Buran

Due to concerns about the potential military applications of the American Space Shuttle program, the Soviet Union developed a reusable spaceplane during the 1970s and '80s with similar capabilities. The program was called Buran, Russian for "Snowstorm," and you can read more about it here:
Buran

At one time the Space Shuttle was intended to replace every expendable launch vehicle in the United States' rocket stable and perform every government satellite launch by the time it was up to its full launch cadence. To handle the traffic, three launch pads were prepared: two at the Kennedy Space Center in Florida to handle eastbound launches to geosynchronous orbit and other low-inclination orbits, and one at Vandenberg Air Force Base in California to handle southbound launches to polar orbit. Since polar orbits cover all of Earth's land area they're preferred for reconnaissance satellites, allowing them to snoop on adversaries, frenemies, and outright enemies wherever they might roam. What delighted the White House and concerned the Kremlin was that the Space Shuttle had the capability to retrieve spacecraft as well as deploy them. In theory, a Shuttle could launch from Vandenberg at just the right moment to snatch a Soviet spy satellite over Antarctica, then return to land in California after a single orbit. Presumably the American president would then claim to know nothing about why a Soviet spacecraft just disappeared without a trace.

Diplomatic absurdity aside, the Shuttle's large payload bay and high reentry maneuverability (required to enable single-orbit aborts after polar launches) made such missions technically feasible. Cold War logic being what it was, the Soviet military establishment eventually decided that if a NATO power was going to have such a capability, the USSR had to have it, too. The Soviet space design bureaus were then told to copy the Shuttle as best they could, and so Buran was born.

At the time it was built, and possibly to this day, the Space Shuttle was the most analyzed engineered system ever built by human hands. Its mission requirements called for a significant amount of aerodynamic maneuverability and good handling qualities across speeds ranging from about 200 miles an hour at landing to over 17,000 miles an hour at the start of reentry. To guarantee that the vehicle could perform as intended, thousands of hours of wind tunnel tests were conducted at subsonic, transonic, supersonic, and hypersonic speeds across a range of gas densities and temperatures to simulate the full-scale Shuttle's launch and entry environments. Knowing that the Americans had done this, and wanting to save money wherever possible amid the stagnating communist economies of the post-Brezhnev years, the Soviets elected to just duplicate the shape of the American Shuttle rather than repeat any of this work. Given the obvious brilliance of the Soviet human spaceflight heritage, this is a bit of a disappointment.

The most significant divergence between Buran and the Space Shuttle was its propulsion system. The American aerospace industry invested heavily in solid rocket motor technology during the Cold War to perfect its ballistic missiles, while the Soviets were mostly happy with the workings of liquid rocket engines. As a result, the American Space Shuttle leveraged big solid motor know-how by including two massive solid rocket boosters in the Space Shuttle's launch stack, while the Soviets used kerosene and oxygen-burning liquid boosters in their place. While liquid rocket engines tend to be more expensive than solids, this choice makes sense for a launch vehicle. Unlike ballistic missiles, launch vehicles don't need to be ready to fly at a moment's notice, so it's okay if it takes hours to fuel the vehicle before liftoff. Since liquids can launch more payload per pound of propellant and can be shut down benignly in the event of launch trouble (once lit, it's very difficult to stop solid rocket motor combustion), they're a more appropriate choice for a reusable launch vehicle. Since the hydrogen-powered main engines were mounted to the core propellant tank on the Buran stack, it had the flexibility to launch large payloads (like, say, space laser battlestations) as the semi-reusable launch vehicle Energia.

Soviet industry was strained to the breaking point by the catch-up defensive programs of the 1980s. By the end of the decade, the Communist Bloc was bankrupt and the west was declaring victory in the Cold War. Buran was one of the most expensive programs the USSR ever embarked upon, even with all the cost-cutting and corner-cutting measures in its development, and it surely played a significant role in the fall of the Soviet Union. In the end it only flew once, unmanned, before being mothballed and destroyed when the hangar housing Buran collapsed in 2002. But fly it did:

Aggie Bonfire

For almost a century, once a year students at Texas A&M University take it upon themselves to assemble a large stack of wood, douse it with jet fuel, and light it on fire. You can read more about that here:
Aggie Bonfire

Robert Gates, who at various points in his career served as Director of Central Intelligence, Secretary of Defense, and President of Texas A&M, once said of the university that "From the outside looking in, you can't understand it. From the inside looking out, you can't explain it." The former Agricultural and Mechanical College of Texas is an institution rich in tradition and ritual, and has a cult(ure) that must seem often baffling to outsiders. Among other things, upperclassmen can insist that those in newer classes do push-ups in exchange for saying certain privileged words, and are typically taken seriously while doing this (at least during football season). By comparison, the value of setting lots of stuff on fire is obvious.

For all of the 20th Century and the first decade of the 21st, A&M's  chief athletic nemesis was a certain university in Austin, and the tradition of Bonfire quickly became an annual rallying cry against the Longhorns. Few parts of the university's history better show the ferocious ambition of the Aggies than the almost Kurzweilian growth in the Bonfire stack's height in its first half-century. By 1969, while men from Earth walked upon the face of the Moon, the Bonfire reached a height of 109 feet, in what remains a record for bonfires anywhere. Surely history has shown the 1960s to be a decade ahead of its time. Cooler heads prevailed after that, and the university administration imposed clear limits on height and diameter out of concern for students' safety and the surrounding buildings' fire-suppression capabilities.

The administration's endorsement of Bonfire came to a painful, jarring halt in 1999 when the stack collapsed in the early-morning hours a week before its scheduled ignition. 12 students were killed and 27 injured when the joints holding the 5,000 logs together buckled and failed in what hopefully will remain the most traumatic single event in the university's history. An investigation revealed inadequate engineering of the structure, a lack of meaningful management accountability, and unsafe work practices to be contributing factors, and since then no Bonfire has burned on the A&M campus.

Four years after the tragedy of 1999 an independent Bonfire burned once again, this time far from campus proper, and under the supervision of professional structural engineering. A year after that a memorial was erected on the site of the collapse, and it's as much an introduction to that nebulous-but-meaningful Aggie Spirit that Gates was trying to talk about as it is a monument to the senselessness of what happened. The Aggies and Longhorns no longer play football each year, but Bonfire burns on, and the memories stay with us, and, hopefully, we learn from our mistakes.

The Scunthorpe Problem

It's interesting how complex engineered systems can seem to develop a personality without any conscious design intent. Sometimes automated obscenity filters develop an adorable combination of prudishness and boneheadedness, blocking perfectly normal (though sometimes awkward) proper nouns that contain letter strings that would be obscene on their own. You can read more about that here:
The Scunthorpe Problem

The phenomenon is named for the town of Scunthorpe in North Lincolnshire, England. In 1996 AOL blocked Scunthorpe residents (Scunthorpians?) from registering accounts due to a certain four-letter string toward the beginning of their town's name. Take a good long look at the word and see if you can find what I'm talking about.

Years later the same problem arose, and was eventually corrected, in Google's language filter. The problem is by no means limited to eastern England, of course, and individual users like Craig Cockburn (Wikipedia helpfully suggests this is pronounced "coburn") and Herman Libshitz (no such help this time, alas) ran into trouble registering accounts with various email services due to a lack of specificity in the obscenity filters' scrutiny.

The must puzzling case is that of Linda Callahan, who was unable to register an account with Yahoo! for some time due to the presence of "allah" in her family name. I'm not quite sure what the world is coming to when the Arabic word for the God of Abraham and Isaac is considered obscene. Oh, well, at least Ms. Callahan was eventually able to check her email in peace.

Natural Nuclear Reactor

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Nuclear fission reactors are not exactly a human invention. Under the right conditions naturally-occurring fissile ore can spontaneously begin a nuclear chain reaction. You can read more about that here:
Natural nuclear fission reactor

The Wikipedia article specifies that it refers to natural nuclear fission reactors, presumably to contrast the concept with the large number of natural nuclear fusion reactors (i.e. stars) in the universe. You could just as easily refer to the fission reactors as such and the stars as thermonuclear reactors (since fission can happen at any temperature while fusion requires obscenely hot places to work), so I left out the "fission" part out of this post's title. Whatever they're called, the basic idea is that whenever a sufficient amount of rich uranium ore gathers in a place with minerals that can moderate the speed of the reaction-sustaining neutrons without absorbing them completely, a self-sustaining nuclear reaction will begin. That's just how physics seems to work in this universe.

While stellar thermonuclear reactors abound in the cosmos, only one natural nuclear reactor is known to have existed on Earth. Nearly two billion years ago, in what's now west Africa, all the conditions were right for the Oklo reactor to begin reacting. This Scientific American article provides a good overview of the fascinating details of Oklo's discovery and history. It looks like the reactor complex operated in an on-off cycle for a few hundred thousand years, running while groundwater seeped into the sandstone encasing the uranium ore, until the temperature rose enough to boil the neutron-moderating water away. Eventually fission products poisonous to further reactions built up until the reactor shut down for good 1.7 billion years ago. Surely this wasn't the only place this happened, but only at Oklo did the scene remain undisturbed until uranium miners came along in the mid-20th Century.

The numbers at Oklo give some insight into the tremendous energy that heavy atoms pack. Since the reactor complex wasn't designed for power, geologists and nuclear physicists estimate that it averaged about 200 kilowatts during its life, or about 270 horsepower in the deeply awkward and inconsistent units of the Imperial system. That might not sound like much, but consider that during Oklo's active life it consumed about five tons of uranium, converting it into lighter fission products like neodymium and ruthenium. Five tons of nuclear fuel sustained a power equivalent to a reasonable sports car engine at full throttle for hundreds of thousands of years. Oil might be the backbone of our energy economy for now, but it ain't got nothin' on uranium.

Cosmic Ray Spallation

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Carl Sagan famously said that people are starstuff contemplating the stars. His point was that the atoms are not now as they've always been, and that stars are the furnaces that churn the light atoms that emerged from the Big Bang into the heavier stuff that composes the planets and the creatures of Earth. This is how it usually works, but it's not always so. As we've seen before, the whole universe once made heavier atoms like the inside of a star, and some of the matter of our planet is only made when blindingly fast particles from deep space slam into Earth's atmosphere and surface. You can read more about that here:
Cosmic ray spallation

There's a lull in the periodic table of the elements between helium and carbon. Helium was made in tremendous quantities during the Big Bang and by several generations of stars before the solar system came into being, and an efficient process exists in large stars to convert helium into carbon. Lithium, beryllium, and boron, the elements between helium and carbon in atomic weight, don't fit neatly into these standard creation stories, though, and are quickly burned up in stars and converted into more mundane stuff like carbon, oxygen, and neon.

As rare as these elements are, they still clearly exist on Earth. Without lithium batteries, cell phones would still be the size of bricks. Without beryllium, emeralds (beryllium ceramics with a hint of chromium) would be nowhere to be found. Without boron, the green flash of triethylborane igniters (pictured in a SpaceX Falcon 9 test above) would look much more mundane. The reason Earth is graced with their presence is because space is full of violent explosions that create particles that fly through the cosmos at close to the speed of light. When these small nuclei collide with each other, or with the atoms in planets and interstellar dust, they blast the atoms apart, and small fragments, the stuff of a boron atom, say, are left behind. It doesn't happen often enough to compete with the output of the stars, but it does happen often enough that emeralds aren't as rare as platinum, at least in the Earth's crust.

Not everything made by cosmic ray spallation is built to last. A small amount of radioactive carbon is constantly coming into being in the upper atmosphere when neutrons generated by cosmic ray collisions knock protons out of the nitrogen atoms that surround Earth. The neutrons take the protons' places, and the nitrogen is transmuted into carbon-14, which is chemically identical to the ordinary carbon-12 that makes everything from proteins to airplanes to diamonds, but radioactively decays with a half-life of about 5,700 years. To put that in perspective, the pyramids at Giza have about a millennium to go before they've been around for a carbon-14 half-life.

About one in a trillion carbon atoms on Earth is radioactive, and since the supply is constantly being replenished living things have the same amount of carbon-14 in their tissues as long as they keep breathing and eating. Once the mortal coil is shuffled off, though, the carbon decays without replacement, and by measuring the ratio of radioactive to ordinary carbon the time of death can be established with decent precision. Radiocarbon dating, as it's known, has become a staple of archaeology since the physics here was first figured out. Several other radioactive isotopes are also made by cosmic ray spallation, and provide a range of dating scales for similar work. As odd as it sounds, the afterglow of far off worlds gives us some of the best clues about how things work here at home.

The Jimmy Carter Rabbit Incident

On April 20, 1979, President Jimmy Carter was attacked by a large swimming rabbit in rural Georgia. You can read more about the incident here:
Jimmy Carter rabbit incident

Seriously, go read that first sentence again and ponder this for a moment. White House press secretary Jody Powell had this to say about the incident:

The President confessed to having had limited experience with enraged rabbits. He was unable to reach a definite conclusion about its state of mind. What was obvious, however, was that this large, wet animal, making strange hissing noises and gnashing its teeth, was intent upon climbing into the Presidential boat.

Apparently many on Carter's staff were incredulous at his story at first blush, unwilling to imagine that rabbits could swim, or perhaps just unwilling to imagine that a rabbit could appear menacing to the leader of the world's biggest economy and second-largest nuclear power. Randall Munroe helpfully puts the event into its proper historical context here:

Indeed. Let us never forget the killer swamp rabbit of Georgia.

Coelacanth

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One of the most remarkable discoveries in the field of biology in the 20th Century was the recognition that coelacanths, lobe-finned fish eerily similar to land vertebrates in many ways, still roam hundreds of feet below the surface of the Indian Ocean. For a century, the fish was believed to be extinct since the time of the dinosaurs. The Intelligent Life piece referenced in the image credit has more to say on the matter (including the helpful pronunciation tip: "see-la-kanth"), and as is our custom, the Wikipedia article is here:
Coelacanth

Among other things, the Intelligent Life piece contains such fun facts as the realization that lungfish have a genome 40 times longer than that of humans. This seems odd to me, but consider:

• The notion that humans are somehow "more evolved" than other animals simply because our brains are complex is somewhere between nonsensical and silly.
• Nature doesn't much care about what seems reasonable to us.
• I haven't taken a biology class since 2007.

In any case, a heated debate arose in the mid-19th Century over whether the lungfish or the coelacanth was a more direct ancestor of modern terrestrial vertebrate life. As it turns out, genetic evidence suggests that the lungfish is closer to that branch on the evolutionary tree, but the coelacanth is still "more closely related to us than it is to a salmon or a shark." Whatever the lineage, it's a fascinating creature to watch, and our oceans are surely richer for having the coelacanths around:

ZMC-2

The only metal-skinned airship ever flown was built at Grosse Ile, Michigan in 1929, and was operated by the US Navy until her scrapping in 1941. You can read more about the ship here:
ZMC-2

Aerospace aluminum alloys are immensely strong and not very dense, which makes them ideal for applications where strength without (much) weight is essential. Unfortunately many alloys, particularly early in the history of metal aerospace structures, suffer from corrosion problems over the service life of an aircraft. Pure elemental aluminum has fantastic corrosion resistance, not because it resists oxidation, but because a thin layer of aluminum oxide (or corundum if you're into fancy mineral names) quickly forms on any exposed aluminum surface, and this coating is chemically identical to the stuff that sapphires and rubies are made of. Rather than flaking away as rust, weakening the structure as iron oxide does to steel, a little corundum goes a long way to protecting aluminum from the elements. Given the strength of aluminum alloyed with elements like copper, magnesium, and silicon, and the corrosion-resistance of pure aluminum, metallurgists developed a method in the 1920s to place a thin aluminum layer atop alloy plate without leaving behind a weak bondline. The result was alclad, and ZMC-2 was the first full-scale demonstration of an aircraft built with this technique.

In addition to the innovation in the material that composed her, ZMC-2 broke new ground in her structure. The orthodox way to build a zeppelin was to place bags of lifting gas in a metal frame, then cover the frame with fabric. ZMC-2 did away with that complexity by making the aluminum skin airtight, sealing in 200,000 cubic feet of helium without need for a separate structural truss or helium vessels. As long as the structural material is light enough, this simplicity ought to decrease vehicle weight, although installing the 3.5 million fluid-tight rivets must have been a pain in the ass. Today a less laborous technique like friction-stir welding would probably be used instead.

The most fascinating part of ZMC-2's story for me is the drama that ensued when she became buoyant for the first time. Blimps and conventional zeppelins fill flexible bags that can be evacuated of air with lifting gas in order to make lift, which is a relatively straightforward process. Since ZMC-2's helium vessel was rigid, engineers needed a way to extract the nitrogen and oxygen within while replacing it with helium, all while the gases were vigorously mixing at room temperature. Since helium was and remains rare and expensive on Earth, minimizing the loss of lifting gas was critical. Replacing the ambient air within with (cheap) carbon dioxide, which mixes more slowly with helium, seemed an elegant solution at first, until, as Wikipedia puts it, "a bright young engineer" pointed out that the ship would be many tons heavier when filled with carbon dioxide, stressing the structure unacceptably. Once the necessary sections of ship were reinforced the helium purge proceeded without apparent incident, and modern engineers are left hoping we can be so clever and observant when the time arises.

The Kola Superdeep Borehole

The deepest point beneath the Earth's surface created by humans is an experimental borehole drilled by the Soviet Union between 1970 and 1989 in the Kola Peninsula in northwest Russia. You can read more about it here:
Kola Superdeep Borehole

The deepest spur of the borehole, labelled "SG-3" by the project's geophysicists, bottomed out after 19 years of on-and-off drilling at a depth of 12,262 meters (40,230 feet for those who don't like moving decimal places to convert units). This is short of the original depth goal of 15 kilometers, first due to mechanical problems with the drill and then from unexpectedly high temperatures in the well. In 1984 a 5-kilometer-long piece of drill string failed and was abandoned in the central hole. The project was forced to backtrack the length of the broken drill string and start drilling again off a side borehole, but when the temperature in SG-3 reached 180 degrees Celsius further progress was deemed unfeasible and the project fell into disarray amid the collapse of the Soviet Union and the painful depression that followed.

Propaganda value was part of the reason why the Soviets chose to dig so deep at Kola, since there was no equivalent western program that could claim to reach deeper into the Earth. That said, a good deal of geophysical knowledge came from the Kola borehole during its prime, including a better understanding of the transitions that happen in rock structure deep within the Earth's crust and the discovery of large amounts of water and hydrogen sequestered far below the surface. It's a shame an earlier American program to reach deep under the oceanic crust faltered due to a lack of funds.

Nowadays the deepest wells beneath the surface are drilled for profit rather than science. Before its horrifying and public demise the Deepwater Horizon platform drilled to within a mile of the depth of the Kola borehole to extract oil lurking beneath the Gulf of Mexico. Drilling technology has advanced so quickly that getting the oil out of the ground wasn't anywhere near as difficult as stopping it once it the flow was started. The era of herculean effort to sip petroleum won't last forever, though, and hopefully this technology will be applied to exploration in the open-ended sense once again. After all, something seems odd about a people who have touched the Moon but never reached very far under their own feet.

Operation Mincemeat

In the spring of 1943 the British Security Service MI5 launched a plan to place false intelligence documents in the hands of the Abwehr. The objective was to convince Hitler that Allied forces intended to invade Greece and Sardinia that summer, rather than their true objective of Sicily, and it succeeded spectacularly. Ben Macintyre wrote a wonderful account of the full operation, but more briefly you can learn about the plan and its execution here:
Operation Mincemeat

Sicily was the obvious target of choice in the western European theater once the campaign in north Africa was concluded and the invasion of Normandy was not yet ready. To improve their chances of success Allied intelligence attempted to divert as much Axis resistance as possible through a systematic campaign to convince the Axis heads of state that Sicily was not going to be the next target, even though strategically that conclusion seemed inevitable. To help, a British Intelligence team lead by Charles Cholmondeley, Ewen Montagu (brother of table tennis enthusiast and Soviet spy Ivor), and Ian Fleming (yes, that Ian Fleming) enlisted the help of the espionage demimonde of neutral Spain, the submarine HMS Seraph, and the body of a Welsh vagrant named Glyndwr Michael, disguised as a Royal Marine officer. Spy folks have come up with some odd ideas over the years, but this stands out even among that crowd.

Michael died, possibly by accident and possibly by suicide, in London in January of 1943 after ingesting a lethal amount of phosphorous-based rat poison. Having no next of kin, no property, and few if any acquaintances, it was easy for the reality of Glyndwr Michael to disappear. MI5 agents crafted an elaborate backstory for a Marine Major named Bill Martin and assigned it, along with a briefcase full of official-looking documents outlining a planned invasion of the islands of the Aegean and Sardinia, to Michael's body. The plan was for the newly-minted officer to be placed just off the coast of Spain, floating face-down in a life jacket, providing a reasonable simulacrum of a drowned plane crash casualty. Hopefully someone would find him shortly thereafter and take him ashore for examination by Spanish and Nazi spies.

Once the plan's form was finalized and the documents made ready, the fabricated Marine was shuttled to the coast of Andalusia by way of the Seraph in an airtight capsule filled with dry ice for preservation. In the early morning hours of April 30, after some brief drama on the surface that involved rigging the seemingly-unsinkable capsule with plastic explosive to facilitate destruction of its evidence, Major Martin was sent on his one-way mission of deception. Later that day he was indeed found by local fishermen, and eventually worked his way to the Spanish authorities.

Mincemeat, as the operation was code-named, was a production that only made sense if you wanted to believe it anyway. Phosphorous poisoning doesn't look much like drowning, and after spending three months in a morgue, Michael's body was in poor condition to pass for a recent plane crash victim. Still, the Germans were eager for any news about Allied plans after their anxious retreat from Africa, and were willing to look past the parts that didn't fit together and see a coherent story behind Major Martin. The record seems to show that Hitler found the plant convincing, and even after the invasion of Sicily began he was convinced that it was nothing more than a diversion from a real, upcoming assault further east in the Mediterranean. Sometimes the most convincing lies come from those who don't speak at all.

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Wilhelm Scream

No, not that Scream

The Wilhelm scream is a stock sound effect that's been used in over 200 films and television shows since its introduction in 1951. You can read more about it here:
Wilhelm scream

If you've seen any of the Star Wars or Indiana Jones movies or almost any Disney movie made in the '90s, you've heard the Wilhelm scream. It's not, strictly speaking, a good effect, but it's become something of an inside joke in Hollywood. Quentin Tarantino, the guru of film-making pastiche, seems to have a deep affection for the Wilhelm scream, using it in many of his movies as well. This is probably the surest sign of the campy impact the effect has had.

To get a better sense of what I'm talking about, you may find the following video helpful:

The Gunpowder Plot

On the fifth of November of 1605 a group of conspirators planned to destroy the British House of Lords, with the objective of assassinating King James and installing his daughter Elizabeth as a Catholic head of state of the United Kingdom. The plot failed when Guy Fawkes was found with 36 barrels of gunpowder after an an anonymous letter tipped off the authorities, and you can read more about it here:
The Gunpowder Plot

To be honest, I don't know a whole lot about 17th Century British history, but since Hugo Weaving's character in V for Vendetta insists we remember the Gunpowder Plot, there you go. Clearly the conspiracy was part of the dark political-religious hypnagogia that Europe was in the middle of the last millennium. The ideas of Thomas Jefferson and Karl Marx, a political man aloof to religion and one hostile toward it, have so thoroughly embedded themselves in the public consciousness of the world today that it's difficult imagining people in the western world seriously contemplating blowing up buildings to install religious dictatorships. The worst acts of terrorism in our time seem to be more motivated by a rejection of foreign influence, or of any authority at all, rather than by a pragmatic will to change the guard.

But back then the Bishop of Rome also governed a significant part of what's now Italy and the Thirty Years' War, a savage generation-long conflict between Protestant- and Catholic-aligned states that was the single worst thing to happen to Europe since the Black Death, was nearly at hand. Christianity, corruption, and government were deeply mingled, and the Church was hemorrhaging in the bloodiest way that could then be imagined. No wonder America seemed like such an appealing place.

To celebrate the successful thwarting of the attack, a tradition emerged of lighting bonfires and fireworks on that day in the UK. This is reasonable, because bonfires are cool.

Geminga

One of the closest and youngest neutron stars to Earth is a brilliant gamma-ray source 800 light-years away in the constellation Gemini. It turns out to be closely tied to the history and present makeup of the galaxy near the solar system and the recent history of life on Earth, and you can read more about it here:
Geminga

Known as Geminga, the star baffled astronomers for two decades until it was found to send out faint pulses of X-rays four times a second with astonishing faithfulness, an unambiguous signature of a pulsar.Until that discovery what was known was that there was a very strong beacon of gamma radiation coming from Gemini that didn't seem to be connected to any physical object. The name its discoverers' chose was a clever double entendre, both a prosaic abbreviation of "Gemini gamma-ray source" and a clever adoption of a Milanese dialect word meaning "It's not there."

Geminga is there, and is close as far as stellar remnants go. It's also young, cosmically speaking. Its main sequence life ended in a spectacular supernova about 300,000 years ago. People more or less as we are now roamed the Earth back then, in Africa, the Middle East, and Europe, and since Gemini is close to the celestial equator people in both hemispheres would've seen an explosion bright enough to cast shadows at night and see in broad daylight. While they gazed at the sky and puzzled at what was going on, the supernova was so powerful it blasted away much of the interstellar medium around the Sun, and to this day the space around us bears the scar from Geminga's final days of stellar life. Meanwhile high-energy cosmic rays rained down upon the Earth, subtly altering the DNA of the Africans and the Neanderthals. As the Local Bubble bears  the mark of Geminga, so do our genomes.

At least, that's how the story was told in my undergrad astronomy class. Apparently the consensus is now that a series of supernovae in the Pleiades is the more likely explanation for the dearth of matter near the Sun. Either way, we know more than we once did, and it's always stirring to know how we're connected to the cosmos around us.

Nuclear Engine for Rocket Vehicle Application

From the beginning of the space age to the end of the Apollo program in 1972, the United States (and to a lesser extent the Soviet Union) took a serious look at using nuclear reactors for spacecraft propulsion. In the US, the program was known as Nuclear Engine for Rocket Vehicle Application, or NERVA, and resulted in a design deemed flightworthy by NASA before the program's cancellation. You can read more about it here:
NERVA

Rockets work by adding energy to a propellant, then using a nozzle to harness this energy into momentum used to drive the ship forward. Thermal rockets start the process by heating the propellant up, chemical thermal rockets in a combustion chamber, and nuclear thermal rockets in a reactor. Less dryly, you can think of a nuclear thermal rocket as a very hot teakettle, powered by a nuclear reactor, with the spout replaced with a nozzle intended to shoot out steam as fast as possible. By "very hot," I mean hot enough to melt steel, and by "as fast as possible," I mean faster than satellites in low Earth orbit. Uranium and plutonium pack a big kick in a small package.

Why go to all the political and, potentially, environmental trouble of launching a nuclear reactor into space? The answer has to do with the materials used to build the nozzle, and the propellant exhausted through it. The hotter the propellant is, the faster its molecules are going on average, and therefore the more thrust it delivers per gram of exhaust. This is why hotter-burning engines are more efficient, but there's a maximum temperature any practical nozzle can reach before it weakens, melts, or does something else bad from an engineering standpoint. For the same temperature, molecules with lower molecular weight move faster, so ideally you'd use the smallest molecules available. For practical engines, that turns out to be molecular hydrogen.

Chemical rockets burn fuel and oxidizer, releasing energy and creating propellant in the form of the reaction's product in the same step. This means that a chemical rocket designer doesn't have direct control over the exhaust composition. Adding unburned hydrogen to the exhaust (a trick used on the Space Shuttle Main Engines) only buys a little bit of performance until the exhaust temperature decrease nullifies any efficiency increase from reduced molecular weight. Since nuclear thermal rockets keep the fuel (the reactor's uranium) and propellant separate, virtually any propellant can be used. For this reason, nuclear thermal rockets typically were designed with hydrogen in mind, but ammonia has also been considered due to its relatively low molecular weight and excellent heat transfer properties.

Most spacecraft propulsion strategies offer high thrust but low efficiency (like chemical rockets) or high efficiency at low thrust (like ion engines). NERVA's thrust couldn't quite match that of chemical rockets like the SSME, and its thrust per unit propellant (specific impulse, a good measure of mission efficiency for spacecraft engines) wasn't as good as an ion thruster, but it packed a combination of both that was nearly perfect for sending large payloads from Earth to Mars in a short amount of time. Since the most sensible program for such an engine was human exploration of Mars, extensive NASA study began on this subject in the late-1960s and early-1970s, with a goal of boots on the red planet by 1980 if the funding held up. In the event, the funding was axed, and NASA barely survived the development of the Space Shuttle, a programmatic consolation prize for the loss of people on Mars in the 20th Century.

Still, the physics of nuclear reactions and hydrogen through the nozzle haven't changed since 1972. NERVA, or an engine much like it, will almost certainly be involved when people finally do start crossing deep space to venture to the planets. Ideas that make sense sometimes get shelved for a while, but one day NERVA's true time will come.

History of Geometry

Humans evolved as pursuit predators, so it makes sense that understanding the relationships between form, space, and physical objects is an essential part of the way our brains work. Geometry is such an intuitive human faculty, many people never give it a second thought, but the history of knowledge is full of profound insight lurking when the most intuitive assumptions are contemplated. The history of geometry is no different, and you can read more about what I mean here:
History of geometry

Literally, geometry means "Earth measurement" in Greek, but since Earth is complicated, geometry typically starts with more primitive thing like points, lines, and arcs. It's difficult to define exactly what a point, a line, or an arc are, but we seem to have a reasonable grasp of these things even though they're difficult to define by themselves. As one of my math-major friends put it:

"What is a point? Geometricians can't say, but the axioms describe how they behave, and how they interact with lines, also undefined. You might as well call them tables and chairs, or pips and peeps."

Since the time of Euclid geometry has been built on the process of deriving theorems from each other and from fundamental axioms. Theorems are the children of axioms and the rules of logic, so they're transparent and well-insulated from mystery, but the rules and axioms themselves are a bit mysterious. They don't really come from anywhere but assumptions about reality. To clarify, let's talk about parallel lines for a moment.

What does it mean for two lines to be parallel? Intuitively you might guess that two lines are parallel if they point the same direction, that if this is the case the lines never meet (or, more rigorously, meet at infinity), and that there ought to be a way to prove this from some more basic information about the construction of reality. Euclid and a small army of mathematicians who came after him for two millennia tried to do that and failed every time, having to accept that "parallel lines meet at infinity" is an axiom.

Since axioms aren't proved from anything, it's reasonable to ask what happens if you change them. What if parallel lines meet at a finite distance, or diverge forever at infinity? That seems nonsensical if you think of space as an infinite homogeneous grid, like a sheet of graph paper in every direction, but what if space curves and puckers like a hammock on a lazy afternoon?

In the 1800s geometers began seriously looking at what would happen in such a world. Surprisingly, such a world is counterintuitive but conceivable, and geometry where parallel lines bend toward or away from each other seemed to be fertile to new, consistent theorems. It was interesting, but many thought there was a touch of esotericness to these theories. Charles Lutwidge Dodgson went so far as to write a scathing critique of what he saw as a debasement of mathematical rigor among those working on non-Euclidian geometry. All this critiquing came to a screeching halt when the theories of Albert Einstein and the experimental confirmation that shortly followed showed unambiguously that we live in a world where straight lines ain't necessarily straight.

The history of geometry is a rich subject, and there's much more to it than knowledge of parallel lines. There's more than I could possibly hope to cover as a layman in one blog post, so here's one last story, as told by someone indispensible in any discussion of math, Vi Hart. Pythagoras, one of the giants of pre-Socratic philosophy and founders of geometry, may totally have murdered a dude over the square root of 2:

You might say that's an... irrational thing to do.

The Portland Head Light

The oldest lighthouse on the coast of Maine is located at Cape Elizabeth, just south of Portland. It was commissioned by president-elect George Washington in 1787, finished four years later, and you can read more about it here:
Portland Head Light

From the perspective of aesthetics the coast of Maine is beautiful, but from the perspective of navigation it's a nightmare out of the fiction of Lovecraft. Much of the coast was encased in kilometers of ice until just a few millennia ago, and when the glaciers retreated they carved deep jagged gashes into the bedrock from New Hampshire to New Brunswick. As the oceans warmed and expanded, the valleys turned to fjords and the hills into a vast field of islands and reefs. There simply hasn't been time for erosion to temper the sharp will of the land, so the lighthouses of Maine are an essential part of keeping ship traffic bound for Portland, Bath, and Bar Harbor afloat.

Lighthouses are charming in part because they're so practical. The need to not run your ship aground on a sharp piece of granite dictates function essentially the same way whether you pilot a clipper, a trawler, or the Queen Mary 2. There's thus little need to ever update a lighthouse's exterior, so even as the whale oil lamps are replaced with arc lamps, the house itself timelessly blinks on.