Shedding Some Light on a Vanishing Star

Shedding Some Light on a Vanishing Star[1]

The ball of glowing gas is a remnant of an explosion that occurred in 1437 and was spotted by astronomers in Korea. The red lines point to the “cataclysmic variable” system that produced an explosion. New research retraces its motion across the sky. Credit K. Ilkiewicz and J. Mikolajewska

Nearly six centuries ago, Korean astronomers scanning the night sky for omens of the future spotted a new star in the cluster of stars they called Wei, and what today’s star watchers consider the tail of the Scorpius constellation.

Fourteen nights later, it vanished.

Astronomers have now identified the source of that brief brightening—a binary star system a couple of thousand light-years away.

Michael Shara, an astrophysicist at the American Museum of Natural History in New York, has been seeking to understand what happens following explosions in violent star systems known as “cataclysmic variables.” He has searched for the remnants of this particular event for a long time.

“Now, about 25 years later, we’ve finally come up with it,” Dr. Shara said. The researchers report their findings August 30, 2017 in the journal Nature.

In these systems, one of the stars is a white dwarf, the burned out but still hot remnant of a star. The powerful gravity of the white dwarf pulls hydrogen away from its companion star and onto its surface. “You accumulate about a Pacific Ocean’s worth of hydrogen,” Dr. Shara said.

A series of photographic plates spanning six weeks in 1942 shows the old nova of 1437 undergoing a dwarf nova eruption. Credit Digital Access to a Sky Century @ Harvard

With more and more hydrogen, the pressure builds until it sets off a thermonuclear explosion, a burst of light known as a nova that is up a million times as bright as the Sun.

“You get a giant fusion bomb, a hydrogen bomb going off on top of this white dwarf star,” Dr. Shara said.

That is what the Koreans saw on March 11, 1437.

As powerful as nova explosions are, they do not destroy either star (unlike much larger supernovae). The white dwarf fades, and the cycle repeats until the next explosion, which could be up to 100,000 years later.

In recent decades, astronomers have observed the fading of novae over decades. They have also spotted similar binary star systems that appear quite stable, calmly orbiting each other, and others that are belching only small eruptions known as dwarf novae.

Three decades ago, Dr. Shara proposed that all three types—novae, dwarf novae, and the quiescent binaries—were variants of the same type of system but at different stages. The idea was hard to test because astronomers have not been observing them for very long.

Thus, historical novae like the one observed in Korea could provide important clues to the life cycle between explosions. For years, he and colleagues looked for the 1437 nova without success. Recently, they expanded the field of search and came across a promising cloud of gas, or nebula, that looked like the carcass of a nova. Other astronomers had noted this previously, but, puzzlingly, the star at the center of the nebula is not a cataclysmic variable.

A point of light not far from the center, however, is indeed a cataclysmic variable. (The white dwarf and its companion are so close together that they appear as a single star in photographic plates.)

That, the astronomers thought, could have been the source of the nova.

They scoured the astronomical archives of Harvard, discovering a picture of the same star in 1923. That allowed them to see how far the off-center point of light had moved across the sky over the past century. Then they traced it back to where it would have been in 1437—smack at the center of the nebula. (The star that currently appears to be at the center just happens to be along the line of sight and is unrelated to the explosion.)

“The real novelty here is we have a clock,” Dr. Shara said. “We can see how fast it’s moving across the sky.”

Additional Harvard images of the same star in the 1940s showed modest changes in brightness—dwarf nova eruptions. That supports Dr. Shara’s hypothesis that these types of star systems go through all three stages.

In an accompanying commentary in Nature, Steven N. Shore, a professor at the University of Pisa in Italy who was not involved with the research, described the work as “a lovely piece of historical scholarship.”

Dr. Shore said it was too early to tell whether this cataclysmic variable is typical or unusual, but it provides a long series of data for astrophysicists to try to recreate with computer models.

[1] Kenneth Chang, “Casting Light on Mystery of a Star That Vanished after 14 Days,” New York Times (Aug 30, 2017). A version of this article appears in print on September 5, 2017, on Page D2 of the New York edition with the headline: “Solar Mystery: Shedding Some Light On a Vanishing Star”.

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Expansion Explained

Expansion Explained[1]

Q: How did astronomers discover that the expansion of the universe was accelerating?

(A question from Steve Ciucci, Madison, Wisconsin)

A: In the early 1990s, two teams of astronomers set out to measure the universe’s expansion history to predict its future. If the universal expansion was slowing down a lot, it would someday stop and reverse itself, ending in a hot Big Crunch. If, instead, the deceleration was small, the universe would expand forever (albeit at a decelerating rate).

Each of these possibilities predicted a different relationship between the distances (or, more precisely, “lookback times”) of galaxies and their redshifts (the amount the universe had stretched while the light was on its way to us).

Redshifts are easy to measure from spectra of galaxies, except when the galaxies are faint. Astronomers obtain distances of nearby galaxies by finding a star of known luminosity (power, or absolute magnitude), measuring its apparent brightness (apparent magnitude), and applying the inverse-square law of light. But at great distances, normal stars can’t be seen, so the astronomers used Type Ia supernovae—exploding stars resulting from white dwarfs that approach their maximum possible mass (the Chandrasekhar limit). These can be billions of times as powerful as the Sun, and their peak luminosities are nearly uniform.

The two teams used large telescopes to take deep images of various parts of the sky, repeating these same fields a few weeks later. They found supernova candidates among the thousands of faint galaxies. They then obtained spectra of the candidates to confirm that they were Type Ia supernovae and to obtain their redshifts. By repeatedly imaging these supernovae, they measured their light curves and peak brightnesses. The teams also took issues into account such as the nonuniformity of Type Ia supernovae, the presence of intervening dust, and possible cosmic evolution of supernovae.

The result was that the supernovae were too faint (for a given redshift) to be consistent with decelerating or constant-speed expansion of the universe. Instead, the data implied that the expansion has been accelerating in the past 5 billion years. (Later measurements revealed the era of deceleration during the first 9 billion years.) Other techniques have now confirmed this acceleration, which most astrophysicists attribute to the presence of dark energy of unknown origin.

[1] From AskAstro (Alex Fillppenko, (Professor of Astronomy, University of California, Berkeley, CA), in Astronomy (44, 6, April 2016, p. 34)

Three “Capital” Stars

Three “Capital” Stars?[1]

Did the positions of bright stars, Regulus, Spica, and Arcturus, have anything to do with inspiring Benjamin Banneker to envision a layout for Washington?

Two hundred and twenty-five years ago, Benjamin Banneker, a self-taught astronomer and mathematician from Baltimore County, Maryland, helped survey the boundaries of our nation’s capital using the stars as guides. Over the years, a rash of books has flavored this episode in American history with sprinkles of the occult, including sacred alignments of key structures with bright stars. But critics have picked apart many of these claims like crows on roadkill.

Indeed, American historian Silvio Bedini, who wrote the definitive biography of Banneker, notes that “considerable confusion” exists among writers concerning Banneker’s role in the survey of our federal city. Nevertheless, we can still look to the stars this month and imagine something “capital” about them.

Banneker’s role

Banneker’s assignment was to assist Maj. Andrew Ellicott, whom President George Washington appointed as the head of a six-man team. First observations commenced February 11, 1791, and Banneker was the principal observer. Ellicott tasked him mainly with determining the starting point of the survey and maintaining a dock that could relate points on the ground to the positions of the stars at specified times.

Banneker made observations of “about a half-dozen different stars crossing the meridian at different times during the night, and the observations were repeated a number of times,” Bedini says.

Exposure to inclement weather, especially the cold, took its toIl on 60-year-old Banneker, who often would stay up all night, making observations—until he fell ill and returned home probably in late April 1791.

Triple threat

A parade of bright stars crossed the south meridian during Banneker’s stay, including Regulus (Alpha La] Leonis), Spica (Alpha Virginis), and Arcturus (Alpha Boat’s). According to David Ovason, author of Lost Symbols? The Secrets of Washington DC, this seems “to reflect the central triangle in the plan of Washington, D.C.” (the Capitol Building, the White House, and the Washington Monument).

Alas, none of these stars passes directly over the city at any time, and not any of Ovason’s suggested celestial and terrestrial triangles match up upon projection. Still, people wonder if Banneker saw these three stars as fitting symbols of our nation’s capital. Could anything have fueled his imagination?

Capital triangle?

Nicolas Copernicus named Regulus (the Little King) from the belief that it “ruled the affairs of the heavens”—a fitting symbol, as our nation’s government has political authority to rule over the actions and affairs of the people. Regulus also leads Arcturus and Spica across the heavens. Arcturus (the Bear’s Guard) escorts.the Great Bear around the North Celestial Pole. This might symbolize the flow of cosmic justice throughout the night, just as our government keeps watch over its flock and reigns supremely over any injustice. And finally, there’s Spica (Ear of Grain), a just symbol of our nation’s health (amber waves of grain).

Banneker’s attention could have been draft to this trio of stars by Jupiter, which lay about midway along a line between Regulus and Spica in Virgo, whom we see in a classical dress holding an ear of grain. I mention the description of Virgo because the original design of the Statue of Freedom atop the Capitol Building was a female in a classical dress holding an ear of wheat.

So rather than trying to force stars onto Earth, all one has to do in April is look east around 9 P.M. and see the three capital stars that Banneker must have seen (if not measured and identified) in his nightly transit surveys of our nation’s capital.

[1] From an article by Stephen James O’Meara, “Three ‘Capital’ Stars’”, Astronomy (44, 4, p. 18)

1986 The Challenger Disaster

Space exploration stumbled to a devastating halt when the shuttle Challenger exploded just 73 seconds after launch on January 28, resulting in a total loss of ship and crew, The shuttle carries five astronauts and two payload specialists, including high School teacher Christa McAuliffe. Engineers voiced concerns about the potential dangers of the cold temperatures on launch day on the shuttle’s rubber O-rings, but a flawed chain of decision-making failed to prevent catastrophe. NASA spent months investigating its mistakes, and years trying to learn from them. President Ronald Reagan addressed the nation that night while the country and the world mourned Challenger’s loss: “We’ve grown used to wonders in this century. It’s hard to dazzle us…. We’ve grown used to the idea of space, and perhaps Ike forget that we’ve only just begun. Were still pioneers”

It took nearly three years for NASA to return to human space flight.

Cosmic Surprises Keep Blowing Our Minds

Cosmic Surprises Keep Blowing Our Minds[1]

Some areas of science advance in increments. We see slow evolutionary improvements in aeronautical engineering and medical discoveries. But astronomy is different. Here, the universe often leaps out and goes boo! Although we are far from it, let’s use April Fool’s Day as our excuse to review the top 20 pranks” the cosmos has sprung on us.

Start with Galileo. Since no one had pointed a telescope at the sky before, he was bound to get surprises. Nobody had foreseen lunar craters or moons going around other planets like Jupiter, as he observed. But when he looked at Saturn, he entered the Twilight Zone. On Earth, there’s no example of a ball surrounded by unattached rings. This was beyond human experience. No wonder it took two centuries for anyone to deduce that they’re neither solid nor gaseous, but made of separate moonlets. So our first April Fool’s prank? Saturn’s glorious rings.

Fast forward to 1781. That’s when William Herschel first peered at a bizarre green ball. No one had discovered any planets beyond the five bright ones since prehistory. No great thinker, no holy book, no philosopher had done more than idly speculate about more planets out there in our Solar System. Herschel’s spotting of Uranus was the most unexpected and amazing discovery all time.

Surprise No. 3 stays with Herschel. Nineteen years after finding Uranus, he discovered the first-ever invisible light. Light we cannot see?

It astonished the world. The bulk of the Sun’s emissions are invisible “calorific rays.” Late that century, people started calling it infrared.

We have to credit Albert Einstein with several mind-blowers. First, that space and time both shrink or grow depending on the observer’s conditions. This means the universe does not have a fixed size. And a million years elapse in one place while a single second is experienced by someone else—at the same time. Did anyone see that coming? Do most people grasp this even today? As if that wasn’t enough mind twisting, he showed that solid objects and energy are two faces of the same entity.

Jump ahead to 1920. That’s when Arthur Eddington figured out what makes the stars shine. Imagine: a new type of “burning.” An alchemic change of one element to another. This nuclear fusion process is so efficient that each second the Sun emits the energy of 96 billion 1-megaton H-bombs. Sure, physicists knew the Sun couldn’t create light and heat by burning in the usual way. But this?

A few years later, Edwin Hubble announced that all those spiral nebulae were separate “island universes.” Granted, this had been suspected by half of all astronomers for decades. It was not a sudden April Fool’s. Still, bam, the universe officially became unspeakably larger than it was before. That’s gotta count as a boo! event.

Then the quantum gang rode into town. Their revelations were astonishing. Empty space seethes with energy. A bit of matter can know what another is doing and react instantaneously across the universe as if no space exists between them. An observer’s presence influences the experiment.

In 1930 came the prediction for a new tiny entity, the neutrino. It’s the universe’s most common particle. Five trillion zoom through your tongue every second. The 1936 discovery of the subatomic muon was equally unexpected. It famously made Nobel Prize winner Isidor Rabi say, “Who ordered that?”

The 1967 discovery of the first neutron star revealed—a sun smaller than Hawaii, whose material is so dense that each speck equals a cruise ship crushed down to the size of the tip of a ballpoint pen. And that was a double whammy because it was also the first pulsar. Did any genius foresee that some stars could spin hundreds of times a second?

The surprises haven’t let up. A microwave background energy filling all space? A solid Pluto-size ball in the middle of our planet, spinning faster than the rest of Earth? And what about the enormous hexagon at Saturn’s north pole? Or the fact that cosmic “rays” are overwhelmingly protons?

1998 brought astronomers another stunner. When the universe was half its present age, all its galaxy clusters simultaneously started moving faster. It’s as if stupendous rocket engines fired simultaneously everywhere in the cosmos. We don’t know anything about this antigravity force—but we now call it dark energy.

Then in 2010, the Fermi gamma ray telescope found two ultra high-energy spheres, each 25,000 light-years across, occupying half of our southern sky. The entities meet tangentially at our galaxy’s core like an hourglass. They’re violent and utterly baffling.

We’re out of room, but the universe never is. For the cosmos—and we who explore it—it’s always April Fool’s.

[1] Derived from an article by Bob Berman, “April Fool’s!” in Astronomy (44, 6, April 2016, p. 10)

Meteor Impact Structures

September 1-5, 2017 I spent in the Big Bend area. The geology of Big Bend represents almost every geomorph known. But far less known, West Texas is home to the only two meteorite impact structures on the surface of Texas: Odessa Meteor Craters and the Sierra Madera Astrobleme. The Sierra Madera Astrobleme is a significant surface feature in the Big Bend area.[1]

An “astrobleme” (literally “star wound”) is a scar left from a meteorite impact. A more general term, impact structure, is closely related to the terms impact crater and meteorite impact crater, and is used in cases in which erosion or burial has destroyed or masked the original topographic feature with which one normally associates the term crater. This is the fate of almost all old impact craters on Earth, unlike the ancient pristine craters preserved on the Moon and other geologically inactive rocky bodies with old surfaces in the Solar System. Impact structure is synonymous with the less commonly used term astrobleme.

In an astrobleme, the typical visible and topographic expressions of an impact crater are no longer obvious. Any meteorite fragments that may once have been present would be long since eroded away. Possible impact structures may be initially recognized by their anomalous geological character or geophysical expression. These may still be confirmed as impact structures by the presence of shocked minerals (particularly shocked quartz), shatter cones, geochemical evidence of extraterrestrial material or other methods.

Both have been studied in detail by scientists. Odessa is credited as being only the second meteor crater to be recognized on our planet and is designated a “National Natural Landmark.” Sierra Madera was extensively studied by NASA geologists as a probable analogue for the lunar crater Copernicus.

The main Odessa crater is 0.17 km in diameter whereas the Sierra Madera crater is nearly 70 times larger at 12 km in diameter. At least four small craters are associated with the main Odessa Crater. Indeed, it has been proposed that Meteor Crater, Arizona may have been part of the same fall as the Odessa meteorites 50,000 years ago.

Two types of craters are recognized on Earth; and we have excellent examples of both here in West Texas. The main Odessa crater is used as the type example for simple craters. Indeed, craters around the world are classified as either the “Odessa type” or the “Barringer type” (Meteor Crater, Arizona).

Sierra Madera Astrobleme

Sierra Madera is characterized by astrogeologists as the best exposure of a complex crater. It is located south of Fort Stockton, and is crossed by US385. Seventy years ago the renowned geologist P. B. King recognized that the Sierra Madera structure was a different breed of cat. The circular cluster of hills is 1.5 miles in diameter. Older strata are exposed in the central part and strata generally dip radially away from the center. Permian rocks are uplifted as much as 4000 feet in the central uplift. Cretaceous rocks dip gently away from the central uplift and form the outer rim of the structure. However, it is not a simple, structural dome because the bedding is also highly folded and faulted on the small scale.

Many domal structures to the south have igneous rocks associated with them, but Sierra Madera does not. Oil companies are attracted to structural domes, or “four ways of dip,” and Sierra Madera was no exception. Drilling revealed an amazing phenomenon – at deeper levels the dome did not exist!

Robert Dietz suggested that the Sierra Madera structure might be the result of a meteorite impact. Howard Wilshire studied the area and showed that shatter cones and micro-breccias indicated extremely high pressures of 200 kilobars. Wilshire’s work convinced most geologists that the impact of an extraterrestrial body created a circular crater 6 miles in diameter and a central uplift caused by impact rebound.

 

 

 

 

 

 

 

 

Digital Elevation Model (DEM) of Sierra Madera impact structure showing central mountains and raised rim (red outline). Diameter of rim is 6 miles. Crest of the Central Uplift is 4583’ above sea level.  DEM compiled by Matthews from four 7.5’ quadrangles


View northward from the rim of the Sierra Madera Crater. Strata of the central uplift were raised 4000 feet from rebound caused by the impact.


Cross section illustrating how only the upper strata were disturbed by the impact (from Wilshire, 1972).

SELECTED BIBLIOGRAPHY

Wilshire, H.G., Offield, T.W., Howard, K.A., and Cummings, D., 1972, Geology of the sierra madera Cryptoexplosion structure, Pecos county, Texas: U.S. Geological Survey Professional Paper 599H, 42 p.

[1] See Meteor Impact Structures, accessed November 29, 2017 at https://www.utpb.edu/ceed/geology-resources/west-texas-geology/meteor-impact-structures

A Lifetime of Astronomy

A Lifetime of Astronomy[1]

My 79th birthday was September 5, 2017. I am privileged to have had his many years. I have seen some remarkable things in science in my years, among the most impressive have been the growth of astronomy. Astronomy grew more in the last 75 years than in all prior history.

For my 79th birthday, here are some of the milestones in astronomy. We begin.

 

 

 

 

 

The 1940s: The 200-Inch Hale Telescope

The things that are most vivid to me about the ‘40s is World War II. The entire culture was dominated by Pearl Harbor, the war in Europe, the war against the Japanese, workers at home (my mother worked in an ordnance factory), returning service men, and finally the end of rationing.

It is not given to us to know the fruits of what we do. So we must do them on faith, because good works occasionally pay off far beyond sight. If, in the 1930s and ‘40s, Charlie and Helen Federer hadn’t taken one risky leap in life after another for the advancement of amateur astronomy and the popularization of science, the hobby and perhaps scientific literacy in America would not have grown as well as they did. Perhaps your own life would be less.

In 1937 Grote Reber, an amateur astronomer and ham radio tinkerer, built the world’s second radio telescope and the first that you’d recognize as such today. He hand-shaped its 31-foot paraboloidal dish and was the world’s only radio astronomer for nearly a decade. Reber carried out an all-sky survey at 160 megahertz one big pixel at a time (after getting poor results at higher frequencies) and published many results in the early 1940s.

When astronomers dedicated the Hale 200-inch telescope in 1948, the public was probably as excited as it was by the launch of the Hubble Space Telescope in 1990. A postage stamp honored the occasion.

Dipping elsewhere into the 1940s, scientific thought also focused on whether Mars is inhabited (conclusion: “we just do not know”). Another new and exciting: “Radar and Radio in Astronomy.” To many amateurs the concept of radio astronomy was new. Astronomy had always been about the narrow little bit of the spectrum spanning visible light, with slight extensions into the infrared and ultraviolet. But now, radio “noise of cosmic origin promises to become a fact-finder on Milky Way structure.” In the decades to follow, people interested in astronomy had front-row seats on the slow opening of the entire electromagnetic spectrum to astronomy—bit by bit, here and there, from radio to the highest-energy gamma rays—something the current generation of astronomers takes for granted.

However, at the end of the 1940s the decade’s biggest astronomical development would surely have named the brand-new, 200-inch (5-meter) Hale telescope on Palomar Mountain (pictured above). It had twice the aperture of the world’s previous largest telescope (Mount Wilson’s 100-inch, dating from 1919), and it would hold the title until 1975.

The 1950s: Dawn of the Space Age

In the 1950s I began high school. My fascination with science blossomed. Although I had the worst possible physics teacher in the world, I did learn something. Math was my forte in HS.

With World War II over and America testing and improving upon captured German V2 rockets (the source of science fiction’s iconic image of the finned rocket ship), a Space Age actually seemed within reach—at least to readers of literature like Willy Ley’s The Conquest of Space (1951). Extensive reporting in newspapers and magazines covered rocketry and spaceflight planning.

The rest of the world suddenly awoke to the Space Age on October 4, 1957, when the Soviet Union launched the first artificial satellite, Sputnik 1. Now in college, I sat at the short wave radio in the college’s electronics lab and was able to detect the beep, beep, beep of Sputnik as it passed overhead.

Fred Whipple at Harvard Observatory, had already organized Operation Moon-watch worldwide. The program called for rows of observers with special wide-field telescopes to create “picket fences” of overlapping fields of view, to detect and record the paths of any orbiting

Large commercial telescopes were still too expensive for most people to afford. The amateur telescope making movement, led by Scientific American and Sky and Telescope, democratized astronomy, drove down prices, and trained up the people who founded and staffed many of the telescope companies that we buy from today.

The 1960s: To the Moon!

The 1960s will forever be known as when America landed the first humans on another world. On July 20, 1969, as Apollo 11 astronauts Neil Armstrong and Buzz Aldrin prepared to step out of their Lander, the science-fiction writer Robert A. Heinlein declared to CBS News anchorman Walter Cronkite, “This is the greatest event in all the history of the human race, up to this time. Today is New Year’s Day of the Year One. If we don’t change the calendar, historians will do so. This is our change … from infancy to adulthood of the human race.”

Nope. For one thing, humans haven’t again ventured beyond low Earth orbit since 1972. But it was a time when all sorts of great possibilities seemed near at hand. In 1960, Frank Drake turned centuries of speculation about civilizations among the stars into a scientific endeavor with his Drake Equation and Project Ozma, the world’s first serious first serious SETI experiment. The Drake equation was proposed by Dr. Frank Drake, explaining his ideas before practically anyone else. We saw the birth of x-ray astronomy, the detection of neutrinos from the Sun’s core, and the discovery that mysterious quasi-stellar radio sources, QSRS or “quasars,” had redshifts that placed them at fantastic distances, meaning they had to be fantastically powerful. We also learned about the discovery of pulsars and had advance notice of the Leonid meteor storm of 1966.

I was a physics graduate student in the early ‘60s. One of my fellow grad students had made his own telescope while in college. I can’t imagine the precision he had to achieve to have a good ‘scope. I was at the University of Kansas Department of Physics and Astronomy. We had a pretty good telescope and observatory there.

Arno Penzias and Robert Wilson stand under the Bell Laboratories Holmdel horn antenna (fully rotatable), with which they accidentally discovered the all-sky afterglow of the Big Bang.

In an even greater turning point, we learned that Arno Penzias and Robert Wilson had discovered a cosmic hiss of microwave radiation emanating from the entire celestial sphere. This was the predicted, brilliant white-light afterglow of the Big Bang itself, redshifted by a factor of 1,100 to microwave wavelengths by the subsequent expansion of space. The discovery tipped the scientific consensus into accepting that the universe truly had a Big Bang origin at a particular moment in time.

 

The 1970s: Black Holes

I spent the last part of the 1960s in the Army as an intelligence analyst. My focus was on Missiles and Space, and nuclear weapons. I left the Army and worked for a time at Exxon Production Research. Finally I went back to academia and began my long career at Rochester (NY) Institute of Technology.

Human exploration of space, in this decade, dwindled in part because machines, expendable and far more economical, proved so good at it. In the 1970s and 1980s, we followed Mariner flybys of Mars, Mariner 10 unveiling Mercury, the Soviet Union’s Venera landings on Venus, and the long, epic missions of Voyagers 1 and 2 to Jupiter, Saturn, Uranus, and Neptune and their systems of moons.

The astronomical high note of the 1970s has to be the first successful Mars landers, NASA’s Vikings 1 and 2, in the summer of 1976. After a lifetime of intense public yearning to know what Mars was really like, we saw the answer: barren deserts of rock and dust with no discernible trace of life, much less Martians. Once and for all the world grasped that we’re alone in the Solar System, and that there’s no decent real estate beyond Earth.

Every era has its particular astronomical fascination, and in the 1970s it was black holes. Physicists had only recently come around to the idea that such things could be physically real, rather than irrelevant mathematical quirks of Einstein’s equations. In 1971 astronomers noted rapid x-ray variability in Cygnus X-1, a sign that extremely hot matter was cramming down onto an extremely small object. The tiny object was so massive, judging by its orbital effect on its giant companion star, that only a black hole would fit the bill. X-ray astronomers turned up more such systems that seemed to include “stellar mass” black holes. Others realized that matter accreting onto “supermassive” black holes offered the best solution to the mystery of quasars and active galactic nuclei.

A quirky visionary named John Dobson broke the rules of telescope making to popularize giant scopes on cheap, boxy altazimuth mounts: the Dobsonian reflector. He and his friends originally built them to show off the heavens to people in the sidewalks and parks of San Francisco. Dobsonians became hugely popular, and their large apertures opened up amateur deep-sky observing to a new degree. The 1970s also saw the popularization of the compact Schmidt-Cassegrain telescope, which quickly became as emblematic of the hobby as the refractor and reflector. To accompany the big new scopes, Burnham’s Celestial Handbook to the deep sky appeared in installments and became a universal must-have.

In the winter of 1976, Comet West [orbital path shown in the figure at the left] lit the morning sky.

Pluto’s big moon and the rings of Uranus were observed. Cosmic gamma-ray bursts, first detected by satellites watching for nuclear weapons tests, became an intractable, but dearly important, puzzle. A binary pulsar losing orbital energy indirectly proved the existence of gravitational waves, another triumph for general relativity. The nature of the dark matter showing its influence all over the cosmos became a top problem. And in 1975, a network of clubs began the public-outreach tradition of Astronomy Day.

The 1980s: Halley

I continued my academic career at RIT, frequently attending astronomy colloquia at the University of Rochester.

Public interest in astronomy took a permanent leap forward in 1980 with Carl Sagan’s hit series Cosmos on public television. Less visibly, physicist Alan Guth that year had his “spectacular revelation” of how the Big Bang likely worked—whereby known physics could account for the eruption of everything from essentially nothing and explain several other “impossible” features of today’s cosmos all at once. A new term, multiverse, emerged to describe the vastly larger ensemble of separate universes, now disconnected from ours, that the theory seemed to imply.

The first Space Shuttle, Columbia, launched in 1981. Challenger blew up in 1986. Halley’s Comet, anticipated by everyone who’d had even a passing interest in astronomy since 1910, proved in 1985 and 1986 to be the distant, poorly placed dud that we had more or less predicted. At least our skilled chart-users could find it with their scopes to show to a disappointed public.

In February 1987, Supernova 1987A in the Large Magellanic Cloud erupted to magnitude 2.9; it was the closest and brightest supernova seen since before the invention of the telescope. A 13-second burst of neutrinos, detected at several places around the globe right about when the explosion should have initiated, confirmed that Type II supernovae result from the sudden collapse of a massive star’s core.

The Very Large Array in New Mexico began full operation in 1980, opening today’s era of high-resolution, multi-dish radio astronomy. The Dobsonian revolution continued to spread among amateurs. The price of large amateur scopes kept declining in real terms, undercutting amateur telescope making but rendering the hobby ever more accessible.

Alarmists predicted the iminent end of amateur astronomy if light pollution continued to worsen at the rate it was doing. But for the first time, night-sky enthusiasts began gaining the knowledge and organization to do more than writing harangues  about it. In Tucson, Arizona, astronomers at Kitt Peak National Observatory met with startling success in getting the city to reduce its waste light beaming sideways and upward. This effort led to the founding of the International Dark-Sky Association in 1988. It’s hard to remember back when the fight was hopeless, when most people ridiculed the notion of “light pollution,” and when no one had heard of full-cutoff shielding for outdoor fixtures.

The 1990s: Hubble

By 1996 I decided to leave RIT, and retired as Professor Emeritus. We moved to San Angelo to be away from snow and near family. In a few months I was working again, full time, at Angelo State University.

The long-anticipated, long-delayed Hubble Space Telescope finally launched in 1990. Our elation turned to horror when, once opened to the stars, its main mirror immediately proved to have been shaped to the wrong figure. The error was so gross that an amateur telescope maker could have spotted it with a homemade Foucault tester set up on a stepladder aimed at the mirror during the time it was in storage.

The New York State Section of the American Physical Society met in Rochester where we had a speaker from Kodak: the man responsible for “fixing” the Hubble. A technician had misused an instrument, making the Hubble nearly blind.

Not for three years were astronauts able to install corrective lenses near the focal plane to allow the Hubble to see as well as designed. Today, after many other upgrades by visiting Space Shuttle crews and 23 years of spectacular productivity, the primary-mirror catastrophe is all but forgotten.

 

The 1993 repair mission was done just in time for Hubble to follow the fragments of Comet Shoemaker-Levy 9 as they dramatically dove into Jupiter in July 1994, one by one for several days. The impacts left such big, dark marks on Jupiter’s cloudtops that you could see them with a 2.6-inch telescope, despite Jupiter’s low altitude after dusk. The event dramatized the possibil-ity of devastating impacts in today’s solar system. It also revealed the power of the new World Wide Web. For the first time, many of our readers followed the news and pictures on screens rather than on paper.

We had all grown up being taught that the stars are so far away that we could never find any planets they might have. The abundance or scarcity of planets in the universe was one of the greatest unknowns of astronomy. Then in November 1995 came news that a European team had found a giant planet closely orbiting 51 Pegasi, a humdrum Sun-like star just west of the Great Square of Pegasus. They used spectroscopy to track the star’s slight radial-velocity wobble induced by the orbiting planet. Teams raced to compete with this new method, and “extrasolar planets” became a new field of astronomy almost overnight. Today at least 3,493 exoplanets are confirmed, and many more prospects seem likely to be real. The resulting statistics have answered the age-old question: Most stars have planets.

The title of “world’s largest telescope” passed to the twin 10-meter Kecks atop Mauna Kea in Hawai’i, the first large telescopes with segmented mirrors. And two great comets finally made up for the disappointment of Halley. The eerie, green-headed, gas-rich Comet Hyakutake (C/1996 B2) whizzed close by Earth in the spring of 1996, with its long, straight gas tail spanning much of the sky for a few nights. The next spring Comet Hale-Bopp shone in the west after dusk, the classic portrait of a bright comet with a curved, dust-rich tail.

The 2000s Precision Cosmology

The exploration of the solar system continued with Mars orbiters and rovers, missions to asteroids and Comet Tempel 1, Messenger unveiling more of Mercury, and Cassini taking up orbit around Saturn. Cassini’s hitchhiking Huygens lander descended through the thick hazes of Titan to find a landscape of riverbeds and methane mudflats. Among Cassini’s many other revelations (which continue today), some of the most outstanding are Titan’s weather cycle and great polar lakes of methane (liquified natural gas), water-powered geysers spraying out of Enceladus, and the ongoing dynamical intricacies among Saturn’s rings.

Astronomers started discovering large Kuiper Belt objects, including an especially big one, Eris, that prompted the 2006 demotion of Pluto to dwarf-planet-hood. Regarding a supermassive black hole in the center of our own Milky Way, we declared “case closed”; no other explanation remained possible for what was going on there.

In 2003, Columbia disintegrated with the loss of all on board. The Kepler space observatory launched in 2009, beginning the second wave of exoplanet discovery and analysis—based not on radial-velocity wobbles, but on transits of luckily aligned planets across their stars.

On the grandest scale of all, the 2000s were when “precision cosmology” came of age. NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) mapped the afterglow of the Big Bang well enough that cosmologists could finally pin down key cosmic parameters with high accuracy. For instance, the Big Bang happened 13.8 billion years ago. Everything about the universe—including the origin of galaxies, galaxy clusters, and the largest cosmic structures of galaxy strings and walls—proved to be an essentially perfect match for the inflation process behind the Big Bang. As most recently refined, the cosmos consists of 4.9% normal matter (stuff made of atoms and atomic particles), 26% dark matter made of something else unknown, and 69% “dark energy,” the whimsical name given to a completely inexplicable property of space itself that’s causing the expansion of the universe to speed up. Coincidentally, the expansion speedup had already just been discovered, totally unexpectedly, in 1998.

Add it all up and it comes to just the right total density of matter plus energy—to about 0.5% accuracy at this point—to render space flat and infinite, as predicted by the inflation theory. This, in turn, has made the issue of a multiverse, something thoroughly outlandish to many scientists, more pressing.

 

The 2010s: What Next? Start here

So far, the new decade of S&T has seen Messenger take up orbit around Mercury, Dawn orbit the big asteroid Vesta and then move on to Ceres, the Curiosity rover crawl up the slopes of Mount Sharp on Mars, and, just
this July [2017], Juno reach Jupiter orbit. Voyager 1, at more than twice the distance of Pluto, finally left the solar system’s heliosphere of solar wind and entered true interstellar space.

The European Space Agency’s Planck mission, successor to WMAP, refined precision cosmology and, unexpectedly, played a key role in astronomy’s biggest goof in a very long while. In March 2014 a team based at Harvard announced that their experiment at the South Pole, known as BICEP-2, had found the Holy Grail of cosmic microwave background studies. Slight patterns of polarization in the microwaves, they announced, seemed to be relics of the instant of Big Bang inflation itself—patterning the sky with fantastically magnified images of individual gravitons seen some 10-35 second after our Big Bang budded off from… what? Perhaps an eternally inflating, superdense matrix that exists outside, spawning multiverses. This would have been inflation’s smoking-gun proof.

Alas, the team had relied on a map displayed at a conference by the competing Planck team, which seemed to show that the part of the sky the BICEP team was watching had no foreground dust to mimic the polarization signal. They’d misinterpreted the Planck map; dust was indeed present and could account for the entire observed signal, So it was back to square one. Deeper and better searches for the polarized inflation signal are under way.

New Horizons flew past Pluto and its bevy of moons on July 14, 2015, returning images of an inexplicably active world, with young, craterless plains of soft nitrogen ice, nitrogen glaciers, and signs of a thick atmosphere in the recent past. Little Pluto, the non-planet, was getting the last laugh.

And in the 100th anniversary year of general relativity, LIGO caught gravitational waves from the merger of two black holes far across the universe. The new field of gravitational-wave astronomy promises a bright future.

What unexpected cosmic revelations will the rest of the decade, and the century, bring? We don’t know, but we will, no doubt, be surprised by them. We might even have to revise some theories.

 

[1] This is based on an article by Alan MacRobert, “A Lifetime of Science and Sky Watching,” Sky and Telescope (132, 5, November 2016, pp. 28-35)

The 2010s: What Next?

So far, the new decade of S&T has seen Messenger take up orbit around Mercury, Dawn orbit the big asteroid Vesta and then move on to Ceres, the Curiosity rover crawl up the slopes of Mount Sharp on Mars, and, just
this July [2017], Juno reach Jupiter orbit. Voyager 1, at more than twice the distance of Pluto, finally left the solar system’s heliosphere of solar wind and entered true interstellar space.

The European Space Agency’s Planck mission, successor to WMAP, refined precision cosmology and, unexpectedly, played a key role in astronomy’s biggest goof in a very long while. In March 2014 a team based at Harvard announced that their experiment at the South Pole, known as BICEP-2, had found the Holy Grail of cosmic microwave background studies. Slight patterns of polarization in the microwaves, they announced, seemed to be relics of the instant of Big Bang inflation itself—patterning the sky with fantastically magnified images of individual gravitons seen some 10-35 second after our Big Bang budded off from… what? Perhaps an eternally inflating, superdense matrix that exists outside, spawning multiverses. This would have been inflation’s smoking-gun proof.

Alas, the team had relied on a map displayed at a conference by the competing Planck team, which seemed to show that the part of the sky the BICEP team was watching had no foreground dust to mimic the polarization signal. They’d misinterpreted the Planck map; dust was indeed present and could account for the entire observed signal, So it was back to square one. Deeper and better searches for the polarized inflation signal are under way.

New Horizons flew past Pluto and its bevy of moons on July 14, 2015, returning images of an inexplicably active world, with young, craterless plains of soft nitrogen ice, nitrogen glaciers, and signs of a thick atmosphere in the recent past. Little Pluto, the non-planet, was getting the last laugh.

And in the 100th anniversary year of general relativity, LIGO caught gravitational waves from the merger of two black holes far across the universe. The new field of gravitational-wave astronomy promises a bright future.

What unexpected cosmic revelations will the rest of the decade, and the century, bring? We don’t know, but we will, no doubt, be surprised by them. We might even have to revise some theories.

 

[1] This is based on an article by Alan MacRobert, “A Lifetime of Science and Sky Watching,” Sky and Telescope (132, 5, November 2016, pp. 28-35)