Read "Death by Black Hole: And Other Cosmic Quandaries" by Neil deGrasse Tyson available from Rakuten Kobo. Sign up today and get $5 off your first. Topics Science, universe, cosmos, everything, knowledge, wisdom, space, astronomy, black hole, star, sun, planet, Earth, big bang, Theory. Loyal readers of the monthly "Universe" essays in Natural History magazine have long recognized Neil deGrasse Tyson's talent for guiding them through the mysteries of the cosmos with stunning clarity and almost childlike enthusiasm. Here, Tyson compiles his favorite essays across.
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Death by Black Hole? explores a myriad of cosmic topics, from what it would be like to be inside a black hole to the movie industry's feeble. Praise for DEATH BY BLACK HOLE “Tyson proves that no topic is too big or small for his scrutiny. [He] tackles an impressive range of subjects with great . Editorial Reviews. From Publishers Weekly. What would it feel like if your spaceship were to eBook features: Highlight, take notes, and search in the book.
That effect would not be measured until , by the German astronomer Friedrich Wilhelm Bessel. Fearful that this heretical work would freak out the establishment, Andreas Osiander, a Protestant theologian who oversaw the late stages of the printing, supplied an unauthorized and unsigned preface to the work, in which he pleads: I have no doubt that certain learned men, now that the novelty of the hypothesis in this work has been widely reported—for it establishes that the Earth moves and indeed that the Sun is motionless in the middle of the universe—are extremely shocked….
I can well appreciate, Holy Father, that as soon as certain people realize that in these books which I have written about the Revolutions of the spheres of the universe I attribute certain motions to the globe of the Earth, they will at once clamor for me to be hooted off the stage with such an opinion. Once Earth no longer occupied a unique place in the cosmos, the Copernican revolution, based on the principle that we are not special, had officially begun.
At the center of the universe? No way. Nobody was going to fall for that one again; it would violate the freshly minted Copernican principle. If the solar system were in the center of the universe, then no matter where we looked on the sky we would see approximately the same number of stars. But if the solar system were off to the side somewhere, we would presumably see a great concentration of stars in one direction—the direction of the center of the universe.
Slightly more than a century later, the Dutch astronomer Jacobus Cornelius Kapteyn—using the best available methods for calculating distance—sought to verify once and for all the location of the solar system in the galaxy.
When seen through a telescope, the band of light called the Milky Way resolves into dense concentrations of stars. Careful tallies of their positions and distances yield similar numbers of stars in every direction along the band itself.
Above and below it, the concentration of stars drops symmetrically. No matter which way you look on the sky, the numbers come out about the same as they do in the opposite direction, degrees away. Kapteyn devoted some 20 years to preparing his sky map, which, sure enough, showed the solar system lying within the central 1 percent of the universe. But the cosmic cruelty continued. Little did anybody know at the time, especially not Kapteyn, that most sight lines to the Milky Way do not pass all the way through to the end of the universe.
The Milky Way is rich in large clouds of gas and dust that absorb the light emitted by objects behind them. When we look in the direction of the Milky Way, more than 99 percent of all stars that should be visible to us are blocked from view by gas clouds within the Milky Way itself.
By —but before the light-absorption problem was well understood—Harlow Shapley, who was to become director of the Harvard College Observatory, studied the spatial layout of globular clusters in the Milky Way. Globular clusters are tight concentrations of as many as a million stars and are seen easily in regions above and below the Milky Way, where the least amount of light is absorbed. Shapley reasoned that these titanic clusters should enable him to pinpoint the center of the universe—a spot that, after all, would surely have the highest concentration of mass and the strongest gravity.
Where was this special place he found? Sixty thousand light-years away, in roughly the same direction as—but far beyond—the stars that trace the constellation Sagittarius. It coincides with what was later found to be the most powerful source of radio waves in the night sky radio waves are unattenuated by intervening gas and dust.
Once again the Copernican principle had triumphed. The solar system was not in the center of the known universe but far out in the suburbs. For sensitive egos, that could still be okay. Surely the vast system of stars and nebulae to which we belong comprised the entire universe.
Surely we were where the action was. Most of the nebulae in the night sky are like island universes, as presciently proposed in the eighteenth century by several people, including the Swedish philosopher Emanuel Swedenborg, the English astronomer Thomas Wright, and the German philosopher Immanuel Kant.
In An Original Theory of the Universe , for instance, Wright speculates on the infinity of space, filled with stellar systems akin to our own Milky Way: We may conclude…that as the visible Creation is supposed to be full of sidereal Systems and planetary Worlds,…the endless Immensity is an unlimited Plenum of Creations not unlike the known Universe…. The rest of the nebulae turn out to be relatively small, nearby clouds of gas, found mostly within the Milky Way band.
That the Milky Way is just one of multitudes of galaxies that comprise the universe was among the most important discoveries in the history of science, even if it made us feel small again. The offending evidence came in the form of a photographic plate taken on the night of October 5, The offending cosmic object was the Andromeda nebula, one of the largest on the night sky.
Hubble discovered a highly luminous kind of star within Andromeda that was already familiar to astronomers from surveys of stars much closer to home. The distances to the nearby stars were known, and their brightness varies only with their distance. By applying the inverse-square law for the brightness of starlight, Hubble derived a distance to the star in Andromeda, placing the nebula far beyond any known star within our own stellar system.
Andromeda was actually an entire galaxy, whose fuzz could be resolved into billions of stars, all situated more than 2 million light-years away. Not only were we not in the center of things, but overnight our entire Milky Way galaxy, the last measure of our self-worth, shrank to an insignificant smudge in a multibillion-smudge universe that was vastly larger than anyone had previously imagined.
Just six years after Hubble demoted us, he pooled all the available data on the motions of galaxies. Turns out that nearly all of them recede from the Milky Way, at velocities directly proportional to their distances from us. Finally we were in the middle of something big: As a matter of fact, a theory of the universe had been waiting in the wings since , when Albert Einstein published his paper on general relativity—the modern theory of gravity.
When applied to the cosmos, general relativity allows the space of the universe to expand, carrying its constituent galaxies along for the ride. A remarkable consequence of this new reality is that the universe looks to all observers in every galaxy as though it expands around them. But surely there is only one cosmos—the one where we live in happy delusion. At the moment, cosmologists have no evidence for more than one universe. But if you extend several well-tested laws of physics to their extremes or beyond , you can describe the small, dense, hot birth of the universe as a seething foam of tangled space-time that is prone to quantum fluctuations, any one of which could spawn an entire universe of its own.
The idea relegates us to an embarrassingly smaller part of the whole than we ever imagined. Hubble summarized the issues in his work Realm of the Nebulae, but these words could apply at all stages of our endarkenment: Thus the explorations of space end on a note of uncertainty…. We know our immediate neighborhood rather intimately.
With increasing distance our knowledge fades, and fades rapidly. Eventually, we reach the dim boundary—the utmost limits of our telescopes. There, we measure shadows, and we search among ghostly errors of measurement for landmarks that are scarcely more substantial.
That humans are emotionally fragile, perennially gullible, hopelessly ignorant masters of an insignificantly small speck in the cosmos. Have a nice day. The old story about the blind men and the elephant makes the same point: One of the challenges of scientific inquiry is knowing when to step back—and how far back to step—and when to move in close.
In some contexts, approximation brings clarity; in others it leads to oversimplification. A raft of complications sometimes points to true complexity and sometimes just clutters up the picture. As we will see in Section 3, a single particle cannot have a temperature, because the very concept of temperature addresses the average motion of all the molecules in the group.
In biochemistry, by contrast, you understand next to nothing unless you pay attention to how one molecule interacts with another. So, when does a measurement, an observation, or simply a map have the right amount of detail? But the answer is deeper than anyone had imagined.
Explorers and cartographers have been mapping coastlines for centuries. Unwind the string along the perimeter of Britain, from Dunnet Head down to Lizard Point, making sure you go into all the bays and headlands. Wanting to spot-check your work, you get hold of a IN more detailed ordnance survey map, scaled at, say, 2. You find that the survey map shows the coastline to be longer than the atlas did. So which measurement is correct? Yet you could have chosen a map that has even more detail—one that shows every boulder that sits at the base of every cliff.
Where does all this end? Each time you measure it, the coastline gets longer and longer. If you take into account the boundaries of molecules, atoms, subatomic particles, will the coastline prove to be infinitely long? Not exactly. Perhaps the concept of one-dimensional length is simply illsuited for convoluted coastlines.
The ordinary concepts of dimension, Mandelbrot argued, are just too simplistic to characterize the complexity of coastlines. Broccoli, ferns, and snowflakes are good examples from the natural world, but only certain computer-generated, indefinitely repeating structures can produce the ideal fractal, in which the shape of the macro object is made up of smaller versions of the same shape or pattern, which are in turn formed from even more miniature versions of the very same thing, and so on indefinitely.
As you descend into a pure fractal, however, even though its components multiply, no new information comes your way—because the pattern continues to look the same. By contrast, if you look deeper and deeper into the human body, you eventually encounter a cell, an enormously complex structure endowed with different attributes and operating under different rules than the ones that hold sway at the macro levels of the body.
Crossing the boundary into the cell reveals a new universe of information. One of the earliest representations of the world, preserved on a 2,year-old Babylonian clay tablet, depicts it as a disk encircled by oceans. Fact is, when you stand in the middle of a broad plain the valley of the Tigris and Euphrates rivers, for instance and check out the view in every direction, Earth does look like a flat disk.
Noticing a few problems with the concept of a flat Earth, the ancient Greeks—including such thinkers as Pythagoras and Herodotus—pondered the possibility that Earth might be a sphere. In the fourth century B. One of them was based on lunar eclipses.
Every now and then, the Moon, as it orbits Earth, intercepts the cone-shaped shadow that Earth casts in space. For that to be true, Earth had to be a sphere, because only spheres cast circular shadows via all light sources, from all angles, and at all times.
If Earth were a flat disk, the shadow would sometimes be oval. Only when Earth was face-on to the Sun would its shadow cast a circle. Given the strength of that one argument, you might think cartographers would have made a spherical model of Earth within the next few centuries.
But no. The earliest known terrestrial globe would wait until —92, on the eve of the European ocean voyages of discovery and colonization. But the devil, as always, lurks in the details. The degree was slightly longer at the Arctic Circle, which could only be true if Earth were a bit flattened. Newton was right. The faster a planet spins, the greater we expect its equatorial bulge to be. A single day on fast-spinning Jupiter, the most massive planet in the solar system, lasts 10 Earth-hours; Jupiter is 7 percent wider at its equator than at its poles.
And if you really want to do things right, climb Mount Chimborazo in central Ecuador, close to the equator. In the small Earth orbiter Vanguard 1 sent back the news that the equatorial bulge south of the equator was slightly bulgier than the bulge north of the equator.
Not only that, sea level at the South Pole turned out to be a tad closer to the center of Earth than sea level at the North Pole. Next up is the disconcerting fact that Earth is not rigid. Its surface rises and falls daily as the oceans slosh in and out of the continental shelves, pulled by the Moon and, to a lesser extent, by the Sun.
Tidal forces distort the waters of the world, making their surface oval. A well-known phenomenon. But tidal forces stretch the solid earth as well, and so the equatorial radius fluctuates daily and monthly, in tandem with the oceanic tides and the phases of the Moon.
Will the refinements never end? Perhaps not. Fast forward to Thus, the geoid embodies the truly horizontal, fully accounting for all the variations in Earth shape and subsurface density of matter.
Carpenters, land surveyors, and aqueduct engineers will have no choice but to obey. Orbits are multidimensional, unfolding in both space and time. Aristotle advanced the idea that Earth, the Sun, and the stars were locked in place, attached to crystalline spheres.
It was the spheres that rotated, and their orbits traced—what else? To Aristotle and nearly all the ancients, Earth lay at the center of all this activity. Nicolaus Copernicus disagreed. In his magnum opus, De Revolutionibus, he placed the Sun in the middle of the cosmos. Copernicus nonetheless maintained perfect circular orbits, unaware of their mismatch with reality.
Half a century later, Johannes Kepler put matters right with his three laws of planetary motion—the first predictive equations in the history of science—one of which showed that the orbits are not circles but ovals of varying elongation. We have only just begun. Consider the Earth-Moon system. Meanwhile, not only do the Moon and Earth tug on each other, but all the other planets and their moons tug on them too.
Plus, each time the EarthMoon system takes a trip around the Sun, the orientation of the ellipse shifts slightly, not to mention that the Moon is spiraling away from Earth at a rate of one or two inches per year and that some orbits in the solar system are chaotic.
All told, this ballet of the solar system, choreographed by the forces of gravity, is a performance only a computer can know and love. If you find it, you move on to the next open question.
Nevertheless, one would be misguided to declare that Copernicus was wrong simply because his orbits were the wrong shape. His deeper concept—that planets orbit the Sun—is what mattered most. From then on, astrophysicists have continually refined the model by looking closer and closer. Copernicus may not have been in the right ballpark, but he was surely on the right side of town.
So, perhaps, the question still remains: When do you move closer and when do you take a step back? A block ahead of you is a silver-haired gentleman wearing a dark blue suit. If you stand 10 feet away, you might see men in tophats, women in long skirts and bustles, children, pets, shimmering water. Which way best captures how nature reveals itself to us? Both, really. Almost every time scientists look more closely at a phenomenon, or at some inhabitant of the cosmos, whether animal, vegetable, or star, they must assess whether the broad picture—the one you get when you step back a few feet—is more useful or less useful than the close-up.
The urge to pull back is strong, but so, too, is the urge to push ahead. For every hypothesis that gets confirmed by more detailed data, ten others will have to be modified or discarded altogether because they no longer fit the model.
And years or decades may pass before the half-dozen new insights based on those data are even formulated. Case in point: But before Galileo first looked up with a telescope in , nobody had any awareness or understanding of the surface, composition, or climate of any other place in the cosmos.
In Galileo noticed something odd about Saturn; because the resolution of his telescope was poor, however, the planet looked to him as if it had two companions, one to its left and one to its right. When sorted out and translated from the Latin, the anagram becomes: At one stage they looked like ears; at another stage they vanished completely. As Galileo had done half a century earlier, Huygens wrote down his groundbreaking but still preliminary finding in the form of an anagram.
Within three years, in his book Systema Saturnium, Huygens went public with his proposal. Twenty years later Giovanni Cassini, the director of the Paris Observatory, pointed out that there were two rings, separated by a gap that came to be known as the Cassini division. By the end of the twentieth century, observers had identified seven distinct rings, lettered A through G.
Not only that, the rings themselves turn out to be made up of thousands upon thousands of bands and ringlets. Pioneer 11 in , Voyager 1 in , and Voyager 2 in Those relatively close inspections all yielded evidence that the ring system is more complex and more puzzling than anyone had imagined. For one thing, the particles in some of the rings corral into narrow bands by the so-called shepherd moons: The gravitational forces of the shepherd moons tug the ring particles in different directions, sustaining numerous gaps among the rings.
Density waves, orbital resonances, and other quirks of gravitation in multiple-particle systems give rise to passing features within and among the rings.
The cosmo-chemistry of the environment suggests that Saturn might once have had several such moons. Saturn, by the way, is not the only planet with a ring system. Close-up views of Jupiter, Uranus, and Neptune— the rest of the big four gas giants in our solar system— show that each planet bears a ring system of its own.
As we will see in Section 2, many comets and some asteroids, for instance, resemble piles of rubble, and they swing near planets at their peril. I recently received some upsetting news about Saturn from a colleague who studies ring systems.
He noted with sadness that the orbits of their constituent particles are unstable, and so the particles will all be gone in an astrophysical blink of an eye: My favorite planet, shorn of what makes it my favorite planet! Turns out, fortunately, that the steady and essentially unending accretion of interplanetary and intermoon particles may replenish the rings. The ring system—like the skin on your face—may persist, even if its constituent particles do not.
What kind of news? Here and there in all those rings are features neither expected nor, at present, explainable: All these new data will keep Porco and her colleagues busy for years to come, perhaps wistfully recalling the clearer, simpler view from afar.
But suppose you have no technology. Suppose all you have in your backyard laboratory is a stick. What can you learn? With patience and careful measurement, you and your stick can glean an outrageous amount of information about our place in the cosmos.
The stick just has to be straight. Hammer the stick firmly into the ground where you have a clear view of the horizon. Your caveman laboratory is now ready. The shadow will start long, get shorter and shorter until the Sun reaches its highest point in the sky, and finally lengthen again until sunset. Collecting data for this experiment is about as exciting as watching the hour hand move on a clock.
But since you have no technology, not much else competes for your attention. Notice that when the shadow is shortest, half the day has passed. And on two days a year the shadow of the stick at sunrise points exactly opposite the shadow of the stick at sunset.
When that happens, the Sun rises due east, sets due west, and daylight lasts as long as night. On all other days of the year the Sun rises and sets elsewhere along the horizon. After they cross the east-west line again, the southward creeping eventually slows down, stops, and gives way to the northward creeping once again.
The entire cycle repeats annually. What else to call that day but the winter solstice? An expensive chronometer would help here, but one or more well-made hourglasses will also do just fine. Either timer will enable you to determine, with great accuracy, how long it takes for the Sun to revolve around Earth: Averaged over the entire year, that time interval equals 24 hours, exactly. Back to you and your stick. Establish a line of sight from its tip to a spot on the sky, and use your trusty timer to mark the moment a familiar star from a familiar constellation passes by.
Then, still using your timer, record how long it takes for the star to realign with the stick from one night to the next. That interval, the sidereal day, lasts 23 hours, 56 minutes, and 4 seconds. 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. Omitting intermediate steps, the Sun simply says: 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. The inside of a star is a hurly-burly of atoms, electrons and aether waves.
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. As we watch the scene we ask ourselves, can this be the stately drama of stellar evolution?
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.
Another planet, Jupiter, had moons all of its own, and Galileo discovered the four largest: 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 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: 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: 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: 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. Harriet, Jo-Ann, and Ralph each have one: 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. Earth-crossing killer asteroids, comets, and myriad planetary moons. 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. Once you have submitted your order you will receive confirmation and status update emails.
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