EarthDate

How long is a second? That depends on how you measure it. In a previous EarthDate, we talked about how people divided the day into 24 hours, then hours and minutes into 60. That made the second 1/86,400th of a day. But how long is a day? Turns out, that’s not constant. Earth wobbles slightly on its axis, changing its rotation time. So scientists settled on a year, reasoning the day’s length would...

Each winter in the Northern Hemisphere, it feels like Earth is drifting farther away from the warmth of the Sun. In fact, it’s just the opposite. When we measure the size of the Sun in our sky, we find that it actually appears 3.4% larger in winter—because it’s 3.4% closer. More than 3 million miles closer. The Sun is about 95 million miles away in summer, but just 92 million in winter. And this i...

You’ve probably heard that no two snowflakes are alike. And mostly, that’s true. Snowflakes aren’t formed from freezing water, but when water vapor freezes, skipping the liquid stage altogether. This allows the water molecules to organize themselves into the snowflake’s delicate structure. Snow crystals come in more than 30 basic shapes, with the classic star-shaped snowflake forming best in tempe...

The waterfall. In concept, it’s simple: just water… falling. But in life, waterfalls are a wonder. Beautiful, frightening, powerful, calming, deafening, soothing—sometimes all at once. They’ve been inspiring humans for millennia. When water flows over a wide shelf, it’s called a block falls. The widest is Victoria Falls in Zambia, over one mile across. Called “smoke that thunders” in the local lan...

We have 10 fingers, so we’ve based our common counting systems on 10. Why then, do we divide the day into 12 hours and the hour into 60 minutes? To understand, we need to go back 3000 years. Babylonians also used their hands to count, but wanting to count higher than 10, they devised a different system. They used their thumb to count the three segments of their four fingers to get 12. They marked...

Imagine walking down a beautiful tropical beach. You spot a fruit on the sand, like a plum or small ripe apple. It smells sweet, so you wash it in the water and you’re about to take a bite… But wait! You may have in your hand a Death Apple, the fruit of the manchineel, a tree that’s relatively common to the tropical beaches of the Americas. Despite its good looks, the manchineel is listed in the G...

Earth has experienced dozens of ice ages in the past few million years. At the coldest point of the most recent one, ice sheets over a thousand feet thick covered much of North America. Then, 15,000 years ago, the world began to warm, and ice started melting—until 13,000 years ago, when Earth plunged back into the Ice Age for a thousand more years. Scientists thought this may have been caused by t...

Greenland is Earth’s largest island, and most of it is covered by ice up to 2 miles thick. Scientists decided to investigate the age of this ice sheet and were surprised to find that not that long ago, there wasn’t one. They used ice cores to date different areas, then flew planes over it with special ice-penetrating radar. The radar identified bands of softer and harder ice and layers within them...

X-rays are common today, but their accidental discovery 125 years ago was celebrated around the world as a scientific miracle and earned Wilhelm Röntgen the first Nobel Prize in physics. Röntgen was working in his lab in Germany, trying to replicate the experiments of other scientists with an electrified cathode tube, when he noticed some barium-painted cardboard nearby fluorescing. Puzzled, he tu...

In a previous EarthDate, we told you about the accidental discovery of X-rays in the late 1800s. Scientists around the world began to experiment with them. Thinking them no more harmful than visible light, they did so without protection… sometimes with disastrous results. Early researchers would place the emitter in the center of the room, hold up their hands, and—using special lenses to examine t...

Earlier, you heard how geckos have a sticky superpower. Microscopic hairs on their toes generate electromagnetic attraction to the surfaces they walk on, letting them run up glass and across ceilings. Anoles—common garden lizards in the southern U.S.—have less stick. They can dash up trees but can’t cling to the underside of things. Their electromagnetic attraction evolved separately from geckos’....

They may not go into polling booths and come out with an ‘I Voted’ sticker. But most animals that live in groups have developed ways to make collective decisions and act together for the good of one and all. English rock ants are always scouting for a new nest. When a few individuals find the same new spot, they seem to agree that this real estate has potential. So they go back to the current nest...

Wondering what to get that special someone for Halloween? How about a bouquet of corpse flowers? Of course, you’ll have to go all the way to Indonesia to get them. And it would be a very, very large arrangement. There are two types of corpse flowers, and both emit a strong odor of rotting meat to attract flies and beetles to pollinate them. Titan arum lives up to its name, with flowers topping 10...

Phoenician soldiers, when injured in battle, would shave bronze from their swords into their wounds. Why? For the copper. Copper is often found in its pure state, rather than bound in ore, and is easy to bend. This made copper the first metal to be shaped by humans into useful implements around 10,000 years ago. The Copper Age lasted 5,000 years, until someone realized they could add tin to copper...

Have you ever seen a gecko walk straight up a glass door, or sprint upside down across a ceiling, and wonder, “How can they do that?” To get the answer, you’d need an electron microscope. At 200× magnification, you’d see the gecko’s toes are covered with tiny hairs called setae. Zoom in closer and at 1000×, you’d see that the setae are actually bunches of hairs, like in a hairbrush. Much closer, a...