by Bob McDonald
Unfortunately, no one knows how to warp space enough to move a ship. The gravitational waves that we’ve detected so far are extremely small, so it would take a huge number of them to go anywhere. Maybe someday we’ll figure it out, and then imagine where we might go!
Remember, though, that when a gravitational wave passes through an object, it can bend or distort its shape. When gravitational waves pass through the Earth, then, they cause one arm of the observatory to get a little longer (and then a little smaller) than the other. That makes the mirrors at the end of each arm vibrate. The gravitational waves are extremely small, so the amount the mirrors move is less than the width of an atom. The light detector measures the light waves of each laser as they shift in and out of alignment, making a pattern in the light that vibrates and allowing us to “see” the gravitational waves.
SPACE PLACES
There are two LIGO detectors in the United States: one in Washington State, in the western part of the country, and the other in Louisiana, in the south.
In September 2015, the LIGO observatories both made the first detections ever of gravitational waves when they recorded two black holes colliding. Not only did they see the gravitational waves on their instruments, but they also turned it into sound waves so we could hear the event, too. It turns out that when two black holes collide with each other, they go “WHOOOOOP”!
Since then, scientists have seen other gravitational waves from colliding neutron stars, which are super-dense stars with powerful gravitational fields.
Scientists are excited about this new technology because it opens up a whole new field of gravitational wave astronomy. These waves travel across the entire universe and can tell us about some of the more extreme events in the universe, such as the collision of two black holes, super-dense neutron stars, or maybe even the nature of gravity itself. And since gravitational waves pass through everything, they are not blocked by dark clouds of gas in space the way light is, so we will be able to see farther out into space, and farther back in time, than ever before.
Gravitational waves are like a new set of eyes on the universe. Who knows what we will see?
YOU TRY IT! From Sound to Sight
WHAT YOU NEED
A funnel
A piece of aluminum foil
A flashlight
WHAT TO DO
Take a piece of aluminum foil that is larger than the wide part of the funnel and wrap it tightly over the top so it looks like a drum. Make sure the shiny side is facing outward.
Stand about a meter away from a wall and hold the funnel like a trumpet, with the aluminum side facing toward the wall.
Shine the flashlight onto the aluminum and turn the funnel slightly until you see a circle of light reflected on the wall.
Carefully place your mouth over the small end of the funnel and hum. Watch what happens to the reflection on the wall.
Experiment with different sounds, high and low. Try humming a tune and see how the reflection changes.
Congratulations, you’ve made your own mini-LIGO!
When you hum, you make the air inside the funnel vibrate. That makes the surface of the aluminum foil vibrate, which leads the light waves bouncing off the aluminum to also move. Low sounds are longer waves, so the light should vibrate more slowly, compared to high sounds that vibrate more quickly. If you couldn’t hear the sound, you would still know whether it is high or low by looking at the speed of the vibrating light. Astronomers can tell the same thing about the nature of gravitational waves by the vibrations of the light waves in LIGO.
27 Why Isn’t Pluto a Planet?
Pluto used to be called a planet. Now it’s called a dwarf planet. So what happened?
When you hear the word “planet,” you probably think of Mars, Venus, or the Earth—planets that are made of rock. Maybe you think of giant Jupiter or beautiful Saturn—huge balls of gas hundreds of times bigger than Earth. You might even imagine the bluish-green worlds of Uranus and Neptune, which are also made of gas.
But the oddball planet out there beyond Neptune is a tiny, frozen world—Pluto! Named after the Roman god of the underworld, it’s a dark place, so far away that the sun is just a small, distant star in the sky. Daytime on Pluto would seem like early evening just after sunset on Earth. That also makes Pluto cold—colder than anyplace you can imagine.
This little ice world is very small. You could drop the whole planet onto the Canadian prairies and it would fit between the cities of Calgary and Thunder Bay. And it’s very far away. All the other planets, including the Earth, go around the sun in almost perfect circles. But Pluto follows a noticeable ellipse, which is sort of a football-shaped orbit. It’s also a very big orbit. One year (or one orbit) on Pluto is 248 years on Earth. In fact, Pluto hasn’t even gone around the sun once since we discovered it.
Not only that, Pluto’s football-shaped orbit is so lopsided it crosses the orbit of Neptune. Don’t worry, they won’t run into each other because the other weird thing about Pluto’s orbit is that it’s tilted on an angle—it goes above and below the other planets, as well as in and out.
When Pluto was discovered about ninety years ago, it was thought to be the only planet of its kind. But since then, many other icy planets very much like Pluto have been found in the same region of space. That’s why people are saying Pluto shouldn’t be called a planet at all.
There are thousands of snowball objects surrounding our solar system in a huge swarm called the Kuiper Belt, named after Dutch American astronomer Gerard Kuiper. These ice worlds are believed to be leftover stuff from the giant cloud of gas and dust that formed all the planets and moons billions of years ago. That makes them really interesting to study because they haven’t changed much in all that time. Looking at these snowballs is like looking at the past, to a time before the sun was even born.
Pluto sits right in the middle of the Kuiper Belt. If Pluto remained a planet, we would have to classify all the other icy objects in the Kuiper Belt as planets as well. Can you imagine trying to remember the names of thousands of planets? That’s why Pluto was renamed a dwarf planet, which means a celestial body that still goes around the sun and may have moons, but is small and part of a swarm of other, similar objects. We can think of Pluto as king of the dwarves!
Most planets are fairly easy to spot in the night sky. They tend to be a little brighter than the stars, and if you watch them for a period of time—say, over a couple of weeks or a month—they change their position. They seem to wander among the stars, which is what the word “planet” actually means “wanderer.”
But Pluto, small and so much farther away than the other planets, is not very bright. It looks just like a dim star, even in a telescope. And because it’s so far away from the sun, it moves very slowly, which is why Pluto was the last planet to be discovered. And doing so wasn’t easy.
Can you tell the difference between those two photos below? Notice the little arrows—they point to the only dot that is in a different position.
That is exactly how a young astronomer named Clyde Tombaugh discovered Pluto in 1930. He used a small telescope at Lowell Observatory in Arizona to take pictures of the sky, then he compared his photos to old pictures of the same areas of sky that had been taken before. While flipping back and forth between old and new pictures, he saw what looked like a star that had moved. It took Clyde about seven thousand hours before he finally spotted the tiny little wanderer beyond Neptune, now known as Pluto.
Only one spacecraft has ever visited Pluto. The New Horizons probe, about the size of a piano, took nine years to cross the solar system, then whizzed by the dwarf planet in one day in 2015. But what a day it was!
It’s cold out there on the edge of the solar system, six billion kilometers away from the sun. A warm day on Pluto is about 230 degrees Celsius—below zero! The New Horizons probe confirmed Pluto’s small size. The planet is only about two-thirds the size of our moon.
Pluto has a moon called Charon that’s half as big as it
is. Usually, a moon goes around a planet, but Charon is big enough that both it and Pluto go around each other like a pair of figure skaters. So, in a sense, Pluto is actually a double planet, with two parts to it spinning around each other. Both Pluto and Charon are made mostly of ice—two snowballs circling each other in deep space. Four other little moons around Pluto—Hydra, Styx, Nix, and Kerberos—are much smaller and look like they were chipped off of something bigger. Maybe they were!
Pluto has an atmosphere, but you would choke if you tried to breathe the air. It is made of methane, which is a natural gas we also have on Earth. Imagine air made of the same stuff that cooks hot dogs on a gas stove. The atmospheric methane gives the air on Pluto a blue color. Under that blue sky are steep-sided mountains as high as the Rockies, but they’re made of ice—three kinds, to be exact. There is frozen water, like we have here on Earth. That forms the ground and mountain peaks. Then there’s methane ice that freezes out of the air. When it first forms as frost, it’s bluish white, but after the sun shines on it for a while, it turns reddish brown. Finally, there’s nitrogen ice.
Never heard of it?
Take a deep breath. You just breathed in nitrogen. That’s right, our air is mainly nitrogen gas with some oxygen in it. On Pluto, it’s so cold, our air would freeze and turn into snow. But don’t try to make a snowman out of nitrogen snow. It won’t stay together. Even though it’s white and frozen, it moves like thick pudding. A snowman would quickly drip down and become flat. That’s why there are huge flat plains of nitrogen ice all over Pluto’s South Pole.
After passing Pluto, New Horizons continued farther out into the Kuiper Belt and passed by a much smaller icy world called Ultima Thule, which turned out to be shaped like a snowman! It’s a strange place out there at the edge of the solar system. The spacecraft will eventually leave our solar system altogether to wander among the stars of the Milky Way for billions of years. Its trip has been worth it, though—after Pluto turned out to be such an interesting world, some astronomers suggested it be turned back into a full planet.
The problem of whether Pluto is a true planet or not comes down to how we define what a planet is. We used to think planets were like the Earth—big balls that orbit the sun. Then we found that there are also small things going around the sun, and we called them asteroids and comets. Then we found Pluto and discovered it’s a snowball and there are lots of little snowballs out there with it. So what do we call it? Is it a planet or something else?
Think of it this way. Collect a bunch of different rocks and lay them out according to size. Now, which ones do you call rocks, which ones do you call pebbles, which ones do you call stones, and which ones are boulders? When objects are different sizes, each of us has our own idea of what to call them. And that’s the issue facing astronomers.
Astronomers think there could be two hundred dwarf planets wandering around our solar system. Pluto is one of four named dwarf planets among the Kuiper Belt of icy objects. But others have already been spotted out in the same region and given names, such as Sedna, Quaoar, and Eris (which is actually larger than Pluto). New dwarf planets are being discovered all the time, so there are hundreds of others out there that have yet to be named.
And not all of them are among the snowballs beyond Neptune, either. One dwarf planet, Ceres, rests in the asteroid belt that sits between Mars and Jupiter. Found in 1801, Ceres is simply a really big asteroid, big enough to be considered part of the family of dwarf planets, which makes those who study it happy.
So what’s the final word on when to call something a dwarf planet versus a fully fledged planet? Anything in the solar system that is very large, has pulled itself into a round ball, and that follows its own orbit around the sun should be called a planet. But if it’s small and round and part of a group of other objects that share a path around the sun, it’s a dwarf planet.
Clearly, our definition of planet has changed a little bit over the years to acknowledge both the big ones and little ones, and dwarves are the new kids on the block. It might seem a little confusing to have names change, but that’s how science works. As we learn new things, we add them to our knowledge base. In space science, we’re still learning about our place in the universe. There’s a whole lot out there that we haven’t discovered yet, so let’s get into space and find out more.
YOU TRY IT! A Sweet and Salty Kuiper Belt
Building a model of the solar system helps us see just how big the Kuiper Belt is.
WHAT YOU NEED
One grapefruit
Two marshmallows
Two Smarties
Four poppy seeds or tiny pebbles
Sugar or salt
WHAT TO DO
This is best done on a dark table, desk, or countertop. Place the grapefruit on the table to represent the sun. Place the seeds around the grapefruit, each one a little farther away to represent the rocky planets Mercury, Venus, Earth, and Mars.
Place the two marshmallows farther away to represent the giant gas planets Jupiter and Saturn. Two Smarties represent the big planets Uranus and Neptune at the outer edge of our solar system. (The planets do not have to be in a straight line. That rarely happens in space.)
Finally, sprinkle sugar all the way around your solar system model in a ring that is larger than the distance Neptune is from the grapefruit.
Congratulations! You have just made a (delicious) model of the solar system! The sugar represents the Kuiper Belt. Now try to pick up just one grain of sugar or salt on the end of your finger. That’s Pluto.
Also, keep in mind that this model is only showing the size of the planets, not the distance between them. If we were to spread them out to the full scale of our solar system, the sugar would be several blocks away from the grapefruit.
28 Why Do Stars Twinkle?
Stars don’t actually twinkle. Astronauts in space look out into the night and see stars that are perfectly still—no twinkling, and no change in their light. It’s only when we look up at the stars from the ground that we see them shimmering. That’s not because the stars themselves are suddenly winking at us—it’s the air above us that is moving.
On clear, dark nights, when the stars shine like diamonds in the blackness, it’s easy to forget that we are gazing through a thick layer of air that is always over our heads. The Earth’s atmosphere is like a window we must look through to see out into space.
Unfortunately, our air window is not perfectly clear. Just as the windows of a car or bus are hard to see through when it is raining or when the windows are dirty, our air carries moisture, which we sometimes see as clouds, along with dust, and, sadly, pollution.
Air is also moving all the time, which is why we feel wind, and some air is hot, so it rises. On really hot summer days, if you look down a long road or a city street a block or two away, you might see the pavement shimmering. That’s the air rising up, heated by the hot pavement. As it moves, it distorts the light coming to your eyes so the road seems to be moving when it really isn’t.
You can also see the shimmering air effect if you’re sitting around a campfire and look at people on the other side of the flames. Their faces will seem to be moving because of the distorting hot air rising off the fire.
All of that movement and congestion also gets in the way of starlight. Our eyes are seeing starlight after it has passed through that air junk and activity to reach us. As the starlight streams down from space, the moving air interferes with the light, which causes the shimmer effect that we see as twinkling.
Twinkling stars look nice. We even write songs about them, like “Twinkle Twinkle, Little Star.” But for astronomers trying to see the stars through telescopes, that twinkling is a big headache because all that shimmering gets in the way of taking clear pictures. The stars we see from Earth are moving around, so images in our cameras are always a little blurry. That’s why big telescopes are usually on top of mountains. Up that high, they’re above a lot of the moisture and pollution, so the stars don’t twinkle as much
.
Of course, the best way to bypass the twinkling effect is to put a telescope in space, where it’s completely above the air. From that vantage point, the stars will not twinkle at all. That’s why the Hubble Space Telescope takes the clearest pictures of any telescope. It’s not because it’s the biggest telescope in the world. The mirror on the Hubble telescope is only 2.4 meters (94.5 inches) across. On Earth, some telescopes are being built with mirrors more than thirty meters (1181.1 inches) across. Hubble had to be smaller so that it could fit inside the cargo bay of the space shuttle for launch. But because it doesn’t look through air, its images are stunning. Only the megatelescopes of the future will be able to beat it, and they need a system called adaptive optics to equal the quality of the relatively small Hubble.
There’s one clever way astronomers take the twinkle out of the stars: they make the telescope twinkle, too! Well, not the whole telescope—just a tiny mirror that catches the starlight before it gets to the telescope camera. (Remember, telescopes are just cameras with really big lenses.)
Here’s how it works. After the starlight has gone through the telescope, but before it gets to the camera, the light hits another small mirror that moves just like the stars do. It does so by shooting a laser beam into the sky in the same direction the telescope is looking. The beam shines on the upper atmosphere of the Earth, where it is moved back and forth by the air. As the air moves the beam around, the beam guides the little mirror to move in the same way and at the same speed as the air. That keeps the starlight steady in the little mirror, which then sends it on to the camera. The whole system together then takes the twinkle out of stars so their images are much clearer.
