Someone who “missed” the late part of the twentieth century, perhaps by being in a coma or a deep sleep, or by being marooned on a desert island, would have many adjustments to make upon rejoining civilization. The largest would probably be the galloping progress in computers and telecommunications and information technology. But if their attention turned to astronomy, they would also be amazed by what had been learned in the interim. In the last third of the century, Mars turned from a pale red disk as seen through a telescope to a planet with ancient lake beds and subterranean...

Sometimes the dream is a nightmare. Mars has always had an ominous mien in myth and culture. Ancient civilizations regarded the planet as a malevolent agent of war and apocalypse. Similar myths emerged around the world.¹ In late Babylonian texts, Mars is identified with Nergal, the fiery god of destruction and war. To the Greeks, Mars was Ares, one of Twelve Olympians and the son of Zeus and Hera. His attendants on the battlefield were Deimos and Phobos, terror and fear, and his sister and companion was Eris, the goddess of discord.² Ares was an important but an unlikeable character....

The essay is short and very simple; the words are almost heartbreaking: “I used to live in an orphanage. It was dark and cold and lonely. At night, I looked up at the sparkly sky and felt better. I dreamed I could fly there. In America, I can make all my dreams come true. . . . Thank you for the Spirit and the Opportunity.”¹ Sofi Collis was abandoned at birth into a Siberian orphanage and brought by her adoptive parents to live in Scottsdale, Arizona. In 2003, at age nine, she was writing in response to a call from...

There’s a NASA website where you can follow the two most distant human artifacts as they sail into the void of space. The real-time odometers for the Voyager 1 and Voyager 2 spacecraft flick silently upward. Single kilometers are a blur; even the tens of kilometers digit changes too fast to follow, while the hundreds of kilometers digit ratchets up by one every few seconds. These large and rapidly growing numbers are mesmerizing in the same way as counters of the national debt or the world’s population; numbers this large are difficult to fathom. By late-2012, Voyager 1 was 18.4...

“It is a drama as ancient as the sun, as unflinching as time . . . a never-ending whirl of celestial movements, scripted and precise, in a silent show of cosmic force, played out in light and shadow. It is a drama called equinox,” writes Cassini Imaging Team Leader Carolyn Porco in her “Captain’s Log,” an online diary of the Cassini spacecraft’s observations of the ringed world of Saturn and its moons. It takes approximately thirty years for Saturn to orbit the Sun, so the planet only experiences an equinox, when the Sun shines equally on its northern and southern...

The story of life in the universe is a story of stars. As the first clouds of gas formed stars in the infant universe, more than 13 billion years ago, the universe contained only hydrogen, helium, and a few other trace light elements. The nuclei of these light elements were forged in the intense heat a few minutes after the big bang, when the entire universe was as hot as the core of the Sun is now. As the universe rapidly expanded, radiation eased its grip and a scant half million years after the big bang, it had cooled enough...

Imagine you woke up one morning and your planet had been engulfed by the atmosphere of a star. High-energy particles slam into the atmosphere, creating shimmering auroras. Sunspots flicker, each one releasing more energy than the largest atomic bomb. Great loops of hot gas uncoil from the star’s surface, extending millions of miles. Each whip crack of activity causes mayhem on orbiting satellites, frying their circuit boards and wreaking havoc on their guidance systems. Your planet is assailed by high-energy particles traveling at nearly the speed of light. Looking at the star, its emission doesn’t change detectably from day to...

A 1939 biography of Albert Einstein offers a poignant example of the perspective that helped shape the famous scientist’s relativistic view of Earth in space: “The world is moving along rapidly in space: your office in the morning will not be where it was when you left it at the close of business. It will never be in the same place in space again!”¹ Indeed, the Sun plunges daily some 12.5 million miles through the empty wastes of space, never to return to its former location. The Earth orbits the Sun at roughly 67,100 miles per hour even as the...

Space is mostly empty, but a thin gruel of gas and dust that occupies regions between stars dims and reddens light.¹ Thousand-trillion-mile wide clouds containing gas and microscopic dust grains absorb and attenuate visible light and reradiate it at infrared wavelengths. NASA’s Spitzer Space Telescope has the remarkable ability to see through interstellar dust and has allowed us to look into the vast clouds in which stars are born, like those of the Orion Nebula, our nearest star-forming region. Spitzer can also peer into the dark, dust strewn plane of our Milky Way galaxy that previously had been nearly impossible...

When we dream of other worlds, our dreams may be vivid and real and colorful, but they’re subject to the limitations of our senses. To visualize something, even if in our mind’s eye, we use the visual sense. For most of the history of astronomy we learned about the universe exclusively through visible light. Tens of thousands of years of naked-eye observations were followed by the first night time use of the telescope by Galileo in 1610, followed by a steady march of successively larger telescopes, culminating with the 8–11 meter behemoths of the present day, with dreams of...

Above all scientific projects, the Hubble Space Telescope encapsulates and recapitulates the human yearning to explore distant worlds, and understand our origins and place in the universe. Its light grasp is 10 billion times better than Galileo’s best spyglass, and many innovations were needed for it to be realized: complex yet reliable instruments, the ability for astronauts to service the telescope,¹ and the infrastructure to support the projects of thousands of scientists from around the world. The facility and its supporters experienced failure and heartache as well as eventual success and vindication.

Hubble’s legacy has touched every area of astronomy,...

Awareness of the size and age of the universe is hard-won knowledge that has taxed scientists for the past 2,500 years. To ancient cultures, the sky was a proximate canopy that circled overhead, and there was no sense of the vast distance to the stars, let alone the idea that something might lie beyond those pinpoints of light. The ancient Greeks were the first civilization to spawn a class of philosopher-scientists, who applied logic and mathematics to their observations of the sky.

Cosmology has its root in the Greek idea of “cosmos,” or an orderly and harmonious system. In the...

At the beginning of this book we encountered the Greek philosophers who let their imaginations roam beyond the visible, everyday world. One was Democritus, who was forty years younger than Anaxagoras; apparently, they knew each other. Democritus was known as the “laughing philosopher” for his habit of seeing the lighter side of life and mocking human frailties. He developed an original idea of Leucippus into the atomic theory. According to Democritus, the physical world was made of microscopic, indivisible entities called atoms.² The atoms were in constant motion and they could take up an infinite number of different arrangements; sensory...