Nov 12: Why the Sky Is Blue and a Robot Lands on a Comet

Host 1 Welcome to This Day in Science and Discovery for Kids on this day November 12th well imagine a 220 pound metal robot falling toward a comet only to bounce off the surface like a pebble skipping across a pond today we're taking a deep dive into how figuring out the invisible gases above our heads eventually gave humans the tools to reach out and touch icy rocks far beyond our world

Host 2 Yeah. And that journey starts with a boy born in 1842 named John William Strutt. You might actually know him by the title he earned later in life, Lord Rayleigh.

Host 1 Right. And he didn't have the easiest start, did he? Like he started at the famous school called Eton at age 10, but health issues kept him confined mostly to the sick room.

Host 2 Exactly. He eventually had to study from home with private tutors. But that limitation it actually became his greatest advantage.

Host 1 Oh really?

Host 2 Yeah.

Host 1 How so?

Host 2 Well, instead of relying on huge expensive university laboratories later in life, he just learned to rely on himself. He built a simple lab right in his family home and it was there in 1871 that he cracked one of the oldest mysteries in human history.

Host 1 Which is why the sky is blue? okay let's unpack how he figured this out the air around us is full of invisible gas molecules right and sunlight which looks white is actually a mix of all the colors of the rainbow

Host 2 right exactly and light travels in waves the colors all have different wave shapes so red light travels in long lazy waves while blue light travels in short tight choppy waves

Host 1 so think of red light like a giant monster truck that just rolls right over the gas molecules in the air without even noticing them

Host 2 that is a great way to picture it

Host 1 yeah but blue light is like a tiny bumper car because its waves are so short and tight it catches and you know crashes into almost every gas molecule in the atmosphere

Host 2 Right. And that crashing and bouncing effect is what scientists now call Rayleigh scattering. The blue light hits the gas molecules and scatters in every direction.

Host 1 So when you look up, you see that scattered blue light coming right into your eyes. And using just his simple homemade equipment, Rayleigh kept exploring these atmospheric gases.

Host 2 He did. He even co-discovered a brand new gas called argon alongside a chemist named William Ramsey. He won the Nobel Prize in Physics in 1904 for all this.

Host 1 Which just shows you don't need a giant institutional lab to change how we understand the world. And it proves that kids who miss school for illness can still become great scientists.

Host 2 For sure. And, you know, figuring out how those gas molecules behave on Earth was a necessary first step to leaving Earth entirely. Once we understood atmospheric drag and scattering, we could calculate how to fly through it.

Host 1 Oh, and how to build machines that could survive the vacuum of space where there is no air to slow you down. Which brings us to November 12, 2014

Host 2 Right, when after traveling 4 billion miles on the Rosetta spacecraft, a European Space Agency robot named Philae, say Philae, made the very first soft landing on a comet.

Host 1 It targeted a traveling chunk of ice and dust called comet 67P. Wait, it's always confuses me. If a comet is basically just a ball of icy dust, wouldn't a heavy metal box break right through the surface?

Host 2 You know you would think so if it were falling on Earth but comet 67P is very small which means its gravitational pull is super weak. A heavy metal box on Earth weighs almost nothing out there.

Host 1 Oh so instead of crashing down hard Philae was barely being pulled toward the surface at all.

Host 2 Right so the real challenge wasn't crashing it was floating away. Philae was designed to fire harpoons and ice screws to anchor itself down but the harpoons failed to fire.

Host 1 Wow. So because of that weak gravity this 220 pound robot just bounced.

Host 2 Yep. It drifted and floated above the surface before finally coming to rest in a shadowy spot called Abydos.

Host 1 But being stuck in the shadows meant its solar panels couldn't catch much sunlight, right?

Host 2 Yeah, unfortunately. Still, it managed to run on its batteries for three days, sending back incredible data. It proved the comet has no magnetic field and gave us a close-up look at ancient comet dust.

Host 1 And since comets are leftover ingredients from when the solar system formed, touching one helps scientists learn how our whole neighborhood in space came to be.

Host 2 Exactly. And there were a couple of other big space milestones on this day too. In 1980, NASA's Voyager 1 spacecraft made its closest pass by Saturn.

Host 1 Oh, nice. Snapping photos of its braided looking F ring and discovering three new moons.

Host 2 Yeah. and the next year in 1981 the space shuttle Columbia launched it was the first time a crewed spacecraft had gone to orbit a second time testing out a 50 foot robotic arm built in Canada

Host 1 we started by simply looking up to figure out the colors in our sky and that curiosity eventually pushed us to send robots bouncing across distant comets speaking of that sky did you know that violet light scatters even more than blue light does

Host 2 yeah based on the physics the sky should actually look purple But the sky doesn't look violet because the sun emits less violet light than blue. And our human eyes just aren't built to see violet very well anyway.

Host 1 Thanks for tuning in. See you back here tomorrow.