Today is Wednesday, so it’s time for our regular feature What is that? Here’s today’s term:
Light Year – a unit of length used to measure great distances in space
Light Year is a confusing term. We all know what a year is. A year is the length of time from your birthday to your next birthday. It is also the length of time it takes the Earth to travel around the sun one time. That idea may help us.
A year measures time. It is how long the Earth takes to travel around the sun. We could make up a term called an Earth Year. It would mean how far the Earth travels in one year — or how far that trip around the sun is. By the way, that is about 584,000,000 miles. (If you live anywhere besides the United States, then that is about 940,000,000 kilometers.)
If an “Earth Year” (my made up term) is how far the Earth travels in one year, then a Light Year is how far a beam of light travels in one year. Light travels very, very fast. It can travel from the sun to the Earth in about 8 minutes. That is about 92,960,000 miles (149,600,000 kilometers). It takes me more than 8 minutes just to run one mile.
Light also travels at a constant speed in the vacuum of space. (It does slow down when it passes through air, a window, or water. But even then, it travels super fast. Michael Phelps is fast in water, but light is still faster.) In the vacuum of space, light does not get tired and stop flying along.
Because light travels so fast, it travels very far in one year. That makes a Light Year–a measure of distance–very useful for measuring the vast distances between stars. For example, the nearest star to our sun is Proxima Centauri. It is about 25,000,000,000,000 miles away (40,000,000,000,000 kilometers). It’s much easier to say (and to write) 4.25 light years.
So, when someone says “That is light years away,” they mean it is very far. They are not talking about time or how quickly a human could travel that distance. They are just talking about how large the distance is.
Invent your own measurement!
Let’s invent our own measurement of distance.
First, decide what you will use to set your measurement length. Will it be the length of an object? (To measure small distances, we could use the length of a twig we found.) Will it be the distance that something travels? (Like how far you can ride your bike in five minutes?)
What will you use your new measurement length to measure? The length of your hand? Then length of a car? The length of your neighborhood?
Finally, what will you name your measurement length? An “twig unit”? A “bike in 5”? Will you name it after yourself? (A “Matthew Mile”?) Or create a shiny, brand-new name you made up yourself? (A “plenth”?)
Today, I want to focus on cities built beneath the ground. One is a fortress built beneath the frozen crust of a distant planet, and the other is a secret, centuries-old city far beneath New York City.
In Fortuna by Kristyn Merbeth, Corvus is a soldier on the planet Titan, a frozen planet divided by an eternal civil war. Because of the severe cold and the constant fighting, Titans live in caves and in cities built beneath the ground.
In Chapter 18, Corvus is leaving the military and taking a train from Fort Sketa to a fortress city filled with civilians.
“The next morning, I wake early to head to the train for the sake of avoiding unwanted company. The station is just below the surface, chillier than the lower levels of the building, and the ceiling trembles under the weight of activity in the hangar above.
. . . . “When I first arrived on Titan, underground rooms made me feel caged and nervous. Especially so in places like this, where the ceiling occasionally shakes loose clouds of dust, and the rumble of trains along the tracks makes it feel like the whole building could collapse on top of me. Over the years it’s become normal. Now, for the first time in a long time, I wonder if it will feel strange to walk in the sunlight again.
. . . . “The underground fortress of Drev Dravaask is beautiful. It’s warm enough that I take off my outer coat, and not overcrowded with people and buildings like the major cities of other planets. There is a simple elegance to its architecture and a surprising kindness in its people. They all nod or smile at me as I pass, or press their fingers to their hearts if they notice the [military] brand on my wrist. I return the gesture without thought, drinking in the quiet. It’s so peaceful here compared to the rest of Titan. Neither the storms nor the war can touch this place.
There is a simple elegance to its architecture and a surprising kindness in its people.
“Drev Dravaask has held its ground for over a century while cities around it crumbled. The stability allows people to build lives here that do not revolve around war. There are restaurants and shops, bars and inns, families that aren’t missing pieces. Of course, there is also a huge military recruitment center near the heart of the city, and posters advertising the perks of service on every street corner, so it is not possible to forget entirely.”
Sister Scorpia sees Drev Dravaask, the undground city on Titan, very differently
Corvus was born on the planet Titan and returned as an adult to serve his mandatory three-year tour as a soldier in Titan’s eternal civil war. His sister, Scorpia, was born on the family’s spaceship, Fortuna, and has a very different impression of the underground Drev Dravaask. After storing Fortuna in a cave hangar on the surface, Scorpia and her family take a slow, rusty elevator deep into the planet.
“The city of Drev Dravaask is carved into the earth beneath the surface of Titan, dark and damp caves forming homes and businesses and more. The surface of the planet is too cold, too stormy; water freezes up there; and plants won’t grow, and people die slowly and numbly without realizing that they’re dying. Down here, close to the hot springs that run beneath the surface, it’s a handful of degrees warmer.
“It would be easy to be miserable in a city like this, but the people of Drev Dravaask find pockets of happiness in their cold underground world. As we head inward, a trio of soldiers sways past us arm in arm, belting a severely out-of-tune version of Titan’s planetary anthem. A cluster of children giggle in an alleyway, finger-painting dirty words on the walls. A hunched street vendor with a face full of battle scars hands a carefully wrapped meal to a gaunt teenager on the street corner.”
Gregor the Overlander finds a magical city of humans buried deep underground
In Gregor the Overlander by Suzanne Collins, Gregor and his baby sister, Boots, discover a mysterious land, called the Underland, filled with giant, talking rats, bats and cockroaches, that lies far beneath New York City.
Gregor stumbles into the Underland and finds a city hidden deep beneath New York City
“There are but five known gateways to the Underland,” said Vikus. “Two lead to the Dead Land, but you would never have survived those. Two gateways open into the Waterway, but your clothing is quite dry. You are alive, you are dry, from this I surmise you have fallen through the fifth gateway, the mouth of which I know to be in New York City.”
Vikus, a mysterious, bearded man with silver hair and violet eyes, leads Gregor to the human capital of the Underland.
“He followed Vikus down a tunnel lined with stone torches to a small arch filled with something dark and fluttery. Gregor thought it might be more bats, but on closer inspection he saw it was a cloud of tiny black moths. Was this what he had passed through when he stumbled into the stadium?
“Vikus gently slid his hand into the insects. ‘These moths are a warning system peculiar to the Underland, I believe. The moment their pattern of flight is disturbed by an intruder, every bat in the area discerns it. I find it so perfect in its simplicity,’ he said. Then he vanished into the moths.”
Welcome to the city of Regalia!
“Behind the curtain of wings, Gregor could hear his voice beckoning. ‘Gregor the Overlander, welcome to the city of Regalia!’
. . . .
“Gregor didn’t know what he’d expected. Maybe stone houses, maybe caves—something primitive. But there was nothing primitive about the magnificent city that spread before him.
“They stood on the edge of a valley filled with the most beautiful buildings he’d ever seen. New York was known for its architecture, the elegant brownstones, the towering skyscrapers, the grand museums. But compared with Regalia, it looked unplanned, like a place where someone had lined up a bunch of oddly shaped boxes in rows.
“The buildings here were all a lovely misty gray, which gave them a dreamlike quality. They seemed to rise directly out of the rock as if they had been grown, not made by human hands. Maybe they weren’t as tall as the skyscrapers Gregor knew by name, but they towered high above his head, some at least thirty stories and finished in artful peaks and turrets. Thousands of torches were placed strategically so that a soft, dusky light illuminated the entire city.
“And the carvings . . . Gregor had seen cherubs and gargoyles on buildings before, but the walls of Regalia crawled with life. People and cockroaches and fish and creatures Gregor had no name for fought and feasted and danced on every conceivable inch of space.”
Your favorite underground cities
Sci fi has lots more underground cities. Which ones are your favorites? Were they built on Earth, on other planets, or in other universes? Were they built by humans, alien life, or ancient creatures long gone?
In Kristyn Merbeth’s space opera Fortuna, she introduces the spider tank, a sturdy, four-legged machine that can carry a squad long distances over the treacherous, icy terrain of the planet Titan.
The novel alternates between chapters told by Portia, the pilot of the family’s spaceship, Fortuna, and chapters told by her brother, Corvus, who is finishing his three-year enlistment in the military on Titan.
Here, Corvus describes the spider tank:
“The spider tank is designed to travel through dangerous terrain, able to navigate across ice and up almost-vertical cliffs, but the four legs plod along in jerky motions that always sicken my stomach. Even after three years on Titan, I’m still not used to land vehicles, too accustomed to the smoother travel of hovercrafts that are common on every other planet. Here the extreme winds and unpredictable weather make them too dangerous to operate.”
Traditional tanks on earth travel on wheels or on caterpillar treads, like those on a bulldozer.
A tank can really be any heavily armored vehicle with weapons. If it doesn’t have serious weapons, it should probably just be called an armored personnel carrier. Merbeth does not tell us about the weaponry in the spider tank. But in a battle scene, she writes of hand-held blasters and pulse rifles that shoot laser-fire. So I’m imagining the spider tank has some heavy-duty lasers and maybe a few other tricks besides.
Design your own tank!
If you were an engineer of the future, what kind of tank would you build?
Would it have wheels, treads, legs or hoverjets?
Would it fire cannonballs, shells, missiles or lasers?
Would soldiers ride in it, drive it remotely, or would it have artificial intelligence (AI) and drive itself?
Ansible — a machine used for instant communication across vast distances of space.
Sci Fi writers have created many fictional devices that allow people to talk, write, or send messages instantly or very quickly across the vast empty stretches of space.
The legendary Ursula LeGuin created the word “ansible” in her 1966 novel Rocannon’s World. She described a device that could be used to send instant text messages to anyone else with an ansible.
LeGuin used the ansible in later books as well. By the way, “ansible” is a shortening of the word “answerable,” so-named because the device allowed a person to type a question that could get an “answerable” reply in a reasonable amount of time.
Why do Sci Fi writers need a fictional device?
Why did Le Guin need a fictional communication device? Why couldn’t her characters just send messages using an antenna that sends radio waves?
The problem is the speed of radio waves and the great distances between solar systems.
The Speed of Light
In empty space, radio waves travel at the speed of light. According to the great physicist Albert Einstein, nothing can travel faster than the speed of light. Even though his theory is more than 100 years old, it is still hard for most people to understand. That’s probably because in our daily lives, the only thing we see traveling at those speeds is light itself. And individual light particles–called photons–are too small and too fast for us to detect with our eyes.
Light has no mass. It is pure energy. That’s why it can reach such a high speed. But for things with mass–things made out of atoms like you and me and everything we own–we gain mass the faster we travel. At the fastest speeds that humans and machines can travel, the change is barely noticeable. But if you send a ship rocketing through space, the closer it gets to the speed of light, the more its mass grows.
A spaceship floating in space has no weight. But it still has mass. To push it forward faster than it is already traveling requires more energy. Einstein’s law says that the faster you make the ship fly, the more mass it has. That means each time you try to add speed, you need more energy than the last push. Before the ship could ever reach the speed of light, you would run out of energy.
What does the speed of light have to do with communication across space?
In science fiction, we often write and read about people traveling to planets in far away solar systems. It takes years for light–even traveling as fast as light does–to reach a planet in another solar system. That means that a communication system that uses radio waves, light or lasers to send messages to a planet outside our solar system would take years. More than a lifetime, if the planet is not near one of our neighboring stars.
Why don’t Sci Fi writers use something real–some technology that we know–other than light or radio waves to send messages then? Well, because nothing travels faster than the speed of light.
Long distance communication in Sci Fi
It’s hard to write a gripping Sci Fi story if the heroes on a distant planet send an urgent message back home to Earth and then must wait 20, 50 or even a 100 years to receive the reply. Sometimes Sci Fi writers want to tell stories where humans living on different worlds or in spaceships far apart can still talk to each other or communicate in some way.
That’s why LeGuin created the fictional ansible. So her heroes could send messages back home and receive orders from their superiors.
Create your own device!
What kind of fictional device can you imagine to instantly communicate between Earth and a space ship light years away? What would you call it? How would it work?