Space is literally all around us, and it’s notoriously difficult to wrap our minds around it. Given the hundreds of billions of stars and planets that make up our galaxy alone, who can be blamed for a lack of cosmic perspective, even if NASA’s InSight explorer just landed on Mars to send some back? As an astronomer at the Adler Planetarium in Chicago, I spend a lot of time talking with our visitors about their space questions, as well as debunking some persistent misconceptions. These five crop up again and again.
Maybe you’ve seen those videos of weightless astronauts on the International Space Station, gracefully (or sometimes not so gracefully) flipping and floating around, hair aloft, like swimmers in a starry sea. This often leads people to conclude that there’s no gravity up there. “Gravity is an important influence on root growth, but the scientists found that their space plants didn’t need it to flourish,” National Geographic wrote in 2012 of botanical research aboard the space station. A 2018 headline in the Independent similarly described a condition that affects astronauts during “zero-gravity missions.”
In fact, if there were no gravity in space, it wouldn’t be possible for astronauts (or anything) to orbit the Earth. As Newton explained it, gravity is the mutual attraction between any objects that have mass. Here on Earth, we experience gravity as our weight, which is to say the attraction between our own mass and the Earth. When a rocket is in space, the vehicle and the astronauts carried by it still feel the pull of the planet’s gravity. No matter where they are, they have some gravitational relationship with objects — from distant planets to faraway stars — however faint it might be. You, too, experience the tug of the entire universe, even if the tug that you notice is from Earth.
Back on the space station, astronauts (and the station itself) are slowly falling toward, or more technically around, the Earth. The astronauts look and feel weightless because they do not experience the Earth pushing back up on them as they would if they took a tumble on terra firma. If you’ve ever been in an elevator that descends quickly, dropping from under your feet, you’ve had a tiny taste of what they experience all the time.
News outlets tend to describe these gravity wells as if they were oversize cosmic vacuums. “Black Hole Sucks Down Star Stuff at 30 Percent Speed of Light,” proclaimed a recent Discover magazine headline. The website Futurism offered a survival guide for those who somehow “get sucked into a black hole.” And then there’s Beavis and Butthead, who warned us that a black hole “sucks up the whole universe, and then it’s like, it grinds it up and sends it all to hell or something.”
In truth, black holes are a bunch of mass crunched together into a tiny volume, creating a huge gravitational field. Where their gravitational field is strongest, not even light, the fastest thing in the universe, can escape. As a result, black holes have long been hard for astronomers to study, since most of our understanding of the universe relies on measuring light.
What we do know is that the huge masses of black holes (anywhere from tens to millions of times the mass of our sun) bend space-time in extreme ways, which is why illustrations often make them look like deep cosmic funnels. If you get close enough to one, you will certainly experience its powerful gravitational force, which is why astronomers see stars orbiting the supermassive black hole at the center of our Milky Way galaxy. But the gravitational tug is just like that of any other object — dependent on mass, and distance — and it’s not special just because it’s caused by a black hole. If I could magically replace our sun with a black hole that had exactly the same mass as our sun, our Earth would keep orbiting exactly where it is now, and similarly, those stars at the center of our galaxy will spend their entire lifetimes happily orbiting, with no danger of getting sucked in. In that sense, black holes are more like sinkholes than vacuums: One sinkhole in Florida isn’t going to destroy the whole Earth, but best not to get too close.
Every child has reached for the yellow crayon or marker when it’s time to draw the sun. This common perception leads to articles like one in Sciworthy that begins, “The yellow sun in our sky provides the light and energy needed to sustain our planet.” Pretty forgivable, given that even astronomers refer to the sun as a “yellow dwarf.” And Superman famously gets his powers from his proximity to “yellow stars.”
Yet to understand the true color of the sun, you have to know a little bit about light itself. Visible light, the kind that human eyes can see, is just a tiny fraction of the energies of light in the universe. Mixed together, all this light appears white — but the colors of the rainbow, from red to violet, are different energies of light that your eyes can see (red is at the lower energy end of the visible spectrum, violet is towards the high energy end). By the time light from the sun hits your eyes (hopefully not directly: please don’t look straight at it!), it has traveled across the solar system and through Earth’s atmospherewhich bends, filters and scatters solar radiation before it makes it to our eyes. Because the higher-energy, bluer light gets scattered more, the light from the sun that reaches our eyes on Earth appears more yellow. But in space, the sun would appear white to us.
As it turns out, when you take the incredibly dynamic surface of the sun, and colorize it in yellows and oranges, it looks a whole lot like fire. Perhaps that’s why we often embrace a fiery vocabulary to describe it, as the band They Might Be Giants did when they referred to the sun as a “nuclear furnace.” Astronomers also speak of the sun “burning ” hydrogen, and Popular Science writes that we’re lucky “it didn’t burn out before we showed up a few hundred thousand years ago.”
In the case of our sun, however, “burning” is a total misnomer. There is no combustion, fed by oxygen, to release the energy stored in the fuel. Stars generate energy through fusion, smashing together atoms deep in their cores like gigantic particle colliders. These fusion reactions take lighter elements, such as hydrogen, and smash them together to build heavier elements (like helium). When hydrogen atoms fuse together, they release energy, which eventually makes it out of the heart of the star to shine into the universe.
To get past Mars, onward to Jupiter and beyond, one must pass through the asteroid belt, a region of space that harbors an especially large number of rocks. That sounds dangerous, at least to some science fans who write into sites like “Ask an Astronomer.” Usually, people’s ideas about the asteroid belt come from scenes in sci-fi movies like “The Empire Strikes Back,” where Han Solo nimbly navigates the Millennium Falcon through a dangerous field strewn with jagged, flying boulders.
In reality, we’ve successfully sent numerous NASA missions to study the outer solar system, no bobbing or weaving required. At the extreme speeds they travel — tens of thousands of miles per hour — spacecraft don’t need to hit a boulder to be annihilated. (Just over two years ago, a window on the International Space Station was seriously damaged by a mere paint chip. ) Navigating the asteroid belt in our solar system, however, is a piece of cake: While it does have a lot of rocks flying around in it compared with other regions of space, those rocks are still incredibly far apart — hundreds of thousands of miles, on average. So, if you’re ever on a road trip with C-3PO, and he claims that “the possibility of successfully navigating an asteroid field is approximately 3,720 to 1 ,” you can tell him to chill out and enjoy the view.