling as low as 93°F during cold desert nights, then rising to nearly 106°F during the searing days (whenthe temperature can soar to more than 125°F). With the difference between body and air temperature minimized, the air doesn’t heat a camel’s body as much as it would a cooler body, like ours.
Water is essential to all life on Earth, and camels can’t survive without it. Blood is 91 percent water. If water is lost—through sweating and urination, for example—and not replaced, the blood thickens. Instead of streaming through blood vessels, it moves like molasses.
That’s dangerous, because quickly flowing blood helps cool the body. How? As the body converts food into energy, heat is produced. Blood heats up from these reactions deep in the body, carrying this heat as it streams up to and through the skin. Presto: The skin radiates the heat into the air. Result: The body stays cool. But honey-thick, dehydrated blood can’t get to the skin fast enough. Heat builds up; death may follow.
Even in the coolest weather, human beings can live only a few days without water. Camels, however, can survive for up to 17 days between drinks.
A camel’s metabolism—the speed at which its body burns food—slows during hot weather,making for less body heat.
Camels have also evolved a way to recycle water from their kidneys, funneling it to one of three stomach compartments and then back into the blood. But there’s more: If you look at a camel’s blood under a microscope, you’ll see that the red blood cells are oval rather than round like those of other mammals. The streamlined shape allows oxygen-carrying cells to ease through vessels—even when a camel is dehydrated.
Finally, there are those humps. Although a camel’s hump isn’t actually full of water, it does keep a camel cooler in hot weather. Packed inside the humps are fat, up to 80 pounds in a single mound. How does all that extra padding help on an afternoon when it’s 120° F? The hump acts as a protective hood. Baking in the desert sun, the mound of fat absorbs and traps heat, slowing its descent to the camel’s vital internal organs. Meanwhile, the rest of a camel’s body— especially those thin, spindly legs—radiates heat into the air.
But above all, the hump is a camel’s emergency food supply, like a hiker’s backpack stuffed with trail mix, turkey jerky, and energy bars. A hump (or two) allows a camel to survive for several weeks without actually eating. As the fat is burned for energy, the hump gradually shrinks, becoming flabby and floppy.
The next time you get on an elevator in the lobby of a tall building, close your eyes. As the box you’re riding in smoothly ascends, you may feel like you’re not moving at all—at least, until it slows to a stop at your floor. Think about it, and you’ll realize you’ve had the same experience in a train or a car. Or even on a jet plane, traveling through the clouds at more than 500 miles per hour.
We’re traveling on our planet, too, circling the Sun, journeying through space with the rest of the solar system, all while Earth spins on its axis like a top.
In fact, our planet’s rotational speed at the equator is higher than a commercial jet’s cruising speed. The Earth measures about 24,900 miles around at its widest. Divide that by the 24 hours it takes to turn once, and we get the Earth’s speed at the equator: a dizzying 1,040 miles per hour.
But since the distance around the planet shrinks as we travel toward the poles, the relative speed changes, too. So at the latitude of New York City, the Earth’s rotational speed is about 783 miles per hour. Which means that each second (“one hippopotamus, two hippopotamus”) you’ve traveled 1,148 feet forward on your planetary merry-go-round. And as in a plane at constant speed, you’re just not feelin’ it.
Physicists discovered this principle centuries ago: In a closed box, no windows to peek from, there’s no way to tell whether we’re stopped still, or moving at an unvarying speed.
But if the “box” (or elevator, or plane) speeds up or slows down, the feeling of movement suddenly appears, too. We experience motion when it’s changing.
Since Earth’s rotational speed is so constant, we (thankfully) can’t feel how fast we’re really spinning. The same goes for our 365-day trip around the Sun, which our speedy planet whizzes through at 67,000 miles per hour.
Although you’re being spun to the east at, say, nearly 800 miles per hour, the matter in your body is strongly attracted to the much greater mass of matter of the planet. The centrifugal, outward “force” created by rotation is a tiny fraction of the strength of our planet’s downward-directed gravitational force.
But if the Earth’s rotational speed changed suddenly, we’d realize we’re moving at breakneck speed. If the Earth suddenly slowed, scientists say, we’d tumble forward; if it sped up, we’d fall over backward.
And if Earth’s rotational speed at the equator increased to more than 18,000 miles per hour, with a day lasting just 80 minutes, gravity could no longer keep us safely planted to the ground. And we would, indeed, go flying off into the dark.
Why is the Sky Blue?
The sunlight that lights up the daytime sky is white. So why isn’t the sky a brilliant white? In order for the sky to look blue, something must be happening to the light as it passes through Earth’s atmosphere.
When white light streams in from the Sun, it zips from the near vacuum of space into the gassy atmosphere blanketing our planet. While Earth’s air contains traces of many gases, from carbon dioxide to argon, nitrogen (at 78 percent) and oxygen (21 percent) make up most of the atmosphere. And when photons of sunlight encounter the gas molecules of Earth’s air, they are changed by the encounter.
Where does the blue come from? Actually, the blue was in sunlight all along. White light is made of a concealed rainbow of colors, revealed when a beam of sunlight passes through a prism. Then we see the familiar rainbow spectrum: red, orange, yellow, green, blue, indigo, violet. Each color is a different energy and wavelength.
The air’s gases tease these colors out of white light. Some sunlight simply zips through the empty spaces between gas molecules, reaching the ground intact. But light that has a run-in with gas molecules is absorbed, split into its true colors, and then scattered every which way.
How does it work? A gas molecule’s member atoms get excited by the photons (particles) of light, and re-emit photons in distinct wavelengths—from red to yellow to violet. The light then heads on toward the ground or is sent out sideways into the sky. Depending on the angle, some light even zooms back into space.
And here’s how the sky turns blue: The shorter-wavelength blue-to-violet end of the sunlight spectrum is scattered much more than the reds and yellows. So we see blue light from every direction in the sky, overpowering fainter red, yellow, and orange.
Interestingly, violet light is scattered by gas molecules even more strongly than blue. So why don’t we see a sky awash in purples? According to physicist Jearl Walker of Cleveland State University, there are two explanations: The violet part of sunlight is dimmer than the blue, and human eyes are less sensitive to shorter-wavelength violet.
It may be a different story for others living on Earth. Since the eyes of animals are sensitive to different wavelengths of light, it’s likely that many animals perceive Earth’s sky in different hues. Honeybees, for example, can see all the way into the spectrum’s invisible-to-us ultraviolet. To a bee, the sky may be tinted purple.
For us humans, during the daytime, the blue stands out, intensified by the black backdrop of space behind the sunlit atmosphere. But where does the blue go at night? While the Sun is below the horizon, Earth’s sky is still just as full of gas, scattering the light that remains. According to Walker, the night sky is indeed still blue. But the blue is simply too dim for our eyes and brain to perceive. However, a camera set for a long exposure—collecting light for several minutes to several hours—can reveal the deep, true blue of a starry night.
Is this the longest article on this AWESOME site!? Takes a while to read, but it was very informative.