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Accepted, Eligibility for PayPal Credit is determined at checkout. TAU was also to be a platform for other astrophysics and astronomy projects, examin- ing the heliopause, the interstellar medium beyond it, and, if pos- sible, the planet Pluto. Using advanced optical communications to transmit its findings, the 1,2oo-kilogram probe would travel 1, AU in a fifty-year flight. Both Interstellar Precursor and TAU were designed around nuclear-electric propulsion systems, the nuclear version of a technology that would later be success- fully tested aboard the Deep Space 1 spacecraft.
Solar sails unfurled close to the Sun also remained an option. But it is one thing to design hypothetical missions, quite another to be given an exhortation from the top to make them happen. Taken off guard, many NASA scientists embraced Goldin's goal while acknowledging the immensity of the task. Later that year, Goldin made it clear that the stars might require entirely new thinking. All these breakthroughs could be employed in an interstellar probe he envisioned as a "Coke can-sized spacecraft" that essen- tially builds itself into a star probe using carbon, iron, and other materials on a nearby asteroid.
Such a spacecraft sounds like an ambitious dream, but it could be possible if we effectively utilize hybridized technologies. The team, wrote the Jet Propulsion Laboratory's Richard Mewaldt, had been charged with defining the first mission to explore the local interstellar medium, reaching a distance some AU from the Sun within fifteen years by using a solar sail for propulsion. The JPL probe, as outlined in a concept briefing Forward delivered to the IPSTDT at Beckman Institute Auditorium at the California Institute of Technology on February 16, , would be designed to explore the structure of the helios- phere and its interaction with the interstellar medium, while studying the astrophysical processes occurring in both, all of which would have implications for our understanding of the ori- gin and evolution of matter in the Galaxy.
Such a mission would be the first time scientists could measure the plasma, neutral atoms, magnetic fields, dust, energetic particles, cosmic rays, and infrared emissions flowing from our solar system into surrounding space. This would answer many questions about how the Sun interacts with the rest of the Galaxy as well as how matter is distrib- uted throughout the outer solar system. A physicist, aerospace engineer, inventor, and popular science fiction author, he had pioneered futuristic notions from antimat- ter to gravitational engineering, space tethers, and rocketless propulsion.
In he was asked by the House Committee on Science and Technology to come up with a national space pro- gram for interstellar exploration, the first time to my knowledge that such things as fusion rockets and laser-pushed lightsails have appeared in the Congressional Record. Audacity defined the man, as witness these remarks to the committee, which are worth quoting at some length: A national space program for interstellar exploration is pro- posed.
The program envisions the launch of automated interstellar probes to nearby stellar systems around the turn of the century, with manned exploration commencing 25 years later. The program starts with a year period of mis- sion definition studies, automated probe payload definition studies, and development efforts on critical technology areas. The funding required during this initial phase of the program would be a few million dollars a year. As the auto- mated probe design is finalized, work on the design and fea- sibility testing of ultra-high velocity propulsion systems would be initiated.
Five possibilities for interstellar propul- sion systems are discussed that are based on 1o- to 3o-year projections of present-day technology development pro- grams in controlled nuclear fusion, elementary particle physics, high-power lasers, and thermonuclear explosives. Annual funding for this phase of the program would climb into the multibillion-dollar level to peak around A. Development of man-rated propulsion systems would continue for 20 years while awaiting the return of the automated probe data. Assuming positive returns from the probes, a manned exploration starship would be launched in A.
All this at a time when the war in Vietnam had just ended and the United States was in full retreat from the Moon. If an idea had the stamp of future breakthrough on it, chances were Forward had already written a paper on it. Flamboyant, given to loud vests made for him by his wife, highly visible with his shock of white hair, Forward would become a fixture on the interstellar research scene, not to men- tion the numerous public meetings and science fiction conven- tions he attended.
A scientist to the core, he saw his writing as a separate and distinct occupation. Forward's presentation on the JPL interstellar probe to the team assembled at the California Institute of Technology that day in early was a stunner. Having outlined the mission's science objectives and constructed a hypothetical payload of instruments, he went on to provide a solar sail technology roadmap that began with a sail demonstration in an upcoming mission called Geostorm, which would use a sail to position a payload that would provide early warning of solar storms for military and civilian satel- lite users.
Forward envisioned later science missions within the solar system ranging from sampling a comet to a spacecraft designed to land on Jupiter's moon Europa. What he called "interstellar medium exploration" used a solar sail to power the JPL mission under discussion, but he saw future missions to the Oort Cloud using a lightsail pushed by a beam oflaser power. The culmination would be the first true interstellar probe, a beamed lightsail four kilometers in diameter that would make a flyby of the Alpha Centauri system in forty years.
Such interstellar sails might one day be expanded to a behemoth 1,ooo-kilometer sail that he believed could reach stars up to forty light years away. The optimistic dates in Forward's presentation have already slipped he had spoken of sail demonstrations by , with launch of the heliosphere explorer by 2oo8, a schedule now obvi- ously impossible. But the first solar sail experiments in flight are upon us, with the development of the Planetary Society's Cosmos 1 sail and another privately funded sail by a Texas group called Team Encounter.
NASA's own plans call for flight testing of solar sails perhaps beginning as early as 2oo8, and the European Space Agency is also investigating sail technologies. No firm date on the development of JPL's interstellar probe can be given, but it is clear that the first spacecraft to use interstellar propulsion tech- nologies will be propelled either by a sail or a form of nuclear electric engine.
The work within an American space agency shouldn't disguise the fact that interstellar research is a truly international phenom- enon. Maccone and Matloff had studied sail designs for missions out to the AU point, the zone where the Sun's gravity acts like a lens that can be used to magnify distant astronomical objects. Matloff published an analysis of design options for such a probe, using a 10,ooo square meter sail as his baseline, and calculated a flight time of sixty years to the gravity focus.
Italian physicist Giovanni Vulpetti would draw on Maccone and Matloff's mission concepts to cre- ate a more conservative solar sail mission to the heliopause called Project Aurora. A sequence of future events began to take shape for interstellar theorists, although its dates could only be guesswork. A mission to penetrate the heliopause would go first, followed by a probe designed to study the Kuiper Belt. The Oort Cloud was a goal for a later probe, one that would probably not fly until mid-century.
The ultimate goal, Alpha Centauri, hovered like a beacon beyond the Oort Cloud mission. But that foundation has been under construction for a long time, and no one has worked at it with more eloquence or insight than Gregory Matloff. He brings not simply enthusiasm but genuine commitment to the notion that humanity's future is in the stars. And over the past three decades, he has emerged as a key figure in interstellar studies. Matloff found his subject when, as a graduate student at New York University, he read James Strong's book on interstellar probes, Flight to the Stars.
Having found an error in Strong's discussion of fusion, he wrote a paper comparing dif- ferent methods of using excess fusion energy. Finishing a PhD on planetary atmospheres at NYU, Matloff was soon presenting papers on concepts that were unashamedly futuristic. This was the s, a time when the line between science and science fic- tion seemed to be defined by Gerard O'Neill, who envisioned enormous colonies at the gravitationally stable Lagrangian points in nearby planetary space.
Matloff would imagine O'Neill's colony designs wedded to propulsion systems of the sort envi- sioned by Project Orion and a later design called Daedalus. The result was a "worldship," an interstellar ark that would carry colonists on a thousand-year journey to another star, using a form of electromagnetic braking of the sort later refined by Robert Zubrin and Dana Andrews to decelerate upon arrival.
The idea was straight out of Robert Heinlein, although the world- ship Heinlein envisaged in his story "Universe" later reshaped as the novel Orphans of the Sky was nothing like an O'Neill colony, with its vast farmlands, rivers, and almost pastoral ecology. Brian Aldiss would work this theme in far different ways in his novel Non-Stop published in the United States as Starship , but both stories played off the idea of a multi-genera- tional voyage whose crews have gradually lost the memory of their mission. Matloff's daring was to find plausible scientific ways of getting a worldship to its destination, demonstrating that in terms of design, a starship could be extrapolated from today's physics.
Concepts mutate and re-emerge, old notions take on vibrant new forms. And while fusion seemed to be stuck in the endless attempt to reach the breakeven point, beyond which more energy comes out than goes into making the reaction, the hot technology of the late o's was the solar sail. Proposed by a team at the Jet Propulsion Laboratory for NASA's never-flown Halley's Comet mission, sail technologies were a more ingenious and considerably more plau- sible way to accelerate Matloff's worldship. The physicist now took upon himself the challenge of designing a thousand-year journey that would reach Alpha Centauri pushed by nothing more than sunlight.
To gain the needed speed, Matloff's starship would perform what science fiction writer and fellow physicist Gregory Benford came to call a "sun-diver" maneuver, unfurling its sail as the vessel all but skimmed the Sun's corona before heading out of the solar system. Matloff's analysis of such missions made his participation in any interstellar spaceship design a priority. Active as ever, he now looks back on that effort with a certain wistfulness. We really believed we could skip a lot of that.
Which of course was naive. We came to realize that we have to test out the concept much closer to home. Goldin had recently resigned from his post at NASA, and while the agency's theorists appreciated his enthusiasm for the task, a quick push for Alpha Centauri was clearly not in the cards.
I wanted to learn what had happened to the interstellar idea. Had it simply been abandoned, or modified so extremely as to be unrecognizable? Was an interstellar probe even possible? This book is the result of my attempts to find answers. I had been a reader of science fiction since boyhood, attracted by magazines like Astounding Stories later Analog Science Fic- tion and Fact , edited by the canny John Campbell.
I had read H. Gold's Galaxy with pleasure as it pushed past overt science into the mechanics of future societies, probing their assumptions, looking at what strange outcomes do to human relationships. In these and other magazines, many of whose space-themed covers took my breath away, starflight was more or less a given. It had been so since , when Edward E. Smith, a Wisconsin-born chemist who specialized in doughnut mixes, took rockets out of interplanetary orbits and opened up the universe in his Skylark of Space.
And in the way of science fiction readers, I had developed a healthy dualism. There was the real world, and there was the future- or sometimes parallel-world of science fiction. As I grew older, I never lost either my fascination with starships, or my conviction that while we would one day have them, their tech- nology was so far beyond our own as to be, in Arthur Clarke's fine phrase, "indistinguishable from magic.
Its physicists, astronomers, and engineers worked in the pages not of science fiction magazines but learned journals with titles like Acta Astronautica, The Journal of Spacecraft and Rockets, Icarus, and even the prestigious Physical Review. They seemed to share an assumption with Robert Forward, who wrote in that" Just as science fiction had its classics of starflight, like Paul Anderson's dazzling tour of the universe in his novel Tau Zero, so this other culture, poised between science fiction and physics, had developed its own literature studded with keepers.
Many of these appeared in the Journal ofthe British Interplanetary Society, the publication of an influential group of space enthusiasts whose work before and after World War II brought public attention and professional respect to space travel. Arthur C. Clarke was a member, and it was to the British Inter- planetary Society that he would first present many of his ideas. JBIS has become the key interstellar periodical; the titles of its arti- cles out-do anything John Campbell ever published in Astound- ing, and it was the BIS that produced the first full-length study of a robotic interstellar probe, the fusion-driven Project Daedalus.
Who could fail to be struck by titles like A. Stimets and E. The literature seemed inexhaustible. Robert Forward and astronautical engineer Eugene Mallove, who published sev- eral bibliographies of interstellar studies in JBIS, were eventually overwhelmed by the page count and forced to abandon the effort-their bibliography included fully 2, items in sev- enty subject categories.
Each paper led to others: I found studies in profusion on propulsion, communication systems, interstellar navigation, shields to protect against collisions with interstellar dust-all these explored every facet of building and flying a probe to nearby stars. What was afoot was foundation building. When we do one day go interstellar, we will draw from these papers the basic principles that will guide the mission.
I also discovered there was a parallel story, one that starts not with extrapolation and theory but current technology. We have been building space probes for a long time, long enough to know what sort of planning and experiment must go into every design. An Alpha Centauri probe, whether it flies in fifty years or a hun- dred, will grow organically out of concepts that are being tested in laboratories and in some cases flown on missions today.
Deep Space 1 also carried an optical navigation system that gave promise of autonomous oper- ations, allowing a distant probe to compute and correct its own course rather than waiting on signals that might take days, or much longer, to reach the vehicle from Earth. Add a raft of other tests, including status monitoring systems for on-board condition reports, concentrated solar arrays that cost less but generate power more efficiently than conventional systems, and "agent" software that is designed to allow a spacecraft to operate without human intervention, and you have a design for the future.
When it was retired from its extended mission in late , Deep Space 1 had returned images of Comet Borrelly that were among the best ever seen of a comet, and had successfully completed technology tests of hitherto unproven flight systems. Managed by the Jet Propulsion Laboratory, Deep Space 1 was the first of NASA's so-called New Millennium missions, a pro- gram designed to test and validate new technologies so they could be used in future missions without risk.
And risk is a big word inside NASA. No one wants to sign off on a mission that fails; managers are rewarded for success, not for risk-taking. The result is that the agency has often been criticized for using com- ponents with a long history, and putting more emphasis on sys- tem redundancy than innovation. Some of the technologies the Jet Propulsion Labora- tory managed on Deep Space 1 may lead to key components for interstellar probes. You would think that if there were a place where science met sci- ence fiction, it would be at the Jet Propulsion Laboratory, where so much of NASA's work on robotic space exploration proceeds.
We protect those things that are closest to us, and it may be that working on, say, a Mars rover makes it more likely that you will be less willing to have your work taken lightly, as mere fodder for science fiction buffs. In any case, wild speculation has little place in the realm of Voyager, Galileo, and Cassini, whose mis- sions proceed with precision measurement, quantified data, and an uncanny touch for squeezing information out of distant signals.
He is an earnest, friendly man whose passion for ideas drives his rapid-fire speech. Microwave physicist James Benford, discussing methods of solar sail deployment in space, told me that he favors spinning the sail to ensure an even distribution of its material. And it becomes clear that when discussing issues involving NASA in deep space, Hoppy Price is a man to be reckoned with.
Deep space exploration in the next forty years will almost cer- tainly involve both solar sails and nuclear electric engines, even as more exotic possibilities are tested in the laboratories. Price's time is spent looking at upcoming missions that might use sail technology, missions like Geostorm, designed to provide early warning of solar flares by using a solar sail to approach to no more than a fifth of the distance that the Earth is from the sun, using photon pressure to balance the sun's gravity.
Or the Solar Polar Imager, a sail mission that approaches the sun from a spiraling, equatorial orbit that is then altered to push the spacecraft into a circular polar orbit perpendicular to the ecliptic. No currently available ion drive or chemical rocket could achieve that kind of orbit because of the large change in velocity required. Acknowledging the need for a space-based infrastructure to support a Centauri mission, he thinks the time frame of the mission is an equal challenge.
Because we're also working on the beginnings of a program to build very long lifetime electronics, systems that can operate for up to two hundred years. If you let yourself take two, even three hundred years to get there, the problem of propulsion becomes a bit easier. We as a culture may have to start thinking in terms like that. The average worker on a medieval cathedral didn't live to see it com- pleted. My view is that the first time we send something to Alpha Centauri, it will probably take hundreds of years to get there.
A robotic interstellar probe challenges our commitment to the future. At Johns Hopkins, physicist Ralph McNutt has analyzed strategies for an interstellar precur- sor mission that would both explore the near interstellar medium and set the stage for future interstellar operations. McNutt's work, prepared for NASA's Institute for Advanced Concepts, envisions a heavily shielded spacecraft using a gravity assist from the Sun after first being assisted by an initial flyby of Jupiter to facilitate the near-Sun approach , closing to within three solar radii.
At this point, the probe is given an additional kick by the burn of a solar-thermal rocket using the sun's heat to energize a gas propellant, or conceivably using a scaled-down "Orion" approach with nuclear explosions behind the craft to push it , then separating from the propulsion system to begin its flight toward the interstellar medium. McNutt's probe would pioneer the technologies required for long-term autonomous spaceflight, paving the way for a mission to Epsilon Eridani late in the twenty-first century.
The monuments of antiquity- the Great Pyramid of Cheops, the cathedral of Chartres, or the Shinto temple complex in Japan known as the Ise Shrine-consumed the work of generations. Indeed, the Ise Shrine still does, its all-wood structure being care- fully rebuilt every twenty years for the last thousand. One way to view an interstellar robotic probe is as a cross between a scientific mission and a gift to the human future.
Thus McNutt writes about a second generation interstellar probe traveling at ten times the speed of the precursor. At AU per year, the first crossing to another star could be made in approximately 3. Though far from ideal, the stars would be within our reach. For one thing, it is a star of high biolog- ical interest, surveyed by Frank Drake in his Project Ozma search for extraterrestrial radio signals and studied repeatedly as a possi- ble site for an Earth-like planet.
But just as significantly, it lines up well with the plane of the ecliptic. The Earth orbits at thirty kilometers per second, and a spacecraft would have that initial velocity as it begins its journey toward the Sun in the plane of the ecliptic to get a gravity boost to an even higher velocity. Although Epsilon Eridani is considerably further away than Alpha Cen- tauri That makes Epsilon Eridani stand out in comparison to other possible candidates, especially the obvious one. I've got to make a big bend to turn in its direction, so I lose all the angular momentum I gain by choosing a target that's close to the plane of the ecliptic.
It was amazing to me when I studied it that it made as much difference as it did. Do we have the sense of purpose as a species to plan and execute missions that would benefit descendants we will never know?
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The question would haunt my work on inter- stellar probes, coming up again and again in conversations with researchers. Some argue that a slow probe would inevitably be passed by the faster probes oflater generations, but progress is not always linear. Using the same logic, we who have already been to the Moon should have been on Mars by now.
There will come a time when we launch something in the teeth of possible futures; we'll also design it to do plenty of good science along the way. And while the emphasis in modern culture is surely on beat- ing the clock, projects do remain that are multi-generational by design. In Pune, India, scholars composing an authoritative dic- tionary of Sanskrit have labored for three generations-and six volumes-thus far and have succeeded in finishing only the first letter of the Sanskrit alphabet. Given that the long-dead lan- guage, the ancient literary language of Hindus, is laced with puns and infolded meanings that defy even the attempts of scholars to untangle, the completion of this project is surely decades-and probably centuries- off.
Yet the work of the Deccan College dic- tionary project is crucial for understanding aspects oflndian cul- ture, since Sanskrit remained in wide use until A. There is something deeply preservative, and deeply human, that guides such projects. In a similar way near China's Yunju monastery, Buddhist monks began preserving their scriptures in stone in an era when what is now Beijing province was the scene of widespread book burnings. Over 14, stone tablets are the result, an effort beginning in the early seventh century A.
Stewart Brand writes that the idea of a canon, a selection of the best that is known and thought, a selection that is meant to be passed from generation to generation, is one of the great instru- ments of civilization. But hopes for a faster mission have hardly been abandoned. Ralph McNutt's precursor probe is designed as a testbed for inter- stellar technologies as well as a science mission that can answer fundamental questions about the nature of the interstellar medium. Along the way, such a probe could examine the disposi- tion of interstellar hydrogen as a way of evaluating the possibili- ties of a Bussard-style ramjet, the kind of vehicle that could reduce flight times to nearby stars to decades instead of millen- nia.
The goal of making an Alpha Centauri crossing within the lifetime of a researcher remains alive not only in offices search- ing for major innovations-NASA's Breakthrough Propulsion Physics project recently terminated but hopeful of future fund- ing and its Institute for Advanced Concepts are just two of these- but in the scientific literature, where fast-mission con- cepts abound. Of all of these, none is more famous than Britain's Project Daedalus, the most comprehensive starship design study ever attempted, and still the most entertaining in its origins.
The work of the British Interplanetary Society, Project Daedalus was designed around a fusion drive that uses tiny pel- lets of fusion fuel instead of nuclear bombs. And unlike the labo- ratory environment that had spawned so much earlier work on propulsion systems, Daedalus was developed in informal meet- ings and conversations in English pubs. Counting Wernher von Braun among its members, the VfR had a similarly gutsy notion that passion and hard work could lead eventually to manned spaceflight. His job description covers everything from NASA's wildly successful Mars rovers to photovoltaic systems for generating power in space, and advanced concepts that range from laser- driven solar sails to cosmic strings and wormholes.
One suspects a few starship designs may have been jotted down by his prolific pen in pub-like venues at science fiction conventions, as well as the far more academic gatherings like the Space Technology and Appli- cations International Forum held annually in New Mexico, where deep space propulsion ideas flow like wine. So respected is Landis among those who dream of the stars that Robert Forward, upon turning his attention to space tethers at age seventy, specifi- cally tagged him as his successor in the field of interstellar studies.
In an earlier time, a man like this would likely have been one of the British Interplanetary Society's charter members. Like Landis, the BIS has a history of probing the unthinkable, whether in pubs or elsewhere. Founded in by P. Cleator, the Soci- ety was first headquartered in Liverpool before moving to Lon- don in It was an early advocate of manned travel to the moon and planets whose members included, in addition to Arthur C.
Clarke, such visionaries as fellow science fiction writer John Wyndham and Val Cleaver, an engineer who in the s played a role in a British intermediate-range missile program called Blue Streak. These stories capture the atmosphere of the early BIS gatherings as the polymath Harry Purvis spins yarns about improbable scientific advances to a bemused clientele. But there was more happening at the Mason's Arms than ale drinking and leg pulling.
The group was intent on working out the practical problems of space flight in an era when the piston- driven airplane still dominated the sky. That work was temporar- ily interrupted by World War II, but the BIS remained together in the postwar years to make the case for space exploration, playing a role in keeping German rocket scientists who had been recruited by Britain and America connected as their lines of research began to diverge.
While papers were proliferating on specialized interstellar topics, no integrated study of a mission had ever been undertaken. Bond's argument was straightforward: Technology had advanced to the point where a realistic interstellar design could be com- pleted without assuming anything more than we already knew about physics. The target would be Barnard's Star, at 5.
The flight time was fifty years, the maximum mission length Bond deemed acceptable because it allowed the mission to be flown within the average lifetime of a researcher working on the project. Daedalus would accelerate to 12 percent of the speed of light roughly 36,ooo kilometers per second and perform a flyby of Barnard's Star, making the encounter time within the sys- tem a matter of days, although the study included autonomous probes that would be deployed to nearby planets as Daedalus approached the target.
As opposed to the pulsed fusion engines of the main craft, the probes would use nuclear-powered ion propulsion systems. The Daedalus starship's thrust period was envisioned as four years, during which pellets of deuterium and helium-3 would be detonated every second in the combustion chamber. The two- stage craft, both stages using the same fusion-pulse design, was to be constructed in orbit around Jupiter. It would weigh 54, tons, of which fully 5o,ooo were fuel, with a scientific payload of tons. Described in a supplement to JBIS that remains one of the landmarks of interstellar research, the Project Daedalus study was nowhere more breathtaking than in how it envisioned producing its fuel.
Thus the key ingredient-3o,ooo tons of helium would be mined from the atmosphere of Jupiter. Today there are other fusion concepts, some of them includ- ing the use of antimatter as a catalyst, and a host of propulsion ideas using completely different technologies. The candidate sys- tems-solar sails, beamed lightsails, fusion, antimatter, and inter- stellar ramjets in myriads of variations-are examined in the chapters that follow, along with thoughts about their current development from the scientists who study them.
Wildcard con- cepts of exceeding interest also make an appearance, including attempts to manipulate inertia and pull energy out of raw vac- uum. Propulsion may be nine-tenths of the battle, but we will also consider how to make probes that repair themselves, and the intricacies of navigating between the stars. Science fiction has created many an image of such ships. Today's research some- times evokes those images, and just as often creates an even bolder imagery of its own.
Any one of the advanced ideas being bandied about in labora- tories and research centers could produce a discovery that changes everything, so it is unwise to become too attached to a sin- gle means of thrust. I had expected this, and knew that today's sci- entists would have weighed a probe like Daedalus and found countless ways to improve it.
What I hadn't expected was the true wildcard in interstellar study: nanotechnology. For if the biggest issue with sending a probe to another star is the vast expense of pushing payload, then finding a way to shrink the payload down to almost nothing may be a prerequisite. The final chapter of this book will examine interstellar probes the size of sewing needles, sent in their billions on a mission of supreme redundancy, probes that can spawn other probes and build their own communications devices.
If this is a bizarre future, it is no more strange than Project Daedalus would have looked to the designers of the DC Even as a starship embodies our dreams, it also casts light on our history. Lord Collingwood was Nelson's second in command at the battle of Trafalgar, taking command of the fleet when Nelson was mortally wounded. He would go on to encourage plantings of oaks that would be ready for the Navy a hundred and fifty years after his death. In an era of quickly fabricated materials, we forget our once deep reliance on the slow processes of nature, and the need to adapt to their rhythms.
Interstellar flight demands perspectives as profoundly attuned to its goals as those of Collingwood's foresters, and a commitment to what Tennyson once called "the long result of time. Mader's huge spaceship was a sphere feet in diameter that used obscure antigravity techniques to travel to Alpha Centauri at several times the speed of light. Other writ- ers had attempted interstellar journeys, in particular the French authors C.
Defontenay in Star ou Psi de Cassiopee: Histoire Merveilleuse de l'un des Mondes de l'Espace , which also used antigravity in its explorations of the planetary system Psi Cassiopeia, and Camille Flammarion in Lumen , a novel featuring a journey to Capella. But Mader's starship Sannah was the forerunner of all of today's science fictional journeys to the nearest stellar system. Alpha Centauri is an obvious target. At light years, it is the closest stellar system known.
Of the two larger stars in the system, Alpha Centauri A, the brightest, closely resembles our Sun in size, absolute magnitude, and spectral type which reflects the star's color and hence temperature. Recent research has raised doubt about whether Proxima is actually part of the Alpha Centauri system or simply a passing star that is not gravitationally bound to the other two. Located in the southern constellation Centaurus, Alpha Cen- tauri is also known as Rigil Ken taurus, meaning "foot of the cen- taur" drawn from the Arabic Al Rijl al Kentaurus.
The system may have been an object of worship to ancient Egyptian civiliza- tions along the Nile. In fact, its first emergence in the morning sky at the autumn equinox has been considered a marker for the orientation of several fourth millennium B. Alpha Centauri is of more recent historical interest because of how its distance was first measured.
It was in that Thomas Henderson, a Scottish lawyer who became director of the Royal Observatory at the Cape of Good Hope in South Mrica, sub- jected the system to distance measurements. Centauri was an obvious choice, since south of 40 degrees north latitude, with its two largest stars appearing as a single star to the unaided eye, it is the third brightest star in the sky after Sirius and Canopus. At nth magnitude, Proxima Centauri cannot be seen without a tele- scope.
Henderson was unaware of the efforts of two other astronomers- Friedrich Georg Wilhelm von Struve and Friedrich Wilhelm Bessel-to make the first measurement of the distance to a star, and while he completed his observations first, Henderson's accomplishment was upstaged by Bessel's announcement of the distance of the star 61 Cygni, some The work of all three men made use of a method known as stellar parallax. Henderson observed the position of Alpha Cen- tauri, waited six months so that the Earth would be on the oppo- site side of the Sun in its orbit, and then made the measurement again.
The star had appeared to move by three-quarters of a sec- ond of arc against the background stars, indicating that it was much closer than they were. Using basic principles of trigonome- try and the fact that the Earth's orbit is million kilometers million miles in diameter, Henderson could calculate its distance: 41 trillion kilometers 25 trillion, million miles. The method could be improved if we had a longer baseline, which is one great value of an interstellar probe-its distance from the Sun would allow much more accurate calculations for stars far- ther away.
If stars are measured according to their absolute magnitude actual brightness, as opposed to "apparent" magnitude, which is brightness as seen from Earth and spectral type, a plot emerges called the Hertzsprung-Russell diagram. Named after the astronomers Ejnar Hertzsprung and Henry Norris Russell, whose independent work led to its discovery, the diagram shows that most stars on such a plot fall into a more or less diagonal line slop- ing downward called the "main sequence,'' showing that lumi- nosities drop off as surface temperature decreases.
Above the main sequence are large, cool stars, and below are the dim, small white dwarf stars. Where a star is plotted on the Hertzsprung-Rus- sell diagram tells us much about the star's stability. Once the Sun, for example, leaves the main sequence in roughly five bil- lion years, it will enter a red giant phase and, having burned the bulk of its fuel, will end its life as a white dwarf.
When choosing a mission destination, we clearly want to focus on main sequence stars similar to the Sun whose stability suggests that any planets around them might harbor life. Ranging from hottest to coolest, the main sequence spectral types are designated by the letters 0, B, A, F, G, K, and M. Albedo is commonly used in astronomy to describe the fraction of sunlight reflected by planets, satellites and asteroids: rocky bodies have low values whereas those covered with clouds or comprising a high percentage of water-ice have high values. The average albedo of the MOON, for example, is just 0.
Albert was an anomaly for many decades in that it was numbered and named after its discovery in but subsequently lost. Despite many attempts to recover it, Albert escaped repeated detection until the year His principal work was the New General Catalogue of Double Stars , based largely on data he gathered at Lick beginning in It contains magnitudes and separations for more than 17, double stars, including many true binary systems. Aitken discovered more than doubles, and computed orbits for hundreds of binaries. AI Velorum stars belong to the disk population and are not found in star clusters.
They are sometimes known as dwarf Cepheids. It is only 3 km 1. Albategnius is an ancient impact site, and its eroded rims display landslips and valleys.
A massive pyramid-shaped mountain and many bowl craters mark the central floor. Albireo is a beautiful double star of contrasting colours. It comprises an orange giant the brighter component, spectral type K3 II twinned with a companion of mag. The name Albireo is a medieval corruption, and is meaningless. Alcor The star 80 Ursae Majoris, visual mag. Alcor is a spectroscopic binary, though no accurate data are known.
At visual mag. In Greek mythology, Alcyone was one of the seven daughters of Atlas and Pleione. It is an orangecoloured giant of spectral type K5 III. It marks the eye of Taurus, the bull. Its true luminosity is about times that of the Sun. Although Aldebaran appears to be a member of the V-shaped Hyades cluster, it is a foreground object at about half the distance, superimposed by chance.
The name comes from the. Red areas are bright and show where there is dust while blue areas show where the underlying, darker rocks have been exposed.
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He made the first truly accurate calculations of the solar tropical year Defined as the ratio of the. Its name comes from an Arabic expression referring to a forearm. The electrically conducting plasma is linked to and moves with the magnetic field. The plasma follows the oscillations of the magnetic field and modifies those oscillations. Here, he is seen with the Solar Wind Composition experiment.
Small telescopes show it to be a beautiful double star with golden-yellow components of mags. The pair form a genuine binary with an orbital period of nearly It is now known, however, that Algol is somewhat atypical of its eponymous subtype. Gradually, the concept of an eclipsing companion became accepted and was finally confirmed when, in , Hermann VOGEL showed that the radial velocity of Algol varied with the same period as that of the eclipses.
By this time, Algol was known to be a triple system. In F. Fourteen years later he noted that the period between the times of minima varied in a regular fashion with a period of about days. This was attributed to the variation in the distance that the light from the system had to travel because of orbital motion around the common centre of gravity with a third star Algol C.
In the Russian astronomer Aristarkh Belopolski — confirmed the existence of Algol C by showing that radial-velocity variations in the spectral lines of Algol also had a period of 1. Several years later, Joel STEBBINS, a pioneer in stellar photometry, found that there was a secondary minimum of much smaller amplitude occurring exactly halfway between the primary eclipses. This showed for the first time that the companion was not dark at all, but merely much fainter than A. Photoelectric observations showed the depth of the secondary minimum to be 0.
This was interpreted as a reflection of light from the body of star B. There are two stars, of spectral types B8 and G, rotating about each other. The B8 star is a dwarf and is the visible component.
The fainter star whose spectrum was only observed directly for the first time in is a subgiant. Hipparcos data give a distance to Algol of 93 l. This corresponds to luminosities of and 3 for A and B respectively. From the length and depth of the eclipses, sizes of 2. The corresponding masses are 3. Thus, if two stars form together from interstellar material, the more massive of the two should evolve more quickly.
Optical spectra have shown very faint lines, which are thought to be emitted by a faint ring of material surrounding star A. Algol C was first resolved by speckle interferometry in and on several occasions since. The real nature of the Algol system is still far from clear. Even after years of continuous observation it still evokes considerable interest from astronomers. The light-curves of Algol stars. Almagest exhibit distinct, well-separated primary minima. Secondary minima may be detectable, depending on the characteristics of the system.
Outside eclipses, the lightcurve is essentially flat, although it may exhibit a small, gradual increase and decrease around secondary minimum, which is caused by the reflection effect, where light from the bright MAIN SEQUENCE primary irradiates the surface of the cooler secondary, thus raising its temperature and luminosity.
When the mass-transfer rate drops, the accretion disks disappear to reveal the unevolved stars, and the systems display all the characteristics of an Algol-like binary. If the main-sequence star in an Algol system is comparatively massive, it will evolve rapidly and expand to fill its Roche lobe while the companion star is still filling its own Roche lobe.
When the primary finally does expand to become a RED GIANT, gas flows across the inner Lagrangian point and goes into orbit about the white dwarf, forming an accretion disk.
However, most of these systems are not eclipsing pairs. It is important to note that eclipsing variables only appear to fluctuate in light because of the angle from which they are observed. Instruments include a element ARRAY of 3-m ft dishes for solar observations and a m ft fully steerable radio dish for studies of stars and galaxies. The ARO began work in , and the m dish was built in The name comes from an Arabic term that is thought to refer to the neck of a camel, from a former constellation in this area. It is one of the so-called peculiar A stars, of spectral type A0p with prominent lines of chromium.
Its alternative name, Benetnasch, is derived from an. Arabic phrase referring to a group of mourners accompanying a coffin formed by the quadrilateral of stars which is now known as the bowl of the PLOUGH commonly referred to in the US as the Big Dipper. It has a mass of c. A complex igneous rock, it has suffered both thermal and shock processes.
In composition, it is an orthopyroxenite rich in carbonates, which form patches up to c. Few hydrated minerals have been identified amongst the alteration products in ALH , so it has been proposed that the carbonates were produced at the surface of Mars in a region of restricted water flow, such as an evaporating pool of brine. Tiny structures c. Allegheny Observatory Observatory of the University of Pittsburgh, located 6 km 4 mi north of Pittsburgh. The observatory, which dates from , became part of the university in During the s its director was James E.
Later, Allegheny was equipped with the inch cm Thaw telescope the third-largest refractor in the USA and the inch 0. More than 2 tonnes of material is believed to have fallen. ALMA Abbreviation of. It is a multiple star, the two brightest components of which, mags. The fainter star has a close 6th-magnitude blue companion that orbits it every 61 years. Its name comes from the Arabic referring to a caracal, a wild desert cat, and is also spelled Almach and Alamak. Almagest Astronomical treatise composed in c. In its various forms the Almagest was a standard astronomical textbook from late antiquity until the Renaissance.
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It was subsequently lost to the West but was treasured in the Islamic world; it was reintroduced to European scholars via Moorish Spain in the form of a translation of the Arabic version into Latin completed in by Gerard of Cremona c. A blue-white supergiant, spectral type B0 Ia, it is the central star of the three that make up the belt of Orion and is marginally the brightest of them. It is a binary, with individual components of mags. A telescope of mm 3-in. The majority of the bright peaks have altitudes between and m — ft , but some are significantly higher: Mount. Varying in width from 7 to 18 km 4—11 mi , it irregularly tapers away from Mare Imbrium.
Alpha Unofficial name for the. Periods range from 0. The subtype ACV0 exhibits additional lowamplitude c. The meteor stream may be associated with the short-period 5. Small telescopes reveal that it is a triple system. The two brightest components are of solar type, mags. The shower produced outbursts of more substantial activity in , , and , suggesting a ten-year periodicity with several stronger displays having been missed.
In rates of one or two meteors per minute were sustained for only a short interval. Helium is the second-most abundant element after Hydrogen , so alpha particles are found in most regions of PLASMA, such as inside stars, in diffuse gas around hot stars and in cosmic rays.
Alpha particles are also produced by the radioactive decay of some elements. In the. The circular central area has a mean elevation of 0. More recently, the star has also become known as Gemma, since it shines like a jewel in the northern crown. The new Alphonsine Tables, incorporating ten years of revised observations and completed in , were not superseded for almost years.
Its fault-dissected walls rise to over m 10, ft above the floor. Running nearly north—south across the floor is a ridge system, which is 15 km 9 mi wide and, at the point where it forms a prominent central peak, about m ft high. Within Alphonsus are a series of kilometre-sized elliptical features with haloes of dark material; they are oriented roughly parallel to the central ridge system and are considered by many planetary geologists to be of volcanic origin.
ALPO Abbreviation of. It is a close binary with a calculated orbital period of around years. The brighter component, of mag. In this work he identified the stars of each constellation by their Arab names, providing a table of revised magnitudes and positions as well as drawings of each constellation.
It is a white main-sequence star of spectral type A7 V, with a luminosity 10 times that of the Sun. They rise very steeply from the east to an average altitude of m ft , with highest peaks at — m 11,—13, ft. Many amateur instruments with altazimuth mountings can therefore be used for general viewing, but are not suitable for longexposure photography.
Historically, large professional telescopes were invariably built with massive equatorial mountings, which often dwarfed the instrument they held. The lightweight and simple nature of altazimuth mountings, combined with high-speed computers, has led to almost all modern instruments being built with altazimuth mountings.
On these telescopes, computers are used to control the complex three-axis motions needed for an altazimuth mount to track the stars. Both the altitude and azimuth axes are driven at continuously varying rates but, in addition, the field of view will rotate during a long photographic exposure, requiring an additional drive on the optical axis to. The altitude of a particular object depends both on the location of the observer and the time the observation is made. The observatory used several quadrants for measuring planet and star positions, the largest of which was 3.
The optical component to be aluminized is first thoroughly cleaned and placed in a vacuum chamber, together with pure aluminium wire, which is attached to tungsten heating elements. After removing the air from the chamber, the heating elements are switched on, vaporizing the aluminium, which then condenses on to the clean surface of the optical component. This forms an evenly distributed coating, usually just a few micrometres thick.
After a career as a portrait painter and engraver, Alvan Clark —87 started an optical workshop in under the family name with his sons, George Bassett Clark —91 and Alvan Graham Clark —97 , the latter joining the firm in the s. Alvan Graham Clark discovered over a dozen new double stars, including, in , the 8th-magnitude Sirius B. Amalthea was the fifth Jovian moon to be found, in by E. The discovery was made visually, the last such discovery for a planetary satellite. Amalthea has considerable surface relief, with two large craters, called Pan and Gaea, and two mountains, named Mons Ida and Mons Lyctos.
Some sloping regions appear very bright and green, the cause of this phenomenon being unknown. The reasons were political and economic, as successive governments operated low-taxation, low-state-spending policies that encouraged private rather than public initiatives. Amateur astronomy, while it existed on Continental Europe, was less innovative, largely because the governments of France, Germany and Russia taxed more heavily and invested in professional science as an expression of state power.
The United States had a mixed astronomical research tradition, with outstanding amateurs, such as the spectroscopist Henry DRAPER, engaged in front-rank research, and major professional observatories financed by millionaire benefactors. In the Victorian age, wealthy gentleman scientists were willing to spend huge sums of money to pursue new lines of research and commission ground-breaking technologies, such as big reflecting telescopes. The quality of Grand Amateur research enjoyed peer recognition from European and American.
This was, indeed, professional-quality research paid for by private individuals. The results of their researches transformed our understanding of the Universe. Yet Victorian Britain also saw a fascination with astronomy spreading to the less well-off middle and even working classes. School teachers, modest lawyers, clergymen and even artisans took up astronomy; the selfeducated telescope-maker John Jones worked for a few shillings per week as a labourer on Bangor docks, Wales.
People with modest and often home-made instruments especially after the silvered glass mirror replaced speculum in the s did not expect, like the Grand Amateurs, to change the course of astronomy, but enjoyed practical observation as a serious and instructive hobby. The big-city astronomical societies of Leeds , , Liverpool , Cardiff , Belfast c. Unlike the Royal Astronomical Society, they all admitted women as members.
These societies, which dominated amateur astronomy well into the 20th century, remained predominantly middle-class, and it was not until the major social and economic changes in Britain following that the demographic base of British amateur astronomical societies began to widen significantly.
The BAA established a system whereby amateurs would send their observations to a central clearing house where they would be synthesized by an expert and the collective results published. Amateur astronomy changed dramatically after World War II, and much of the emphasis moved across the Atlantic.
Ingalls — Now that inexpensive war-surplus optical equipment was widely available, it was no longer essential for an amateur astronomer to build a telescope from the ground up as a rite of passage. By the mids, a wide variety of commercial instruments had entered the marketplace;. The numbers of amateur observers grew rapidly, particularly in the United States. A watershed for professional—amateur collaboration came in with the establishment of the Moonwatch programme, in anticipation of satellite launches for the International Geophysical Year — The appearance of affordable charge-coupled devices CCDs in the final decade of the 20th century had an even greater impact on amateurs than had the warsurplus items of two generations before.
They allowed amateurs to become competitive with ground-based professionals in the quality of data obtained in such areas as astrometry, photometry and the imaging of Solar System objects. New organizations with new ideas sprang up. It encourages joint amateur—professional authorship of technical papers. Similar, though focused on campaigns to study cataclysmic variable stars, is the Center for Backyard Astrophysics.
One of the latest groups to form is The Amateur Sky Survey, a bold venture to develop the hardware and software needed to patrol automatically the sky in search of objects that change in brightness or move. As the present era of mammoth all-sky surveys from Earth and space culminates, the need for follow-up observations — particularly continuous monitoring of selected objects — will grow dramatically.
In a traditional sense, because of their numbers and worldwide distribution, sophisticated amateurs are ideally suited for such tasks, not as minions but as true partners with professionals. The challenge facing the entire astronomical community today is to educate both camps about rewarding possibilities through mutual cooperation. Ambartsumian, Viktor Amazaspovich —96 Armenian astronomer who became an expert on stellar evolution and founded Byurakan Astrophysical Observatory.
His development of the theory of radiative. Shown here is a radar image of the impact site. It is not clear whether this feature called Ida is the crest of a ridge or material ejected from the crater to its right. He greatly advanced the understanding of the dynamically unstable stellar associations and extended principles of stellar evolution to the galaxies, where he found much evidence of violent processes in active galactic nuclei.
It has primary and secondary minima, the latter sometimes disappearing. Ames Research Center. Ames also develops science and technology requirements for current and future flight missions relevant to astrobiology. Moffett Field has been a government airfield since , but was closed as a military base in It is now a shared facility known as Moffett Federal Airfield.
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The instruments were used for mapping the skies extremely accurately. The Sun is at the top of the figure 8 at the summer solstice and at the bottom at the winter solstice. AM Herculis star AM Binary system, with period in the range 1 to 3 hours, that shows strongly variable linear and circular polarization and also eclipses. AM Herculis stars are strongly variable X-ray sources and their lightcurves change from orbit to orbit.
They also show changes in brightness and in variability with time scales of decades. The total range of light variations may reach 4—5 magnitude V. AM Herculis stars seem to be related to DWARF NOVAE, in that one component is a K-M-type dwarf and the other a compact object, but they differ in that the magnetic field of the compact component is sufficiently strong to dominate the mass flow and thus cause the effects observed. Am Herculis stars are also known as Polars. The first Amor-type asteroid to be discovered was EROS, in , but the archetype giving them their collective name is Amor.
That object was found in , the same year as the first Apollo asteroid. Over Amors had been discovered by late This definition is in contrast to the normal usage in physics, where the term is applied to half of the peak-to-peak value assumed by any parameter. Am stars are enriched by factors of 10 or so in copper, zinc, strontium, zirconium, barium and the rare earths, but are depleted in calcium and scandium. As slow rotators that lack outer convection layers, these stars are apparently braked by the gravitational effects of close companions.
In the quiet atmospheres, some atoms fall under the action of gravity, while others rise by means of radiation pressure. Sirius is an Am star. A considerable degree of patience and technical skill is required to record the analemma photographically. They are thought to be fragments of a captured asteroid that subsequently broke apart. Ananke was discovered in by Seth Nicholson. It takes days to orbit Jupiter at an average distance of The population of known outer satellites of Jupiter is increasing rapidly, with eleven more having been discovered since Like other freshly formed impact sites, Anaxagoras is the centre of a bright system of rays and steep, finely terraced walls.
Its rays extend south to Plato. The rims rise to a height of m 10, ft above the floor. To the east, Anaxagoras overlaps Goldschmidt, a degraded ring, 80 km 50 mi in diameter. Anaxagoras of Clazomenae c. He believed it originated as a disk whose rotation caused the matter in it to separate according to its density, the densest materials settling at the centre and the more rarefied materials spreading out towards the periphery.
He was imprisoned for teaching that the Sun was not a deity but a red-hot stone, and that the Moon, the phases of which he correctly explained, shone by reflected sunlight. Anaximander of Miletus c. He taught that Earth moves freely in space — not fixed upon anything solid. He was said to have discovered the equinoxes and the obliquity of the ecliptic, but there is little evidence for this.
Ancient Beijing Observatory Astronomical observatory founded in , situated in central Beijing on an elevated platform 14 m 46 ft above street level. In about , the Flemish Jesuit missionary Ferdinand Verbiest —88 began re-equipping the observatory, and six of the eight large bronze instruments remaining on the site date from The other two were built in and Using this arrangement, Anderson was also able to separate very close double stars.
In mythology, Andromeda, the daughter of King Cepheus and Queen Cassiopeia, was chained to a rock as a sacrifice to the sea monster Cetus and was rescued by Perseus. NGC is an open cluster of several dozen stars fainter than mag. M31 is the nearest spiral to the Milky Way, some 2. Its proximity has led to intensive studies by astronomers, yielding fundamental advances in such diverse fields as star formation, stellar evolution and nucleosynthesis, dark matter, and the distance scale and evolution of the Universe.
The Andromeda spiral is visible to the naked eye. Photographs taken in by Isaac Roberts — using a inch 0. In —24, using the inch 2. Many of the star-like points in this image are in fact globular clusters within its galactic halo. Reflector at the Palomar Observatory, California. This distinction remains in current use and is an essential feature of accepted theories of star formation, and stellar and galaxy evolution. The discovery of the two stellar populations led in turn to a crucial finding for cosmology.
The Cepheid variables turned out to be of two subsets, one belonging to each population, obeying different period-luminosity rules. The gas is distributed in a torus, the innermost parts of which seem to be falling towards the nucleus. Radial velocities of hot gas clouds across the galaxy have been mapped. Together with HI observations, these measurements allow a rotation curve to be constructed as a function of galactic radius. HI measurements, particularly, suggest that the outer regions of M31 contain substantial amounts of unseen additional mass.
This may be the result of a comparatively recent merger between the Andromeda Galaxy and a dwarf companion. The disk of M31 shows a number of star clouds, the most obvious being NGC , which covers an area of. About 30 novae can be detected in M31 each year by large telescopes. It might be expected that the proximity of M31 would mean that it could make a substantial contribution to theories for the development of spiral structure.
Instead, it has contributed controversy, partly because the galaxy is so close to edge-on that details of the spiral structure are hard to delineate. Indeed, it is not even known how many spiral arms there are. Halton ARP has proposed two trailing spiral arms, one of these disturbed by the gravitational pull of M Kalnajs proposes instead a single leading spiral arm, set up via gravitational resonance with M The dust clouds do not help in deciding between these two models.
M31 is surrounded by a halo of globular clusters, which is some three times more extensive than the halo around our Galaxy. The great spread in element abundances in the M31 globular clusters suggests slower and more irregular evolution than has occurred in the Milky Way.
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In some 3 billion years, M31 and the Milky Way will collide and merge eventually to form a giant elliptical galaxy. M31 is our sister galaxy, the nearest spiral galaxy that is similar in most attributes to the Milky Way. Much of our home Galaxy is hidden from our perspective by massive dust clouds; we rely on the Andromeda Galaxy for an understanding of our own Galaxy, as well as of the rest of the Universe. The parent comet split into two fragments in and has not been definitely seen since ; it is now considered defunct. Further displays were seen in , , and , in each case during the first week of December.
When seen in the Andromedids appeared on the last day of November. The NODE, where the orbit of the meteoroid swarm and the orbit of the Earth intersect, is subject to change as a result of gravitational perturbations by the planets. The Andromedid node is moved earlier regresses by two or three weeks per century.
A good, though not spectacular, Andromedid shower was seen on November 30, confirming the prediction. Since the orbital period was about 6. Soon after sunset on November 27, a day earlier than expected, western European observers were treated. The event caused less alarm and terror among the general population than it might have done, there having occurred only six years previously an equally dramatic LEONID display, which had caused no harm. The shower of led, incidentally, to a mysterious episode in astronomical history. The object was observed again the following night, but then clouds intervened and when a clearance finally came, there was no sign of it.
The observations were inadequate for the calculation of an orbit and the prediction of future positions, so the comet, if such it was, was lost. Both alternatives are hard to believe, and the question remains open. The next encounter was badly timed, and no shower was seen. In , two revolutions after the event, European observers were delighted and thrilled by an even greater meteor storm on November 27, during which Andromedid rates were estimated counting was virtually impossible at 75, per hour. This rate compares with that of , per hour estimated for the Leonid peak.
The most intense activity in the Andromedids was over in about six hours such meteor storms are invariably short-lived , though lower rates were detected for a few days to either side. This suggests that the core filament in the Andromedid meteor stream in had a width of about , km , mi. Since the Andromedids have been quite undistinguished, and the shower is now to all intents and purposes defunct.
Planetary perturbations have shifted the orbit of the meteoroid swarm so that it does not at present meet that of the Earth. A fairly strong display occurred on November 23, while on November 24 about Andromedids per hour were seen. A computer model of the Andromedid stream by David Hughes — , of the University of Sheffield, UK, suggests that further planetary gravitational perturbations will bring the shower back to encounter the Earth around The Angara will be based on a first stage, which forms the basic vehicle for flights to low Earth orbit.
This stage can be clustered together with two types of upper stage, forming a more powerful first stage, for flights to geostationary transfer orbit GTO. The largest Angara, with five core first stages and a high-energy KVRD upper stage, will be able to place 6. The AAO operates the 3. Inaugurated in , the 3. AAT remains the largest optical telescope in Australia, although both partner countries now have access to larger southern-hemisphere instruments.
Its IRIS2 infrared imager and 2dF two-degree field system, which allows the spectra of target objects to be obtained simultaneously, provide unique facilities for wide-field observations. Angrites are medium- to coarse-grained basaltic igneous rocks. The angle subtended by an object is determined by its true diameter and its distance from the observer; if the distance to an object is known, its true diameter may be calculated by measuring its apparent diameter.
It is the product of the angular velocity and the moment of inertia I. The moment of inertia is the rotational equivalent of mass, and for a small particle it is given by the mass of that particle multiplied by the square of its distance from the rotational axis. For large objects the overall moment of inertia must be found by adding together the individual moments of inertia of its constituent particles.
Angular momentum is always conserved that is, its total value for the system remains constant during any changes. It was founded c. Today, the observatory is used largely for public outreach, having been restored in as a centre for 19th-century science, technology and culture. This eclipse was photographed on May 10 from Mexico.
Such events, while interesting in their own right, are not generally considered as dramatic as a total solar eclipse, since they do not allow the solar corona and prominences to become visible, or cause a noticeable darkening even at their maximum extent. Equivalent to It can be defined as a true, eccentric or mean anomaly. In the diagram the point X represents the position of the body, and the angle PSX is the true anomaly. The mean anomaly is measured similarly, but to the position of an imaginary body that orbits at constant angular speed with the same period as the real body.
It cannot be indicated by a simple geometrical construction. The eccentric and mean anomalies are intermediate angles used in the calculation of the position of the object in its orbit at any time. The difference between the true and mean anomaly is the equation of the centre. Highland basalts are richer in aluminium and calcium, and poorer in iron, magnesium and titanium, than basalts found in the lunar maria low-lying plains. The antapex lies in the direction of the constellation Columba at around RA 6h dec. It is diametrically opposite on the celestial sphere to the APEX, the direction towards which the Sun and Solar System appear to be moving.
This venue is ideal for astronomers who want to work at infrared, submillimetre and millimetre wavelengths. These portions of the electromagnetic spectrum are compromised by water vapour, which is pervasive at most other locations on Earth and makes observations at these long wavelengths difficult or impossible. But at the pole, the vapour is frozen out, leading to a dark, transparent sky ideal for investigating star-formation processes in molecular clouds and the evolution of protostars and other young objects. Similarly, distant, primeval galaxies can be effectively studied because their visible light has been redshifted to long wavelengths.
In addition, of course, a polar site features a totally dark sky 24 hours a day during midwinter, which allows continual monitoring of targets. Antarctic astronomy was born around , spurred. The principal organization is the Center for Astrophysical Research in Antarctica. Sources of extremely high-energy neutrinos include active galactic nuclei, black holes, supernovae remnants and neutron stars.
There is much more to Antarctic astronomy than what happens at the pole. On the polar plateau in East Antarctica lies Lake Vostok. The size of Lake Ontario in North America, it has been buried under thousands of metres of ice for millions of years.