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I'll split this into two sections.Flight InstrumentsNearly every modern aircraft has six critical flight instruments, all arranged in what is called the sacred six-pack (or some variation thereof). With these six flight instruments a pilot can fly the aircraft both VFR (visually) and IFR (without being able to see outside).At the top left is the airspeed indicator. It measures indicated airspeed (which is an approximation of true airspeed). In the above image, the aircraft is moving at 74 knots (85 MPH). The white band indicates the safe range for flap extension, the green band the normal operating speed range, and the yellow band the smooth-air-only range. The white line at 40 knots is the stall speed with full flaps; the red line at 160 knots is the never-exceed speed.Top middle is the attitude indicator. It displays the aircraft's pitch and bank using a pictorial representation of the horizon line. The orange chevron in the center is used to reference pitch (with major and minor ticks in 5- and 10-degree increments), and the orange arrow at the top is used to reference bank (with 10-, 20-, 30-, 45-, and 90-degree ticks). In the above image, the aircraft is level (not banking) with about a 5-degree pitch up.At top right is the altimeter, which measures altitude above sea level (or any standard datum plane). The small hand indicates thousands of feet and the large hand hundreds of feet. The above image shows the plane at 1,580 feet of altitude. The small window on the right and left side indicates sea level air pressure at the current location (left in millibars, right in inHg); the pilot sets this to the reported pressure to ensure accurate altimeter readings.Bottom left is the turn coordinator, two instruments in one. The airplane icon indicates rate of turn in degrees per second; the tick mark indicates a two-minute turn (3 degrees per second), which is a standard rate turn. The floating ball is the inclinometer, which indicates sideslip. Lateral forces move the ball to the right or left out of its "cage"; pilots reference this indicator to ensure their turns are coordinated, with no sideslip.At bottom center is the heading indicator. This gyroscopic compass indicates the aircraft's heading in degrees. In the above picture, the aircraft is heading 53 degrees. As it is gyroscopic, this compass does not naturally seek north and must be set against the aircraft's magnetic compass in order to have a meaningful reading.Finally, the bottom-right instrument is the vertical speed indicator. It indicates rate of climb or descent in hundreds of feet per minute. The above image shows the aircraft in a fairly steep climb of 950 feet per minute.VFR chartsThe FAA publishes charts for visual navigation, called sectionals, that every pilot learns to read. These charts are densely packed, especially in areas around major airports, and there's a lot of different symbols. The full legend can be found at http://flighttraining.aopa.org/pdfs/VFR_Chart_Symbols.pdf but for the sake of an introduction, I'll reproduce a portion of a sectional chart and describe some of the major features:This sectional shows Albuquerque, NM and surrounding area. The base map is a topographic map with lines of equal elevation (barely visible on the mountain range) and coloration based on elevation. Major visual features useful to navigation such as highways (including Highway 40), railroads, pipelines, power lines, and bridges are plotted and sometimes labeled. Natural features such as rivers and dry lake beds are plotted and labeled (such as Rio San Jose on the west side).Lines of latitude and longitude are drawn as thin black straight lines. Sectional maps always use a Lambert conformal conic projection so that lines of latitude and longitude are always parallel, which makes flight planning using a straightedge easier. The center line of latitude is labeled as 35 degrees.Built-up urban areas are displayed in yellow, with the names of cities in black light print. Smaller towns and settlements are depicted using hollow circles and lowercase labels.Albuquerque Int'l Sunport, being an airport with a control tower, is depicted in blue with its three runways. To the northwest, Double Eagle airport is also towered. The small star above both airports indicates the presence of nighttime lighting. Near the southwest corner of the chart is Alexander Airport, depicted in purple because it is uncontrolled (no control tower). In the center and just slightly south is Manzano-Mountain Airport, which is depicted as a circled "R" -- this indicates that it is private and landing is restricted to authorized aircraft only (usually the owner and his friends). On bottom of the map midway to the right side is another airport called Mountair; it is labeled with a hollow circle, indicating that its runways are short.Each airport has a "data block" nearby with the name of the airport on the first line, important frequencies (such as control tower ["CT"] or automated weather ["AWOS"]) on the next lines, and runway information on the last line. ABQ's last line ("5535 L 138 122.95") indicates that the airport altitude is 5,535 feet, it has runway lighting, the longest runway is 13,800 feet long, and UNICOM is available on 122.95 MHz (this is a frequency for communicating with ground services).Surrounding the airports are thick or fuzzy circles that indicate the extent of controlled airspace. The thick purple circles around ABQ indicate the edge of class-C controlled airspace at different altitudes. The altitudes are written in bold purple letters within the circles. The inner circle indicates class-C from surface to 9,400 feet, and the outer circle has two segments, the largest from 6,900 to 9,400 feet, and a smaller eastern segment that extens from 7,800 to 9,400 feet (due to the mountains to the east). The thin hatched blue line around Double Eagle indicates the edge of its class-D airspace, and the "75" in the hatched square indicates that class-D airspace goes from the surface to 7,500 feet, where it underlies the outer ring of ABQ's class-C airspace. The fuzzy puple lines around Alexander Airport and both of the Albuquerque airports indicates where class-E airspace goes down to 700 feet (in all other locations on this map, it goes down to 1,200 feet).On the western edge of the outermost portion of ABQ's class-C airspace is a hexagon labeled "ALBUQUERQUE"; this is a VOR, a radionavigation beacon pilots use to navigate without visual reference (in IFR flying). It's surrounded by a large compass rose oriented to magnetic north. Its data block indicates its name, its three-letter identifier (also in Morse code), and its frequency (113.2 MHz) and TACAN channel for military pilots (79X). The circled "H" at the upper right of its data block indicates that hazardous weather advisory information can be heard by listening to its radio transmission. The four frequencies listed along the top of the data block are four different Flight Service frequencies pilots can use for flight plan filing. The "ALBUQUERQUE" below the bottom of the data block indicates the call sign of Flight Service in this vicinity; in this case, "Albuquerque Radio".Light blue lines travel outward from the VOR's compass rose like spokes; these are victor airways, which IFR pilots fly along. Each one is labeled with its direction and its name (such as V611 which heads out southward). These airways connect together the different VORs: You can see V12 connecting ABQ VOR with another VOR on the eastern side of the map. To the right of V611 is a boxed figure "42" indicating the length of that victor airway is 42 nautical miles.Near the center of the map, two victor airways connect at a point labeled CYOTE. These are intersections, navigable points defined by the intersection of two airways. They each have five-letter names. These are also used by IFR pilots to fly from place to place.Obstacles on the map that pose a potential threat to aircraft are depicted as thick blue chevrons with dots at the base. A large obstacle is depicted southwest of Double Eagle. The "6277" in bold italic indicates the height of the top at 6,277 feet above sea level. Below it, the "400" in parentheses indicates that the obstacle is 400 feet high.Small black squares are used to indicate prominent man-made structures that are recognizable from the air, for purposes of navigation. On the very west side of the map are two such squares, labeled "bldgs" for buildings. On the east side midway towards the top is one labeled "stockyard."Each quadrangle (a rectangle formed by lines of latitude and longitude) has a maximum elevation figure, written in large blue text. The quadrangles in this map have MEFs of 8,300 feet, 11,000 feet, 7,100 feet, and 10,400 feet. These elevations are the lowest an aircraft can fly and still be 1,000 feet higher than any terrain in the quadrangle.Just to the east of the eastern edge of the ABQ class-charlie airspace is a purple flag labeled "CEMENT PLANT"; this indicates a VFR reporting point. These points are used by local control tower personnel to vector VFR aircraft (as in, "fly to the cement plan, then direct to the airport").At the bottom, midway to the left side, is a small parachute that indicates parachute jumping activity in that area.At the southeast corner of the map is a gray line labeled "VR100"; this is a military training route (MTR) that military aircraft fly.At the northeast corner of the map is an isolated mountain; a small circle indicates its peak is 8,897 feet. A crossed-hammers symbol indicates the presence of a quarry on its northeast side.At the top-center of the map are the Sandia Mountains, surrounded by a thin blue line with dots along the inside. This indicates a protected wildlife area, where airplanes are recommended against flying too low.Finally, on the eastern side of the map is Moriarty Airport; next to it is a glider icon with a "G" in a diamond indicating glider activity at that airport. A similar icon in the southeast corner has a "UA" in a diamond indicating unmanned aircraft (drone) activity.

One thing that can cause loss of inflection, is a millennia-long history of trade and conquest. This is true in the three instances I know of: English, Chinese, and Lebanese Arabic. Essentially, when a nation deals continuously with an influx of immigrants, conquerors, colonials, traders, and slaves who speak the host language poorly, the host-country’s native speakers tend to become very tolerant about dropped inflections.That said, this process of dropping inflections seems to work much better when the host language’s inflection system uses suffixes, instead of infixes. This was the case for English & Chinese.By contrast, I don’t see how this imperial simplification could succeed with a polysynthetic language like Georgian. When you look at a conjugated Georgian verb-form, like mivighe ts'erili, 'I received the letter', the verb’s root meaning is carried by the single consonant -gh-; most of the conjugated verb-form is inflection. Such abbreviated roots are absolutely the norm for verbs in Georgian (and in many other polysynthetic languages).An impatient or inept speaker might try to drop the end of such a verb form, but in Georgian that would strip off the verb’s core meaning, leaving only the person-agreement stuff and a preposition-like prefix mi-; the truncated verb would be reduced to gibberish.For a more familiar analogy, suppose I were to abbreviate the French verb nous partirons ‘we’ll leave’, as *nous irons, or perhaps as *nous tirons. Discarding the verbal root doesn’t work at all. But, if we omit just the verb-ending, the broken French *nous partir can still be deciphered, as “we leave.”In the case of Lebanese Arabic, some of the usual vowel-shift inflections got frozen as fixed words. Why did this simplification happen in the Levant, but not amongst other Arabic speakers? My guess is that several factors contributed:If you look at the ethnic makeup of the various Islamic empires, there were three main language families present in the mix:AfroAsiatic, including Arabic, Aramaic, Berber;Indo-European: SW Slavic, Greek, Armenian, Persian, Pashto;Turkic: Turkish, Turkmen, Kazakh, Uzbek, etc.Notably, Indo-European & Turkic languages inflect nouns and verbs with suffixes, so in the Middle-Eastern center of the empire, subjects and slaves from these language groups would tend to speak Arabic by ignoring the Semitic vowel-mediated inflections.In most of the Arab world, the prestige of Q’uranic Arabic has tended to limit drift in the vernacular language. But, Lebanon & Syria have large Christian populations, so those speakers have some immunity to the Q’uran’s linguistic conservatism.Lebanon & Syria have been a preëmininent commercial and imperial crossroads since pre-history, long before Islam arrived, so the local dialect’s grammatical simplification probably predates Islam’s unifying influence, anyway.Imperially-driven simplification isn’t my idea; I believe I read a brief reference to it, in one of John McWhorter’s books. BTW, I recommend McWhorter’s books, as accessible popularized accounts of interesting topics in linguistics.

This answer may contain sensitive images. Click on an image to unblur it.The name “Black Death” usually applies to a particular outbreak of the bubonic plague that seems to have begun in around 1338 in Central Asia. The outbreak arrived in Europe in 1346. The main outbreak in Europe lasted until 1353. Altogether, the Black Death is estimated to have killed somewhere between seventy-five million and two hundred million people across the Eurasian continent, making it one of the deadliest pandemics in all of human history.Unfortunately, it has become fashionable for people to write articles making fun of how stupid and ignorant people who lived during the time of the Black Death supposedly were. There are people online making fun of how people supposedly did all sorts of dumb things that actually made the plague even worse and resulted in more people dying—because apparently that’s something that people these days find amusing.In reality, many of the things that modern people claim medieval people did that supposedly just made the plague even worse are either things that never really happened at all or things that have been taken out of context and misrepresented to make medieval people look as stupid as possible.An example of someone making fun of how “stupid” people were during “the Dark Ages”Here is an answer I saw just a couple days ago on Quora in which someone relentlessly makes fun of how everyone in the “Dark Ages” was supposedly so “stupid.” He claims that they supposedly did things to get rid of the Black Death that are “so insane and absurd you’d rather start believing in the Flat-Earth theory,” a statement which seems to imply that he thinks that people during the fourteenth century thought the Earth was flat. (In reality, as I explain in this article from February 2019, it was common knowledge in western Europe in the fourteenth century that the Earth is a sphere.)The author never cites any sources, nor does he give any details about who did these things or where and when they did them and, in most cases, he doesn’t even explain why they did them; he simply asserts “people did this” and then proceeds to make fun of them for doing them, repeatedly asserting that the things he claims people did are all “obviously” stupid and that people clearly should have known better.As of the time I am writing this, that answer currently has 7,907 upvotes.Killing catsOne of the most popular stories about the Black Death on the internet (one which is—mercifully—not mentioned in the answer I reference above) is that people supposedly blamed the disease on cats, because they thought cats were creatures of the Devil, so they slaughtered cats en masse.Supposedly, by doing this, they inadvertently caused the disease to spread even further, since the plague was really being spread by fleas biting infected rats and then biting humans and because people supposedly killed off most of the cats in Europe, this supposedly caused the rat population to grow exponentially.The problem is that, first of all, there is almost no evidence whatsoever to support the idea that people in western Europe blamed the Black Death on cats. I wrote an entire article in November 2019 debunking this idea in depth, which I highly recommend people should read, but I will summarize the conclusions of that article here.Basically, the idea that people in the Middle Ages hated cats comes primarily from a total misreading of one decretal letter issued by Pope Gregory IX (in office 1227 – 1241) in either 1232 or 1233 titled Vox in Rama. This letter, which was written about a hundred years before the Black Death began, describes in great detail the bizarre heretical rites that peasants in the town of Stedinger were allegedly engaging in.The letter says absolutely nothing about cats in general being malevolent, nor does it say anything at all about cats causing diseases, nor does it contain any kind of injunction for people to kill cats. The letter does claim that, after the members of the Luciferian sect in Stedinger ate a ritual meal, a statue of a black cat would magically come to life, turn around, and raise its tail so that the members of the cult could kiss its anus. This has, for some reason, led many interpreters to believe that people in the Middle Ages thought all cats were creatures of the Devil and that they went around killing them.ABOVE: Illustration of Pope Gregory IX, author of the Vox in Rama, from a manuscript from c. 1482 containing a collection of his decretal lettersThe same letter, however, also claims that members of the sect would kiss the anus and mouth of a giant frog; that they would kiss an extraordinarily pale, emaciated man on the lips, causing them to immediately forget the catholic faith; and that members of the sect would worship a man with shaggy legs and a magical glowing penis. For some reason, modern interpreters have ignored all these other bizarre entities that the members of the sect are claimed to have venerated and focused exclusively on the cat.There are also a few surviving medieval depictions of people hunting and killing felines that some people have tried to cite as evidence for a massive pogrom against cats. In the vast majority of these depictions, though, it is abundantly clear that the felines being hunted and killed are wildcats, not domestic housecats.Furthermore, the existence of medieval depictions of people killing cats would not prove that there was any kind of massive anti-cat pogrom associated with the Black Death; it would, at the very best, only prove that some people in medieval Europe sometimes killed cats.Some proponents of the view that people in the Middle Ages hated and killed cats have also pointed to modern folk traditions about killing cats. In the vast majority of cases, though, these folk traditions cannot be reliably traced back to the Middle Ages at all.ABOVE: Illustration from a manuscript produced in Brittany, dating to c. 1430 – c. 1440, depicting hunters with dogs shooting arrows at a wildcat in a treeFurthermore, even if there really was evidence for a massive pogrom against cats during the Black Death (which there is virtually no evidence whatsoever to suggest that there was), there is no good reason to think this would have resulted in the plague being spread any more widely.For one thing, cats are far from the only animals in western Europe that hunt rodents. Dogs, weasels, snakes, and birds of prey do the job as well. In fact, as I discuss in this article I originally wrote in January 2017, the ancient Greeks more often saw weasels as the preeminent hunters of rodents than cats.For another thing, the idea that cats hunting rats would keep the plague from spreading is deeply flawed for several reasons. Cats only rarely hunt rats, since they generally prefer to hunt easier prey, such as mice and small birds, instead. Furthermore, cats that do kill and eat rats infected with the bubonic plague generally become infected with the plague themselves. Then fleas bite those cats and spread the plague to humans.Finally, cats are extraordinarily hard to track down and kill, meaning it would be virtually impossible for anyone to kill enough cats in a region to have any kind of substantial impact on the spread of the bubonic plague in that region.There is a great deal of evidence that people in western Europe during the Middle Ages actually liked cats and often kept them as pets. Cats were seen as useful animals because they were thought to keep away pests. The English poet Geoffrey Chaucer (lived c. 1343 – 1400) praises cats for their mousing abilities in “The Manciple’s Tale.” Cats also appear all over the place in medieval manuscript illustrations and they are usually portrayed in an endearing manner, often catching mice or being playful.Monks and nuns in particular were known for keeping cats as pets. The Ancrene Wisse, an early thirteenth-century monastic guide for anchoresses, advises that they should not keep any pets except for a cat. A folio page from a Dutch illustrated Book of Hours dated to the early fourteenth century contains an illustration of a nun holding a distaff while her pet, a white cat, plays with her spool.ABOVE: Illustration from an early fourteenth-century Book of Hours from the Netherlands depicting a nun with her pet catKilling witchesAnother popular claim on the internet is that the Black Death was widely believed to have been caused by witches, resulting in widespread witch burnings all across western Europe. This idea seems to partly be the result of a conflation of the Black Death with later outbreaks of the bubonic plague.There have been many outbreaks of the bubonic plague throughout history. The earliest known major outbreak of the bubonic plague was the so-called “Plague of Justinian,” which began in around 541 AD and devastated the population of the Roman Empire. The most recent major outbreak of the bubonic plague took place in China and India in the late nineteenth century.The term “Black Death,” however, generally refers to the specific bubonic plague pandemic that took place in the middle of the fourteenth century. At the time when this particular outbreak occurred, witch hunts had not yet become widespread. As I discuss in this article debunking misconceptions about the witch trials that I published in October 2018, witch trials did not become widespread in western Europe until long after the end of the Middle Ages.In fact, for nearly the entirety of the Middle Ages, the position of the Catholic Church was that witchcraft did not exist and anyone who claimed that witches existed was a heretic. Many ordinary people during the Middle Ages did believe in witches, but this belief was scorned by the church and witch trials were extremely rare. It was only in the Late Middle Ages (lasted c. 1250 – c. 1450) that the church even started to accept the existence of witches and it was only in the sixteenth century that witch trials started to become common.The height of the witchcraft hysteria in western Europe actually took place in the sixteenth and seventeenth centuries, which incidentally happens to be the same era that we usually call the “Scientific Revolution.” The era of the witch trials was also the era of William Shakespeare (lived 1564 – 1616), Francis Bacon (lived 1561 – 1626), Galileo Galilei (lived 1564 – 1642), René Descartes (lived 1596 – 1650), Baruch Spinoza (lived 1632 – 1677), Gottfried Wilhelm von Leibniz (lived 1646 – 1716), and Sir Isaac Newton (lived 1642 – 1727). There were outbreaks of the bubonic plague during the sixteenth and seventeenth centuries, but we usually don’t refer to those outbreaks as “the Black Death.”It is also worth noting that not all people accused of witchcraft were burned at the stake; in most Catholic countries, the usual method of execution for people accused of witchcraft was to be burned at the stake, but, in Britain, the usual method of execution was hanging. All nineteen of the people who were formally executed for the crime of witchcraft during the Salem witch trials (lasted February 1692 – May 1693) were hanged. (One man—Giles Corey—was pressed to death because he refused to plead guilty or not guilty. At least five other people died in jail.)ABOVE: Portrait of René Descartes (lived 1596 – 1650), who lived during the height of the witchcraft hysteriaKilling JewsThe claim that the Black Death resulted in people trying to annihilate domestic housecats is completely unsupported by evidence. Likewise, the claim that the Black Death resulted in widespread witch burnings is only arguably true if you include later outbreaks of the plague under the label “Black Death.” There is one group, though, that we know people definitely did lash out against during the bubonic plague pandemic in the middle of the fourteenth century: Jewish people.There was already widespread hatred for Jewish people among Christians in western Europe before the outbreak of the plague. In many places, Jews were forced to live in isolated ghettos. For some reason or another, during the Black Death, many Christians came to believe that the Jews were causing the plague by poisoning wells.Some modern scholars have speculated that this belief may have been fueled by the fact that, in many places, the Jews were living apart from everyone else and they also had to follow Jewish laws pertaining to sanitation, meaning some Jewish communities may have been less affected by the disease than the nearby Christian communities.In any case, the belief that the Jews were causing the disease certainly resulted in widespread pogroms against the Jews. Although these pogroms took place in many cities, the most infamous is the one that took place in the city of Strasbourg in eastern France on 14 February 1349 in which hundreds of Jews were burned alive over the course of a single day. Those who managed to escape the pogrom were forced to flee. It is unclear exactly how many Jews were killed during the Strasbourg pogrom of 1349, but 900 isn’t an implausible estimate.ABOVE: Manuscript illustration by Pierart dou Tielt dating to c. 1353 depicting a massacre of Jews during the time of the Black DeathIt is important to note, however, that many people did not believe that the Jews were causing the plague and there were actually government and church authorities who tried to protect them. Pope Clement VI issued a papal bull in July 1348 and a second one in September 1348 in which he urged all clergy to preach that anyone who claimed that Jews were causing the plague had been seduced by Satan. He further ordered them to do everything in their power to protect the Jews and to excommunicate anyone who harmed any Jewish person.Clement VI’s first papal bull Sicut Judeis from July 1348 declares, in this translation:“It cannot be true that the Jews, by such a heinous crime, are the cause or occasion of the plague, because through many parts of the world the same plague, by the hidden judgment of God, has afflicted and afflicts the Jews themselves and many other races who have never lived alongside them.”“We order you by apostolic writing that each of you upon whom this charge has been laid, should straightly command those subject to you, both clerical and lay . . . not to dare (on their own authority or out of hot-headedness) to capture, strike, wound or kill any Jews or expel them from their service on these grounds; and you should demand obedience under pain of excommunication.”Meanwhile, King Casimir III of Poland diligently protected the Jews of his own kingdom and enthusiastically opened up his borders to Jews fleeing persecution in other lands.ABOVE: Fresco by Mario Giovanetti of Pope Clement VI, who issued two papal bulls ordering all clergy to protect the Jews of Europe from pogroms and to excommunicate anyone who laid violent hands on any Jewish personFlagellating themselvesIt is also true that, during the Black Death in the mid-fourteenth century, some people did try to protect themselves from the plague by flagellating themselves in public, but there are some crucial bits of context that need to be given in order for people to really understand what happened.First of all, it is important to understand why some people thought it was a good idea to go out and flagellate themselves. They weren’t just doing it because they were weird masochists; they were doing it because they believed that the plague had been sent as a punishment from God for people’s sins and they believed that, in order to protect themselves, they needed to show God that they had truly repented of all their sins.These people came to believe that the only way to do this was by making a very public display of punishing themselves. They thought that, if they did this, God would see that they had repented and He would spare them from the plague. The flagellant movement isn’t evidence that people during the time of the Black Death were insane or stupid; it is evidence that they were desperate and afraid.It is also important to emphasize that this was a relatively short-lived fringe movement; it certainly wasn’t something that everyone was doing. In fact, Pope Clement VI—the same pope who ordered the clergy to protect the Jews—issued a papal bull in October 1349 in which he condemned self-flagellation as dangerous and heretical and ordered clergy to suppress the flagellant movement. The movement seems to have lost most of whatever popularity it ever had shortly thereafter.Self-flagellation certainly did not protect people from the plague and the pope knew this; Clement VI wouldn’t have condemned the movement if he had thought that the men marching through the streets in white robes continually lashing themselves with whips were actually doing something to prevent the plague.ABOVE: Manuscript illustration by Pierart dou Tielt dating to c. 1353 depicting a procession of people flagellating themselves during the time of the Black DeathWhat educated people really thought was causing the Black DeathIf we really want to know about the intellectual capacity of people during the time of Black Death, we should look at what the most educated people in the society believed was causing the illness. It so happens that we know what the most educated people in society believed was causing the Black Death; they didn’t think the plague was caused by cats, witches, Jews, or even necessarily direct divine punishment.Instead, the main hypothesis among the educated at the time was that the Black Death was caused by “miasmata” (i.e. infectious vapors in the air) that had been drawn up from the Earth by a triple conjunction of the planets Jupiter, Saturn, and Mars that occurred on 20 March 1345. A report written in October 1348 by the medical faculty of the city of Paris concludes, as translated by Rosemary Horrox:“We say that the distant and first cause of this pestilence was and is the configuration of the heavens. In 1345, at one hour after noon on 20 March, there was a major conjunction of three planets in Aquarius. This conjunction, along with other earlier conjunctions and eclipses, by causing a deadly corruption of the air around us, signifies mortality and famine, and also other things about which we will not speak here because they are not relevant.”“Aristotle testifies that this is the case in his book Concerning the causes of the properties of the elements, in which he says that mortality of races and the depopulation of kingdoms occur at the conjunction of Saturn and Jupiter, for great events then arise, their nature depending on the trigon in which the conjunction occurs.”“And this is found in ancient philosophers, and Albertus Magnus in his book, Concerning the causes of the properties of the elements (treatise 2, chapter 1) says that the conjunction of Mars and Jupiter causes a great pestilence in the air, especially when they come together in a hot, wet sign, as was the case in 1345. For Jupiter, being wet and hot, draws up evil vapours from the earth and Mars, because it is immoderately hot and dry, then ignites the vapours, and as a result there were lightning, sparks, noxious vapours and fires throughout the air.”Today we know that this idea was wrong, but it was far from stupid. In fact, everything about this hypothesis is rooted in some kind of empirical observation.As I explain in this article I wrote in April 2020, today we know that astrology is incorrect, but it really isn’t surprising that so many people in pre-modern times believed in it. People in ancient and medieval times did not know about all the natural forces that we know about today, but, when they looked up at the sky at night, they saw that it was full of stars.People also made a number of empirical observations that seemed to support the validity of astrology. For instance, they noticed that the stars changed over the course of the year and, as the stars changed, so did the seasons. They also noticed that the tides were correlated with the phases of the moon. Thus, it made sense to them to think those celestial bodies that they could see in the sky every night were having some kind of affect on the world around them. Astrology isn’t a stupid idea, but rather an outdated idea that has since been proven incorrect.Likewise, people noticed that people who were around other people who were infected with the plague tended to be more likely to get infected and that the disease seemed to spread more easily in smelly and unsanitary conditions, so they concluded that there was something in the air that was infecting people.There is even a grain of truth to this idea; while the bubonic plague is spread by infected fleas, the plague can actually take several different forms, one of which—the pneumonic plague—can be transmitted through the inhalation of airborne droplets containing the Yersinia pestis bacterium. In other words, in some cases, there may really have been something in the air that was infecting people.The report quoted above wasn’t written by stupid people; it was written by highly intelligent people working with the best information available to them. Those people just happened to be wrong.ABOVE: Photograph from Wikimedia Commons of the LH 95 star-forming region of the Large Magellanic Cloud, a satellite galaxy of the Milky Way, taken by the Hubble Space TelescopePlague doctor costumes—actually kind of a good ideaEventually, by the early seventeenth century, the idea that the plague was spread by infectious vapors in the air led to the development of the infamous plague doctor outfit. As I discuss in this article I published at the beginning of March 2020, modern people really love to make fun of plague doctors because they wore masks with beaks attached to them, but, in actuality, the plague doctor outfit really wasn’t a dumb idea at all.Basically, plague doctors wore suits and masks made of thick, waxed leather that left no part of their body exposed. The “beak” was filled with sweet-smelling herbs that were supposed to purify the air the plague doctor breathed to keep him from breathing in the miasmata. The idea was to create an outfit that the disease could not penetrate.This is basically the same idea behind a modern hazmat suit. The only difference is that now we have a better understanding of how diseases spread, so our hazmat suits are more effective than the ones plague doctors used in the seventeenth century.Plague doctors in the seventeenth century usually also carried a rod that they could use to examine sick people without having to go too close to them. As we all now know, maintaining social distance from people who are infected with a disease is generally a good idea.ABOVE: Photograph from Wikimedia Commons of a surviving seventeenth-century plague doctor mask from Austria or Germany on display in the Deutsches Historisches Museum in BerlinA little perspective about diseases today…We shouldn’t make fun of people in pre-modern times for not knowing everything that we know about medicine today. Today, most of us know that infectious diseases are caused by extremely tiny invisible agents known as “pathogens,” but this idea is not at all obvious or intuitive and, if you just judge it by how it sounds, it really sounds just as silly as anything anyone believed in the Middle Ages. We only know that it is true because of centuries of scientific observations and experiments. If not for our forebears, we would be just as clueless as people were a thousand years ago.Furthermore, there is still a lot that we don’t know about medicine. We have completely eradicated smallpox and nearly eradicated other diseases like polio, but there are a lot of extremely deadly diseases that we are still dealing with:The Centers for Disease Control and Prevention (CDC) currently estimates that the seasonal influenza results in somewhere between 9,300,000 and 45,000,000 illnesses, somewhere between 140,000 and 810,000 hospitalizations, and somewhere between 12,000 and 61,000 deaths each year in the United States alone.According to the World Health Organization (WHO), tuberculosis killed somewhere around 1.5 million people worldwide in 2018, making it one of the ten most common causes of death in the world and the most common cause of death from a single pathogen. It is estimated that roughly one quarter of all people in the world are currently infected with tuberculosis, but only somewhere between 5% and 15% of all people infected actually develop symptoms.According to the CDC, there were 16,350 deaths related to HIV in 2017 in the United States alone. While that is far lower than the number of people that were dying of HIV each year two-and-a-half decades ago, that’s still a lot of people.As of today, there have been 228,194 confirmed deaths from COVID-19 worldwide. The actual death toll is almost certainly much higher, though, due to large numbers of people who have died of the virus without ever being tested for it.These diseases and others are still killing tens of thousands of people all over the world every year—despite all our modern medical sophistication. We have come a long way, but we still have a long way to go.ABOVE: Photograph from Wikimedia Commons of Mycobacterium tuberculosis, the bacterium that causes tuberculosis, an ancient disease that still kills over a million people worldwide each year.A little more perspective about people today…Finally, I think I should emphasize that people today have all sorts of beliefs about COVID-19 that I think most people will agree with me are obviously false. For instance:There are people who think that you can kill the virus that causes COVID-19 by drinking bleach.There are people who think that you can cure COVID-19 by snorting cocaine.There are people who think that COVID-19 is caused by 5G networks.There are people who think that drinking boiled garlic water can protect you from catching COVID-19.There are people who think that masturbating can protect you from catching COVID-19.All of these beliefs are wrong, but they are all real things that people alive right now actually believe. Donald Trump, the president of the United States himself, has even lent credence to the idea that ingesting disinfectants can cure COVID-19—even though that actually kills people.Again, consider that before you decide to make fun of medieval people for being “so stupid and superstitious.” Quite frankly, modern people aren’t any better.ABOVE: Photograph from Wikimedia Commons of Clorox bleach bottles on a shelf at the grocery store. Contrary to what some people have claimed, drinking bleach will not cure COVID-19; instead, it will kill you because bleach is highly toxic.(NOTE: I have also published a version of this article on my website. Here is a link to the version of the article on my website.)