Science for Kids — August 11: Cosmic dust, spider catapults, and fish who know your face

Professor Pip adjusted his slightly crooked spectacles and gazed up at the darkening sky. "Ah! Mia, Leo, Asha — come quickly. Tonight we chase a very sneaky idea."

Three children scrambled up the grassy hill and plopped down in the cool grass beside a small brass telescope. Beside it, Pip had set a warm lantern glowing on a stump.

"Far, far away," Pip began, his fluffy tail swishing, "there is a dying star. It is huffing and puffing out enormous waves of hot radiation — invisible light so strong it can pop dust right out of existence. Poof!"

"Poor dust!" said Mia.

"Ah — but here's the sneaky part," said Pip, pulling a small paper umbrella from his pocket. "Some of the dust is surviving. Watch this."

He held up the paper umbrella between the lantern and Asha, and a soft dark shadow fell across her lap.

"Ooh, it's dark right where the umbrella points!" said Asha.

"Precisely! The umbrella blocks the light. And it also protects whatever's behind it. That dark, calm spot is a shadow. Now — imagine a tiny fluffy clump of dust in space, out near that dying star. If the clump is dense enough, it makes its own shadow. And guess who gets to hide in that shadow?"

"The dust behind it!" cried Leo, bouncing on his knees.

"Exactly right, my fellow scientist! The clump takes the beating on its sunny side, and behind it, all the way in the cool dark shade, more dust stays safe."

Pip pointed up. "The Webb Space Telescope just photographed hundreds of these little dust umbrellas around a star called the Lion Nebula. Each one trails a long tail pointing away from the star — like tiny cosmic comets."

"Like when I stand in the shade of the big oak tree at recess!" said Mia.

"Just like that. And here's the wonder: someday, that shielded dust may drift out into space and gather into new stars and new planets. So a star dying now is helping to build the stars of tomorrow."

The children looked up at the pink-purple sky. Pip's spectacles slid down his nose as he handed each of them a paper umbrella. "Now — I wonder how many places in your day you can find a shadow doing important work?"

Professor Pip crouched low in a sunny rainforest clearing, his forest-green lab coat dusted with moss. From a bulging pocket he pulled out a bent green twig, a rubber band, and a small brown acorn.

"Gather round, gather round," he whispered. "Today we honor a tiny genius with eight legs."

Sofia and Theo tiptoed over, mouths already open with curiosity.

"Watch closely." Pip bent the springy twig into a wide arch, hooked the rubber band across it, and rested the acorn in the middle. He pulled the twig back — back — back — his tail quivering with the strain.

"Three... two... one—"

He let go. SPROING! WHOOSH! The acorn zoomed into the sky and plopped into a fern.

The children burst into giggles.

"That," said Professor Pip, adjusting his crooked spectacles, "is stored energy. When I bent the twig, I squished energy into it — like squeezing a spring. It wanted to snap back. As soon as I let go — whoosh — all that energy jumped into the acorn."

"Ooh," said Theo. "Like when I pull back a swing and let go?"

"Precisely, my clever friend! Now here is the astonishing part. In a rainforest not so different from this one, scientists just discovered a spider — a tiny one, smaller than your fingernail — that builds a catapult almost exactly like mine. But instead of a twig, she spins sixty long silk lines and pulls them all as tight as harp strings. It takes her four whole hours."

"Four hours?!" said Sofia. "That's longer than lunch!"

"Longer than lunch and nap time. Then — and this is the sneakiest bit — she paints the trap with a sweet perfume that green tree ants love. An ant marches up, takes a big brave bite... SPROING! The whole cone snaps loose, and the ant sails through the air right into her waiting web."

"So she never even has to chase it!" cried Theo.

"Exactly right! The ants she hunts are fierce — they'd bite her back if she went near their nest. So instead, her stored energy does the hard work for her. Scientists are calling her the ballista spider, after the giant catapults the ancient Romans used."

Pip looked up at the leaves swaying above. "A spider small enough to sit on your thumbnail, my friends — inventing a machine that took humans thousands of years to build."

He handed Sofia and Theo each a springy little twig. "Now — I wonder what you can launch?"

Professor Pip stood at the end of a sun-warmed wooden dock, a bright red neckerchief tied jauntily over his forest-green lab coat. Below him, silvery fish flickered in the turquoise water.

"Beatrix! Jun! Come, come — today we learn how a fish notices you."

The children padded onto the dock in their swimsuits, life vests bobbing.

"Now," said Pip, pulling two small paper cards from his pocket — one printed with a red star, the other with a blue triangle. "I want you to remember: I brought a snack for the fish, but only when I hold up the RED star. Ready?"

He waved the red star, and — plop! — dropped a tiny crumb into the water. The fish rushed to snatch it. He held up the blue triangle and dropped nothing. Then red star — crumb! Then blue — nothing. Then red — crumb!

After a while, Pip held up the red star with no crumb at all. The fish rushed up anyway, mouths popping open at the surface.

"Look!" gasped Beatrix. "They came just because they saw the red!"

"Precisely!" said Pip, his tail swishing with delight. "They learned. When their brains linked the color red to a snack, they started reacting to the red all by itself. That's called learning by association — connecting one thing to another because they keep happening together."

Jun frowned thoughtfully. "But those are fish. Fish are supposed to have three-second memories, right?"

"Ah!" said Pip, adjusting his crooked spectacles. "That, my friend, is one of the biggest myths in the sea. This very month, scientists in the Mediterranean discovered that wild fish — ocean fish, not aquarium fish — can remember which human feeds them. When one diver wore a bright red vest and brought snacks, twenty fish followed her every day. When a second diver appeared, the fish learned to ignore him because his outfit was different."

"Oh! Like they picked out the diver by her uniform!" said Beatrix.

"Exactly right! The fish weren't looking at her face — they were reading her colors and patterns, the same way you might spot your friend across the playground by their favorite jacket. When both divers wore the same suit? The fish got completely muddled."

Pip looked down at the shimmering fish, tail curling with wonder. "For hundreds of years, humans thought fish were simple little creatures. But down there, my friends, they are watching us. Learning us. Remembering us."

He handed Beatrix and Jun each a shiny colored card. "Now — I wonder: if you visited the same pond every day for a week, do you think the fish would start to notice you?"