Death by black hole free pdf download

Perry, The Tennessean. Death by Black Hole touches on a lot of amazing scientific concepts that are almost taken by granted by a lot of people today, but it provides a foundation for everything that we do in space or dealing with the cosmos. Tyson is excellent at taking these concepts and putting them in situations that we can understand as non-scientists complete with humor. Leverage in Death ePub by J. Robb Opens in a new browser tab.

Jump in. The thrill of finding out what we do know now, and how what we learn furthers our quest to unlock more and more secrets. The almost-four-minute mismatch between the sidereal and solar days forces the Sun to migrate across the patterns of background stars, creating the impression that the Sun visits the stars in one constellation after another throughout the year.

Once again taking advantage of your timing device, you can try something different with your stick in the ground. Earth tilts on its axis by On only four days a year—corresponding to the top, the bottom, and the middle crossing of the figure eight—is clock time equal to Sun time. As it happens, the days fall on or about April 15 no relation to taxes , June 14 no relation to flags , September 2 no relation to labor , and December 25 no relation to Jesus. Next up, clone yourself and your stick and send your twin due south to a prechosen spot far beyond your horizon.

Agree in advance that you will both measure the length of your stick shadows at the same time on the same day. If the shadows are the same length, you live on a flat or a supergigantic Earth. The astronomer and mathematician Eratosthenes of Cyrene — B. He compared shadow lengths at noon from two Egyptian cities—Syene now called Aswan and Alexandria, which he overestimated to be 5, stadia apart.

Pound your stick into the ground at an angle other than vertical, so that it resembles a typical stick in the mud. Measure the length of the string and then tap the bob to set the pendulum in motion.

Count how many times the bob swings in 60 seconds. On the Moon, with only one-sixth the gravity of Earth, the same pendulum will move much more slowly, executing fewer swings per minute. For the next experiment, find a stick more than 10 yards long and, once again, pound it into the ground at a tilt. Tie a heavy stone to the end of a long, thin string and dangle it from the tip. Now, just like last time, set it in motion.

The long, thin string and the heavy bob will enable the pendulum to swing unencumbered for hours and hours and hours. The most pedagogically useful place to do this experiment is at the geographic North or, equivalently, South Pole. For all other positions on Earth, except along the equator, the plane still turns, but more and more slowly as you move from the Poles toward the equator.

At the equator the plane of the pendulum does not move at all. Today a Foucault pendulum sways in practically every science and technology museum in the world. On the morning of the summer solstice at Stonehenge, for instance, several of the stones in its concentric circles align precisely with sunrise. Certain other stones align with the extreme rising and setting points of the Moon. Begun in about B.

Eighty or so bluestone pillars, each weighing several tons, came from the Preseli Mountains, roughly miles away. The so-called sarsen stones, each weighing as much as 50 tons, came from Marlborough Downs, 20 miles away. Much has been written about the significance of Stonehenge. Historians and casual observers alike are impressed by the astronomical knowledge of these ancient people, as well as by their ability to transport such obdurate materials such long distances.

Some fantasy-prone observers are so impressed that they even credit extraterrestrial intervention at the time of construction. Why the ancient civilizations who built the place did not use the easier, nearby rocks remains a mystery. But the skills and knowledge on display at Stonehenge are not. The major phases of construction took a total of a few hundred years. Perhaps the preplanning took another hundred or so. Furthermore, the astronomy embodied in Stonehenge is not fundamentally deeper than what can be discovered with a stick in the ground.

Perhaps these ancient observatories perennially impress modern people because modern people have no idea how the Sun, Moon, or stars move. To us, a simple rock alignment based on cosmic patterns looks like an Einsteinian feat. But a truly mysterious civilization would be one that made no cultural or architectural reference to the sky at all.

In the cores of stars, beginning at about million degrees Kelvin, but for the Sun, at million degrees, hydrogen nuclei, long denuded of their lone electron, reach high enough speeds to overcome their natural repulsion and collide. Energy is created out of matter as thermonuclear fusion makes a single helium He nucleus out of four hydrogen H nuclei.

Every time a helium nucleus gets created, particles of light called photons get made. And they pack enough punch to be gamma rays, a form of light with the highest energy for which we have a classification. Born moving at the speed of light , miles per second , the gamma-ray photons unwittingly begin their trek out of the Sun. An undisturbed photon will always move in a straight line. But if something gets in its way, the photon will either be scattered or absorbed and re-emitted.

Each fate can result in the photon being cast in a different direction with a different energy. The new travel path after each interaction can be outward, sideways, or even backward. How then does an aimlessly wandering photon ever manage to leave the Sun? A clue lies in what would happen to a fully inebriated person who takes steps in random directions from a street corner lamppost. Curiously, the odds are that the drunkard will not return to the lamppost. If the steps are indeed random, distance from the lamppost will slowly accumulate.

While you cannot predict exactly how far from the lamppost any particular drunk person will be after a selected number of steps, you can reliably predict the average distance if you managed to convince a large number of drunken subjects to randomly walk for you in an experiment. Your data would show that on average, distance from the lamppost increased in proportion to the square root of the total number of paces taken.

For example, if each person took steps in random directions, then the average distance from the lamppost would have been a mere 10 steps. If steps were taken, the average distance would have grown to only 30 steps. The total linear distance traveled would span about 5, lightyears. At the speed of light, a photon would, of course, take 5, years to journey that far. As early as the s, we had some idea that a photon might meet some major resistance getting out of the Sun.

Credit the colorful British astrophysicist Sir Arthur Stanley Eddington for endowing the study of stellar structure with enough of a foundation in physics to offer insight into the problem. In he wrote The Internal Constitution of the Stars, which he published immediately after the new branch of physics called quantum mechanics was discovered, but nearly 12 years before thermonuclear fusion was officially credited as the energy source for the Sun.

We have to call to aid the most recent discoveries of atomic physics to follow the intricacies of the dance…. Try to picture the tumult! Dishevelled atoms tear along at 50 miles a second with only a few tatters left of their elaborate cloaks of electrons torn from them in the scrimmage.

The lost electrons are speeding a hundred times faster to find new resting-places. Look out! A thousand narrow shaves happen to the electron in [one ten-billionth] of a second…. Then…the electron is fairly caught and attached to the atom, and its career of freedom is at an end.

But only for an instant. Barely has the atom arranged the new scalp on its girdle when a quantum of aether waves runs into it. With a great explosion the electron is off again for further adventures. It is more like the jolly crockery-smashing turn of a music-hall. The knockabout comedy of atomic physics is not very considerate towards our aesthetic ideals…. The atoms and electrons for all their hurry never get anywhere; they only change places. The aether waves are the only part of the population which do actually accomplish something; although apparently darting about in all directions without purpose they do in spite of themselves make a slow general progress outwards.

Whole blobs of hot material rise while other blobs of cooler material sink. Unbeknownst to our hardworking photons, their residential blob can swiftly sink tens of thousands of kilometers back into the Sun, thus undoing possibly thousands of years of random walking. Of course the reverse is also true— convection can swiftly bring random-walking photons near the surface, thus enhancing their chances of escape. For every absorption and re-emission, the highenergy gamma-ray photons tend to give birth to multiple lower-energy photons at the expense of their own existence.

Such altruistic acts continue down the spectrum of light from gamma rays to x-rays to ultraviolet to visible and to the infrared. The energy from a single gamma-ray photon is sufficient to beget a thousand x-ray photons, each of which will ultimately beget a thousand visible-light photons. Only one out of every half-billion photons that emerge from the Sun actually heads toward Earth.

The rest of the photons head everywhere else. Only from such a layer can light reach your eye along an unimpeded line of sight, which allows you to assess meaningful solar dimensions. In general, light with longer wavelengths emerges from within deeper layers of the Sun than light of shorter wavelengths.

Not all the energy of our fecund gamma rays became lower-energy photons. A portion of the energy drives the large-scale turbulent convection, which in turn drives pressure waves that ring the Sun the way a clanger rings a bell. The greatest challenges among helioseismologists lie in decomposing the oscillations into their basic parts, and thus deducing the size and structure of the internal features that cause them.

Your vocal sound waves would induce vibrations of the piano strings that shared the same assortment of frequencies that comprise your voice. Their long-anticipated results supported most current notions of stellar structure. Yes, some discoveries are great simply because they confirm what you had suspected all along. Heroic adventures through the Sun are best taken by photons and not by any other form of energy or matter. Aside from these setbacks, I imagine one could easily sell tickets for such a voyage.

For me, though, I am content just knowing the story. When I sunbathe, I do it with full respect for the journey made by all photons that hit my body, no matter where on my anatomy they strike. Of the eight objects in our solar system that are indisputably planets, five are readily visible to the unaided eye and were known to the ancients, as well as observant troglodytes.

Each of the five—Mercury, Venus, Mars, Jupiter, and Saturn—was endowed with the personality of the god for which it was named. For example, Mercury, which moves the fastest against the background stars, was named for the Roman messenger god—the fellow usually depicted with small and aerodynamically useless wings on his heels or his hat. Earth, of course, is also visible to the unaided eye. Just look down. But terra firma was not identified as one of the gang of planets until after , when Nicolaus Copernicus advanced his Sun-centered model of the universe.

To the telescopically challenged, the planets were, and are, just points of light that happen to move across the sky. Not until the seventeenth century, with the proliferation of telescopes, did astronomers discover that planets were orbs. Not until the twentieth century were the planets scrutinized at close range with space probes. And not until later in the twenty-first century will people be likely to visit them.

Humanity had its first telescopic encounter with the celestial wanderers during the winter of — After merely hearing of the Dutch invention, Galileo Galilei manufactured an excellent telescope of his own design, through which he saw the planets as orbs, perhaps even other worlds. The simplest way to explain the phases of Venus, as well as other features of its motion on the sky, was to assert that the planets revolve around the Sun, not Earth.

Galileo discovered with his telescope a contradiction to the dogma that Earth occupied the central position in the cosmos—the spot around which all objects revolve. Nobody imagined there could be more than six. Not even the English astronomer Sir William Herschel, who discovered a seventh in Actually, the credit for the first recorded sighting of the seventh planet goes to the English astronomer John Flamsteed, the first British Astronomer Royal. He assumed it was just another star in the sky, and named it 34 Tauri.

Comets, after all, were known to move and to be discoverable. If the astronomical community had respected these wishes, the roster of our solar system would now include Mercury, Venus, Earth, Mars, Jupiter, Saturn, and George. Still, our knowledge of the planets was meager, and where ignorance lurks, so too do the frontiers of discovery and imagination. Like so many investigators around the world, Lowell picked up on the late-nineteenth-century proposition by the Italian astronomer Giovanni Schiaparelli that linear markings visible on the Martian surface were canali.

The story was appealing, and it helped generate plenty of vivid writing. Lowell maintained that Venus sported a network of massive, mostly radial spokes more canali emanating from a central hub. The spokes he saw remained a puzzle. In fact nobody could ever confirm what he saw on either Mars or Venus. And the episode is today remembered as one where the urge to believe undermined the need to obtain accurate and responsible data. And curiously, it was not until the twenty-first century that anybody could explain what was going on at the Lowell Observatory.

An optometrist from Saint Paul, Minnesota, named Sherman Schultz wrote a letter in response to an article in the July issue of Sky and Telescope magazine. Alas, Lowell fared only slightly better with his search for Planet X, a planet thought to lie beyond Neptune.

Planet X does not exist, as the astronomer E. Myles Standish Jr. Pluto is just too small, too lightweight, too icy, too eccentric in its orbit, too misbehaved. And by the way, we say the same about the recent high-profile contenders including the three or four objects discovered beyond Pluto that rival Pluto in size and in table manners. Come the s, radio-wave observations and better photography revealed fascinating facts about the planets.

By the s, people and robots had left Earth to take family photos of the planets. And with each new fact and photograph the curtain of ignorance lifted a bit higher. Venus, named after the goddess of beauty and love, turns out to have a thick, almost opaque atmosphere, made up mostly of carbon dioxide, bearing down at nearly times the sea level pressure on Earth.

Worse yet, the surface air temperature nears degrees Fahrenheit. On Venus you could cook a inch pepperoni pizza in seven seconds, just by holding it out to the air. Yes, I did the math.

Such extreme conditions pose great challenges to space exploration, because practically anything you can imagine sending to Venus will, within a moment or two, get crushed, melted, or vaporized. It suffers from a runaway greenhouse effect, induced by the carbon dioxide in its atmosphere, which traps infrared energy. This same terrain then reradiates the visible light as infrared, which builds and builds in the air, eventually creating—and now sustaining—a remarkable pizza oven.

By the way, were we to find life-forms on Venus, we would probably call them Venutians, just as people from Mars would be Martians. Unfortunately, medical doctors reached that word before astronomers did. Venereal disease long predates astronomy, which itself stands as only the second oldest profession. The rest of the solar system continues to become more familiar by the day.

The first spacecraft to fly past Mars was Mariner 4, in , and it sent back the first-ever close-ups of the Red Planet. Nobody knew it had mountains, or a canyon system vastly wider, deeper, and longer than the Grand Canyon. Nobody knew it had volcanoes vastly bigger than the largest volcano on Earth—Mauna Kea in Hawaii—even when you measure its height from the bottom of the ocean. Nor is there any shortage of evidence that liquid water once flowed on the Martian surface: the planet has dry meandering riverbeds as long and wide as the Amazon, webs of dry tributaries, dry river deltas, and dry floodplains.

The Mars exploration rovers, inching their way across the dusty rock-strewn surface, confirmed the presence of surface minerals that form only in the presence of water. Yes, signs of water everywhere, but not a drop to drink. Something bad happened on both Mars and Venus.

Could something bad happen on Earth too? Our species currently turns row upon row of environmental knobs, without much regard to long-term consequences.

Who even knew to ask these questions of Earth before the study of Mars and Venus, our nearest neighbors in space, forced us to look back on ourselves? Both passed by Jupiter two years later, executing a grand tour along the way.

How do you get a spacecraft to go farther than its energy supply will carry it? You aim it, fire the rockets, and then just let it coast to its destination, falling along the streams of gravitational forces set up by everything in the solar system.

And because astrophysicists map trajectories with precision, probes can gain energy from multiple slingshot-style maneuvers that rob orbital energy from the planets they visit. Orbital dynamicists have gotten so good at these gravity assists that they make pool sharks jealous. But it was the twin spacecraft Voyager 1 and 2— launched in and equipped with a suite of scientific experiments and imagers—that turned the outer planets into icons.

Voyager 1 and 2 brought the solar system into the living rooms of an entire generation of world citizens. One of the windfalls of those journeys was the revelation that the moons of the outer planets are just as different from one another, and just as fascinating, as the planets themselves. Hence those planetary satellites graduated from boring points of light to worlds worthy of our attention and affection.

Other complex NASA missions are now being planned that will do the same for Jupiter, allowing a sustained study of the planet and its plus moons. For these and related blasphemous transgressions, the Catholic Church had Bruno burned at the stake. Yet Bruno was neither the first nor the last person to posit some version of those ideas.

His predecessors range from the fifth-century B. Greek philosopher Democritus to the fifteenth-century cardinal Nicholas of Cusa. Bruno was just unlucky to be born at a time when you could get executed for such thoughts. No doubt that life as we know it requires liquid water, but everyone had just assumed that life also required starlight as its ultimate source of energy. Io is the most volcanically active place in the solar system, belching sulfurous gases into its atmosphere and spilling lava left and right.

Europa almost surely has a deep billion-year-old ocean of liquid water beneath its icy crust. Even right here on Earth, new categories of organisms, collectively called extremophiles, thrive in conditions inimical to human beings.

The concept of a habitable zone incorporated an initial bias that room temperature is just right for life.

But some organisms just love several-hundred-degree hot tubs and find room temperature downright hostile. To them, we are the extremophiles. Many places on Earth, previously presumed to be unlivable, such creatures call home: the bottom of Death Valley, the mouths of hot vents at the bottom of the ocean, and nuclear waste sites, to name just a few. Armed with the knowledge that life can appear in places vastly more diverse than previously imagined, astrobiologists have broadened the earlier, and more restricted, concept of a habitable zone.

Today we know that such a zone must encompass the newfound hardiness of microbial life as well as the range of energy sources that can sustain it. And, just as Bruno and others had suspected, the roster of confirmed exosolar planets continues to grow by leaps and bounds. That number has now risen past —all discovered in the past decade or so. Once again we resurrect the idea that life might be everywhere, just as our ancestors had imagined.

But today, we do so without risk of being immolated, and with the newfound knowledge that life is hardy and that the habitable zone may be as large as the universe itself. It included the Sun, the stars, the planets, a handful of planetary moons, and the comets. During the next two centuries, the family album of the solar system became crammed with the data, photographs, and life histories of asteroids, as astronomers located vast numbers of these vagabonds, identified their home turf, assessed their ingredients, estimated their sizes, mapped their shapes, calculated their orbits, and crash-landed probes on them.

Some investigators have also suggested that the asteroids are kinfolk to comets and even to planetary moons. And at this very moment, some astrophysicists and engineers are plotting methods to deflect any big ones that may be planning an uninvited visit. One curious fact about the planets is captured in a fairly simple mathematical rule proposed in by a Prussian astronomer named Johann Daniel Titius.

Their handydandy formula yielded pretty good estimates for the distances between the planets and the Sun, at least for the ones known at the time: Mercury, Venus, Earth, Mars, Jupiter, and Saturn.

In , widespread knowledge of the Titius-Bode law actually helped lead to the discovery of Neptune, the eighth planet from the Sun. So either the law is just a coincidence, or it embodies some fundamental fact about how solar systems form. Problem number 1: You have to cheat a little to get the right distance for Mercury, by inserting a zero where the formula calls for 1.

Problem number 2: Neptune, the eighth planet, turns out to be much farther out than the formula predicts, orbiting more or less where a ninth planet should be. Problem no. The law would also put a planet orbiting in the space between Mars and Jupiter—at about 2.

Subsequently it disappeared behind the glare of the Sun, but exactly one year later, with the help of brilliant computations by the German mathematician Carl Friedrich Gauss, the new object was rediscovered in a different part of the sky.

Everybody was excited: a triumph of mathematics and a triumph of telescopes had led to the discovery of a new planet. Within a few more years three more teeny planets—Pallas, Juno, and Vesta—were discovered in the same zone.

Further observations revealed a proliferation of asteroids, and by the end of the nineteenth century, of them had been discovered in and around the swath of celestial real estate at 2. And because the swath turned out to be a relatively flat band and did not scatter around the Sun in every direction, like bees around a hive, the zone became known as the asteroid belt.

By now, many tens of thousands of asteroids have been catalogued, with hundreds more discovered every year. Altogether, by some estimates, more than a million measure a half-mile across and up. So asteroids can now be named after actors, painters, philosophers, and playwrights; cities, countries, dinosaurs, flowers, seasons, and all manner of miscellany. Even regular people have asteroids named after them.

David H. Levy, a Canadian-born amateur astronomer who is the patron saint of comet hunters but has discovered plenty of asteroids as well, was kind enough to pull an asteroid from his stash and name it after me, Tyson. The others are much smaller, craggy fragments shaped like doggy bones or Idaho potatoes. Curiously, Ceres alone accounts for about a quarter of the total asteroidal mass. So the prediction from Titius-Bode, that a redblooded planet lurks at 2.

Asteroids are usually described as being formed of material left over from the earliest days of the solar system—material that never got incorporated into a planet. But that explanation is incomplete at best and does not account for the fact that some asteroids are pure metal. The planets coalesced from a cloud of gas and dust enriched by the scattered remains of element-rich exploding stars. The collapsing cloud forms a protoplanet— a solid blob that gets hot as it accretes more and more material.

Two things happen with the larger protoplanets. One, the blob tends to take on the shape of a sphere. Two, its inner heat keeps the protoplanet molten long enough for the heavy stuff—primarily iron, with some nickel and a splash of such metals as cobalt, gold, and uranium mixed in —to sink to the center of the growing mass.

Meanwhile, the much more common, light stuff—hydrogen, carbon, oxygen, and silicon—floats upward toward the surface. Once it has cooled, if such a planet is then destroyed —say, by smashing into one of its fellow planets—the fragments of both will continue orbiting the Sun in more or less the same trajectories that the original, intact objects had. Most of those fragments will be rocky, because they come from the thick, outer, rocky layers of the two differentiated objects, and a small fraction will be purely metallic.

To concentrate the iron atoms, a fluid body must first have differentiated. Or how do they know anything at all? Does Harriet reflect or absorb infrared?

What about visible light? Different materials absorb and reflect the various bands of light differently. And from the material, you can know how much light gets reflected. This method of spectral analysis led initially to a simplified three-way classification scheme, with carbon-rich BUT HOW DO C-type asteroids, silicate-rich S-type asteroids, and metalrich M-type asteroids.

Curiously, some measurements of the sizes of asteroids and their masses yielded densities that were less than that of rock. What else could be mixed in? Ice, perhaps? Not likely.

The first bit of observational support for that hypothesis appeared in images of the mile-long asteroid Ida, photographed by the space probe Galileo during its flyby on August 28, Dubbed Dactyl, it was the first satellite ever seen orbiting an asteroid. Are satellites a rare thing? If an asteroid can have a satellite orbiting it, could it have two or ten or a hundred? In other words, could some asteroids turn out to be heaps of rocks? The answer is a resounding yes. One of the most extreme examples of the type may be Psyche, which measures about miles in overall diameter and is reflective, suggesting its surface is metallic.

From estimates of its overall density, however, its interior may well be more than 70 percent empty space. Comets are the snowballs of the cosmos. In fact, they may simply be asteroids with a cloak of ice that never fully evaporated. Before Newton published his Principia in , in which he laid out the universal laws of gravitation, no one had any idea that comets lived and traveled among the planets, making their rounds in and out of the solar system in highly elongated orbits.

Icy fragments that formed in the far reaches of the solar system, whether in the Kuiper Belt or beyond, remain shrouded in ice and, if found on a characteristic elongated path toward the Sun, will show a rarefied but highly visible trail of water vapor and other volatile gases when it swings inside the orbit of Jupiter. Eventually, after enough visits to the inner solar system could be hundreds or even thousands such a comet can lose all its ice, ending up as bare rock.

Then there are the meteorites, flying cosmic fragments that land on Earth. To the planetary geologists who studied the growing number of known asteroids, it became clear that not all orbits hailed from the main asteroid belt. As Hollywood loves to remind us, someday an asteroid or comet might collide with Earth, but that likelihood was not recognized as real until , when the astrogeologist Eugene M. Shoemaker demonstrated conclusively that the vast 50,year-old Barringer Meteorite Crater near Winslow, Arizona, could have resulted only from a meteorite impact, and not from volcanism, or some other Earth-based geologic forces.

A gravitational balancing act between Jupiter and the Sun has collected families of asteroids 60 degrees ahead of Jupiter in its solar orbit, and 60 degrees behind it, each making an equilateral triangle with Jupiter and the Sun. If you do the geometry, it places the asteroids 5. As we will see in the next chapter, these regions act like tractor beams, holding fast to asteroids that drift their way.

Jupiter also deflects plenty of comets that head toward Earth. Most comets live in the Kuiper Belt, beginning with and extending far beyond the orbit of Pluto. But any comet daring enough to pass close to Jupiter will get flung into a new direction. Were it not for Jupiter as guardian of the moat, Earth would have been pummeled by comets far more often than it has.

In fact, the Oort Cloud, which is a vast population of comets in the extreme outer solar system, named for Jan Oort, the Danish astronomer who first proposed its existence, is widely thought to be composed of Kuiper Belt comets that Jupiter flung hither and yon. Indeed, the orbits of Oort Cloud comets extend halfway to the nearest stars. What about the planetary moons? Some look like captured asteroids, such as Phobos and Deimos, the small, dim, potato-shaped moons of Mars.

But Jupiter owns several icy moons. Should those be classified as comets? Meanwhile, both of them are icy. So perhaps they should be regarded instead as a double comet. The first to do so was the car-sized robotic U. It touched down at just four miles an hour and, instruments intact, unexpectedly continued to send back data for two weeks after landing, enabling planetary geologists to say with some confidence that mile-long Eros is an undifferentiated, consolidated object rather than a rubble pile.

The goal of the mission was, quite simply, to find out what kinds of space dust are out there and to collect the particles without damaging them. When a particle slams in at hypersonic speeds, the particle bores its way in and gradually comes to a stop, intact. The European Space Agency is also out there exploring comets and asteroids.

The Rosetta spacecraft, on a year mission, will explore a single comet for two years, amassing more information at close range than ever before, and will then move on to take in a couple of asteroids in the main belt.

Each of these vagabond encounters seeks to gather highly specific information that may tell us about the formation and evolution of the solar system, about the kinds of objects that populate it, about the possibility that organic molecules were transferred to Earth during impacts, or about the size, shape, and solidity of near-earth objects. And, as always, deep understanding comes not from how well you describe an object, but from how that object connects with the larger body of acquired knowledge and its moving frontier.

For the solar system, that moving frontier is the search for other solar systems. What scientists want next is a thorough comparison of what we and exosolar planets and vagabonds look like. Only in this way will we know whether our home life is normal or whether we live in a dysfunctional solar family. This achievement remains one of the most remarkable, yet unheralded firsts of the twentieth century. When that moment arrived, the astronauts fired the third and final stage of their mighty Saturn V rocket, rapidly thrusting the command module and its three occupants up to a speed of nearly seven miles per second.

The engines were no longer necessary after the third stage fired, except for any midcourse tuning the trajectory might require to ensure the astronauts did not miss the Moon entirely. When the command module drifted across that point in space, its speed increased once again as it accelerated toward the Moon.

If gravity were the only force to be reckoned, then this spot would be the only place in the Earth-Moon system where the opposing forces canceled each other out. When objects move in circles of any size and at any speed, they create a new force that pushes outward, away from the center of rotation. In a classic example of these nauseainducing rides, you stand along the edge of a large circular platter, with your back against a perimeter wall.

As the contraption spins up, rotating faster and faster, you feel a stronger and stronger force pinning you against the wall. At top speeds, you can barely move against the force. When I rode one of these as a kid, the force was so great that I could barely move my fingers, they being stuck to the wall along with the rest of me. If you actually got sick on such a ride, and turned your head to the side, the vomit would fly off at a tangent.

Or it might get stuck to the wall. But you can calculate with them as though they are. When you do, as did the brilliant eighteenth-century French mathematician Joseph-Louis Lagrange — , you discover spots in the rotating Earth-Moon system where the gravity of Earth, the gravity of the Moon, and the centrifugal forces of the rotating system balance. These special locations are known as the points of Lagrange.

And there are five of them. The first point of Lagrange affectionately called L1 falls between Earth and the Moon, slightly closer to Earth than the point of pure gravitational balance. Any object placed there can orbit the Earth-Moon center of gravity with the same monthly period as the Moon and will appear to be locked in place along the Earth-Moon line. Although all forces cancel there, this first Lagrangian point is a precarious equilibrium.

If the object drifts sideways in any direction, the combined effect of the three forces will return it to its former position. The second and third Lagrangian points L2 and L3 also lie on the Earth-Moon line, but this time L2 lies far beyond the far side of the Moon, while L3 lies far beyond Earth in the opposite direction.

And once again, an object placed in either spot can orbit the Earth-Moon center of gravity with the same monthly period as the Moon. The gravitational hilltops represented by L2 and L3 are much broader than the one represented at L1. So if you find yourself drifting down to Earth or the Moon, only a tiny investment in fuel will bring you right back to where you were. Web icon An illustration of a computer application window Wayback Machine Texts icon An illustration of an open book. Books Video icon An illustration of two cells of a film strip.

Video Audio icon An illustration of an audio speaker. Audio Software icon An illustration of a 3. Software Images icon An illustration of two photographs. Images Donate icon An illustration of a heart shape Donate Ellipses icon An illustration of text ellipses.