This is perhaps the best time of year to visit the Farmers Market, with the tables and baskets full of tomatoes, red peppers, and colorful squash gleaming in the sunshine. Many mid- to late summer favorites belong to three groups: the family Cucurbitaceae, the family Solanaceae (or the nightshades), and the genus Prunus, which is in the family Rosaceae. This is the first in a series of three posts that will appear this month on the names of these delicious edibles.

We’ll start with the Curcubitaceae because really, who doesn’t appreciate a good cucurbit? (It’s pronounced cue-CUR-bit, by the way.) They take their name from the Latin word for gourd and include the cucumber, summer squash (zucchini and yellow squash), winter squash, cantaloupe, watermelon, and pumpkin.

Squash, summer and winter, including pumpkins, are New World fruits that belong to the species Cucurbita pepo. Botanically speaking, they’re fruits, not vegetables, because they are essentially the ripened ovaries that develop from the plant’s flowers. Vegetables, on the other hand, are edible parts of plants that do not include the ovaries. In fact, botanists use the name pepo for a particular type of fruit, a berry with a thick rind and fleshy center, because it’s characteristic of this species.

Cucurbita pepo was one of the first plants domesticated in the Americas, upwards of 10,000 years ago. The English word squash derives from a Narragansett word, askutasquash. (The 17th century seems like yesterday when you put it in the context of 10,000 years of agriculture.) At a conservative estimate, there are a bezillion varieties within this species, so I’ll mention only one of my favorites. The zucchini was developed in Italy long after the species was introduced from the Americas; its name is the diminutive of zucca, for pumpkin or squash.¹ In France, the UK, and Ireland, it’s called a courgette, which is the diminutive of the French word for squash, courge.

Unlike the squash, the cucumbers and melons are Old World fruits. If you start to research the history of cucumbers, one of the first things you’re likely to learn is that the Roman emperor Tiberius was so enamored of Cucumis sativus, the cucumber that graces our tables today, that portable raised beds were used to make them available year-round. These contraptions were wheeled about to catch the sunshine and covered to protect the plants in cold weather. (Sativus, which means cultivated, describes plants that have been domesticated; we’ll see it in other names as well.)

This seems like a lot of work just to have cucumbers all year.² Tomatoes, yes, or basil, or raspberries, but cucumbers? Well, evidently yes, but probably not Cucumis sativus. A 2008 paper suggests that for centuries the word cucumis (and other terms in Greek and Hebrew) were erroneously translated or misunderstood. The evidence from written works and images of the time indicates that people living around the Mediterranean were actually eating what we would today call Armenian cucumbers (aka snake melon, snake cucumber, or “those big long ones you see sometimes at the grocery store”).

The Armenian cucumber is a variety within the genus Cucumis melo, which is mostly muskmelons. (Technically, it is a muskmelon, but it’s hardly a representative one.) The muskmelons, like the squash, come in a dizzying array of varieties, from the musky-smelling cantaloupe to the less fragrant honeydew (a member of the cultivar group Cucumis melo Inodorus). The species name melo ultimately comes from the Greek word melopepon, which combines the word for apple (melon) and gourd (pepon). (The name pumpkin also came indirectly from pepon.)

Watermelons, which differ markedly from the muskmelons, are another species entirely, Citrullus lanatus, which originated in Africa. Because the average watermelon contains more than 90% water, the source of the common name is obvious. Citrullus is probably derived from a Latin name for a type of cucumber (maybe we’re starting to chase our tails here). Lanatus, the Latin word for woolly, describes the hairy leaves and stems of the plant.

Next week we’ll continue our trip through the Farmer’s Market by looking at the nightshades. Bon appétit.

See Part 2: Nightshades and Part 3: Drupes.

1 The Italian words are actually zucchina (singular) and zucchine (plural); these words are feminine in gender. However, the masculine form (zucchino, zucchini) is also used in Italy. This information may be useful to those people who like to talk about having one spaghetto.^↩

2 I like cucumbers, but I can live without them in the winter. In 1917, Good Housekeeping responded to a reader’s question about whether cucumbers are safe to eat with even fainter praise: “There is not enough nutriment in cucumbers to make any fuss about, but they are a condimental substance and are perfectly wholesome when properly masticated.” (Vol. 65, July-December 1917) I think they’re not quite as nutritiously null as Good Housekeeping thought back then.^↩

Learn more:

• The Squash Glossary from The Nibble runs to three pages.
• The Melons page from the Cook’s Thesaurus lists a respectable number of melons.
• The entire 2008 paper on cucurbits in the Roman Empire is available.

Here in the middle of this bafflingly quiet Atlantic hurricane season, I thought I’d look at the words hurricane and typhoon. Both words refer to the same thing, a large tropical cyclone (that is, an organized low pressure system over warm tropical or subtropical water). Which name is used depends on where they occur (hurricanes in the Atlantic and parts of the eastern Pacific, typhoons in the western Pacific).

Hurricane is ultimately a New World word that has a fairly straightforward lineage, although it went through many different spellings (the Oxford English Dictionary lists 39) before finally settling down. When the Spanish encountered the native peoples of the Caribbean (specifically, the Taino of Puerto Rico and also the Arawak and Carib Indians) in the 16th century, they learned about the god of disorder who was thought to control the weather. Juracán was the Spanish spelling for the name of this god. This morphed into the Spanish word huracán. The word entered English with many variant spellings, such as harrycain and hurlecane, and eventually became hurricane.

Typhoon, on the other hand, is a very well-traveled word with a long pedigree. In Greek mythology, Typhon (whirlwind) was the name of a giant who was known as the father of the winds. The Arabic word tufan for a large storm may have been based on the Greek word typhon. At any rate, the word traveled east with Arabic-speaking invaders to India in the 11th century. Toofan is still used to refer to a large storm in India. Early European explorers may have gotten the word from Arab pilots; it entered the English language as tufan or touffon in the 16th century and was recorded as tuffoon in 1699. The Chinese had a similar-sounding phrase tai fung, for great wind. The further evolution of tuffoon into the current spelling, typhoon, may have been influenced by both the Chinese word and the Greek root.

Learn more:

• FAQ from the National Oceanic and Atmospheric Administration on hurricane lingo
• Tropical cyclone naming page from the World Meteorological Organization on the naming of individual storms
• North America has seen a couple of impressive extratropical cyclones (large cyclones appearing outside of the tropics) in recent years; this Earth Observatory post showcases one from October 2010.
• xkcd has a good hurricane name comic.
• Two good books on hurricanes are Isaac’s Storm: A Man, a Time, and the Deadliest Hurricane in History, by Erik Larson (find in library) and Divine Wind: The History and Science of Hurricanes, by Kerry Emanuel (find in library).

In my work as a science editor, I run across unfamiliar terminology. Sometimes it’s baffling, and sometimes it’s charming. Here are some recent examples of the charming kind.

Magnetic local time: OK, this one requires a bit of an intro. Universal Time (UT) is a timekeeping system in which the day arbitrarily begins when it’s midnight in Greenwich, England (at longitude 0°). Each location has its own local time (UT plus or minus so many hours) based on the difference between its longitude and that of Greenwich. The longitude lines used in this kind of timekeeping are part of a latitude–longitude grid that converges at Earth’s physical north pole. Similarly, you can make a grid of lines that converge on Earth’s magnetic north pole. Then the magnetic local time is midnight when your line of longitude faces away from the sun and noon when it faces the sun.

Petrichor: This lovely word describes the scent of rain on dry earth, which is an absolutely heavenly thing if you live in a dry climate. Certain plant oils (notably those of the creosote bush) are absorbed by the soil and stone of the desert floor and released into the air when it rains, along with another compound from the wet soil, producing the heady aroma. The word is derived from the Greek word for stone (petros) and the Greek word ichor, which was what the gods of Greek mythology supposedly had instead of blood. (The words petroleum and petrify can also be traced back to petros.) This scent lies behind the title of a beautiful book that Gary Paul Nabhan wrote about the Sonoran desert and the Tohono O’Odham people who live there: The Desert Smells Like Rain: A Naturalist in O’odham Country (find in library).

Crab and milliCrab: The Crab is a measure of the X-ray output of an astronomical source at a particular wavelength, pegged to that of the Crab nebula, a supernova remnant in the constellation of Taurus. Because the Crab nebula is a powerful X-ray source, milliCrabs (thousandths of a Crab) are often used.

Auroral chorus and dawn chorus: These are both radio waves that are naturally produced when energetic electrons are injected into in Earth’s magnetosphere; they can be converted into somewhat eerie singing sounds (chirps, hoots, whistles). The dawn chorus is most likely to occur around sunrise, and the auroral chorus is associated with aurorae. Curiously, both names can be traced back to Aurora, the Roman goddess of the dawn. The northern and southern lights (aurora borealis and aurora australis) were named for their beautiful subtle colors, which resemble those of sunrise.

Learn more:

• Must astronomers find a replacement for the milliCrab? This 2011 article from Physics World suggests they might because the X-ray emission from the Crab nebula varies too much to be a reliable standard.

Somewhere in Colleen McCullough’s Masters of Rome series of novels, I ran across a reference to a city called Magnesia. For some reason, those old names tend to start running around in my head whenever I encounter them, creating a pleasing atmosphere of mystery and antiquity (Illyricum, Cappadocia, Thrace, Ephesus…). However, when “Magnesia” starts running through my mind, a blue bottle labeled “Milk of Magnesia” usually follows soon after. This brings to mind the element magnesium and even the concept of magnetism, and I finally wondered if there was any connection. There is, and it goes like this.

Magnesia was originally a strip of land along the coast of Thessaly in eastern Greece. It was named for the Magnetes tribe who settled it. The origin of the Magnetes shades back into myth: Magnes and his brother Macedon were among the sons of Zeus who founded the various Greek tribes. When the Magnetes colonized other regions, they are believed to have founded two cities in Asia Minor, Magnesia on the Maeander and Magnesia ad Sipylum. Today Magnesia is a regional unit in Greece.

Magnets are named for Magnesia; the word originally came from magnítis líthos or Magnesian stone, which referred to what we now call magnetite. This is an iron ore that under certain circumstances can become magnetized naturally, producing a lodestone.  These natural magnets introduced humankind to magnetism. An alternate explanation, cited by Pliny the Elder, involves a shepherd called Magnes who observed the effects of magnetite when the nails in his shoes were attracted to the stone he was walking across on Mount Ida on Crete. However, I’m inclined to file this one under “legend.”

Along with magnetite, certain types of magnesium ores are found in Greece. Overall, magnesium is the eighth most common element in Earth’s crust by mass, and incidentally the eleventh most abundant by mass in your body. Although magnesium is so common, it’s rarely found alone because it’s very reactive. Magnesium also came by its name from its early association with Magnesia. (Note that magnesium itself is not magnetic.)

The element manganese traces its name back to Magnesia too. The name magnítis líthos for magnetite became magnes, and it shared this name with another black mineral identified today as manganese dioxide. The name manganese for the element eventually evolved out of magnes. Slippery thing, language.

Finally we come to milk of magnesia, a suspension of magnesium hydroxide in water that has a milky appearance. It became known as a treatment for digestive complaints in the 19th century, and in 1873, Charles Henry Phillips gave the name Phillips’ Milk of Magnesia to his magnesium hydroxide suspension, which was marketed as an antacid and laxative. The US Patent Office lists Bayer as the current owner of the trademark.

So there you go: from Zeus’s children to magnets to magnesium and manganese to a laxative. Think of ancient Greece the next time you see one of those blue bottles.

Learn more:

• Information on magnesium in the human body from the Linus Pauling Institute’s Micronutrient Information Center
• Newspaper clipping from the Stamford Historical Society giving a brief history of the Charles H. Phillips Chemical Co., which grew out of the work of C. H. Phillips in his Stamford, CT laboratory

Sometimes a name tells us about the way people used to think about something. An initial understanding or categorization may look odd or confusing in late of later findings, but a name may stick anyway because it has become so widely used. Here are a few examples from astronomy.

Planetary nebulae: These were named purely for a superficial visual resemblance, and they have nothing to do with planets. Planetary nebulae appear in small telescopes as faint disks, somewhat like planets. When they were first observed, no one knew what they were, any more than they knew that their friends the spiral nebulae were in fact vast galaxies separate from our own. Planetary nebulae are the gaseous shells thrown off by stars in our own galaxy as they near the end of their lives. It’s not as dramatic as ending up a supernova, but it’s a beautiful way for a star to go.

Population I, II, and III stars: This may sound like it describes a sequence of stellar populations where Population I is the oldest, but in fact they’re numbered depending on their composition, and Population I is the youngest. Young, I hasten to clarify, is a relative thing, and the sun, at 4.5 billion years old, is a Population I star. Stars in this classification have the highest metal content. To an astronomer, a metal is any element heavier than helium, which is not as perverse as it sounds because it marks an important distinction between the primordial elements and everything else, which was later synthesized in stars. So Population I gained its metals from the stars of a much earlier generation, Population II, which synthesized heavier elements during their lifetimes and spread them through the interstellar medium as they died. Population II stars are not pure hydrogen and helium, however, suggesting the existence of a hypothetical primordial metal-free Population III.

Early and late stellar types: The sequence of stellar types I mentioned in an earlier post (O B A F G K M) was once thought to represent a series of life stages that stars went through. Consequently, O, B, and A stars were identified as stars early in their life cycle, and K and M stars were considered old.  You still see references to early and late type stars, even though that evolutionary model is obsolete.

Big Bang: This was originally a derogatory term coined by astronomers who believed in a steady-state universe rather than the expanding universe that key observations in the twentieth century suggested. As the expanding universe theory became better supported by observations, the name Big Bang stuck, although it suggests an explosion rather than an expansion and is almost certainly not the name that astronomers today would choose to describe the theory.

Learn more:

• Science, Religion, and the Big Bang video from MinutePhysics explains why the name Big Bang is confusing.
• Articles on Population II and Population III stars from Universe Today

If you enjoy reading about history or reading old books—histories, books about science, even novels—you’ve probably encountered some of the wonderful old chemical terms that were in use before our current chemical notation was developed. Here are a few of my favorites:

• Aqua fortis and aqua regia: Two powerful acids, nitric acid and a mixture of nitric and hydrochloric acids. They translate as strong water and royal water, respectively; the latter comes from the fact that it could dissolve the royal metal, gold. Don’t mess with these “waters”!

• Vitriol: Another acid, sulfuric acid. The fact that this word is now used metaphorically to describe harsh criticism is perhaps a clue to how very corrosive such criticism can be. The word derives from an alternative form of the Latin vitreolum, the neuter form of the adjective vitreolus, or glassy, presumably because sulfuric acid is a viscous liquid that is colorless or pale yellow.

• Brimstone: Plain old sulfur. Looks kind of funny without “fire and” in front of it, doesn’t it? The sulfurous smell of gases venting from volcanoes may have inspired the use of this word to describe the torments of hell. The word comes from the Old English brynstán, or literally burnstone.

• 

  Plumbago: Graphite, one of the well-known forms of carbon. The word comes from the Latin word plumbum, for lead, because graphite resembles certain lead ores. Plumbago is also the name of a type of plant, aka leadwort. This name also derives from plumbum, perhaps because the roots of the plant turn the hands gray when they are handled, or because of a mistaken belief that it was efficacious against lead poisoning.

•  Sal volatile and salt of hartshorn: Ammonium carbonate, which was used as a smelling salt. I first encountered sal volatile in some old novel (probably in the context of a young lady withdrawing a vial of it from her reticule to aid a companion who was overcome by faintness, perhaps when she saw the gentlemen she esteemed heartlessly dancing with another). I had no idea what it was or how on earth it worked. All was made clear when I learned that it was the pungent odor of ammonia that brought young ladies back from their swoons. Aqueous ammonia was known as spirit of hartshorn because it was distilled from the horns and hooves of male red deer, or harts.

Learn more:

• Demo and discussion of aqua regia from Periodic Table of Videos (Watch gold dissolve! Well, in time lapse, anyway. This is a really cool series of videos.)
• How do smelling salts work? from Live Science

The International Astronomical Union announced recently that public input will be considered when names are assigned to “planetary satellites, newly discovered planets, and their host stars.” These public names will be distinct from the scientific designations, which I gather will follow the rules they always have. This seems as good a time as any to look briefly into the pleasures of astronomical nomenclature.

It seems to me that astronomical objects have a particularly complex and engaging nomenclature, but that may be just because my background is in astronomy. Stars and other objects may have more than one name (even if we stick to English rather than considering the names given in other cultures), and the brighter stars typically have multiple designations. Consider the star Vega. It’s a relatively nearby and bright star that appears as part of the summer triangle, a group of three stars forming a huge triangle that’s visible from early summer until well into the autumn.

It’s also called α Lyrae, which indicates that it’s the brighest star in the constellation Lyra. This name follows the system Johann Bayer set up early in the 17th century, in which the stars in a constellation are designated by Greek letters, from the brightest to the dimmest. Once people started taking a good look with telescopes, of course, they found far more stars than the Greek alphabet could cover, so other systems came into use, for example, Flamsteed numbers, from a catalog published by John Flamsteed in 1725. In this system, Vega is 3 Lyrae. So already that’s three names for Vega.

When I was an undergrad taking an observational astronomy class, one of our early exercises was to observe various astronomical objects identified by sometimes cryptic designators; the point was to familiarize us with the catalogs and other tools used by astronomers, as well as with the telescope. One of the objects we were asked to observe was HD 172167, which turned out, when the proper source was consulted, to be none other than our old friend Vega. In fact, this familiar star actually has 55 different monikers, most of them numbers in catalogs.

You’ll notice a certain creeping abstraction here. Vega is an interesting name with a history of its own (which we will probably go into another time). Lyra is a constellation with a tragic myth behind it. In this they resemble many astronomical objects, which are rich in legend and lore. Dubhe and Merak, the Guardians of the Pole; Algol (the ghoul); Antares, the rival of Mars; the Beehive Cluster; the Seven Sisters: They might almost be the titles of fairy tales or science fiction stories. But HD 172167? SAO 67174? HIP91262? Where did the romance go?

Actually, these seemingly opaque designators have a wealth of history and lore behind them too. An HD number, for example, indicates a listing in the Henry Draper catalog. Draper was a doctor and an accomplished amateur astronomer who clearly saw the potential of one of the new technologies of the time, photography. He made the first photograph of the spectrum of a star (Vega, no doubt chosen because it’s so bright). He was also the first to photograph a nebula (the Orion Nebula). His wife, born Anna Mary Palmer, assisted him with his astronomical work, and when he died, in 1882 at the age of 45, she established a memorial in his name to fund further astronomical research based on photography and spectroscopy.

The memorial funded a gigantic project at Harvard College Observatory: classifying stars according to their spectra. Edward Pickering led the project, in which many women participated. For example, Annie Jump Cannon performed the astonishing task of looking at well over a quarter of a million stellar spectra and assigning each star to its proper type. The system of stellar types that we now know, in which stars are classed as O, B, A, F, G, K, or M according to their temperature, from the hottest to the coolest, was still being developed, and Cannon helped resolve a disagreement between two competing systems. Overall, her work was a massive achievement.

Stars are, of course, only one kind of heavenly body. There are various types of nebulae, star clusters, and galaxies, each with a naming system and catalogs tabulating the cosmic inventory. As we look more closely at our own solar system, we’re finding smaller and more distant objects to both classify and identify by individual names. I hope to get into more of this in future posts.

For now it’s enough to say that the story is the same for them as it is for the stars: they have the equivalent of common names, like the Orion Nebula, and various official designations. Each drily abstract catalog number, from the more or less familiar Messier numbers that identify 100+ faint fuzzy objects, to the New General Catalog (NGC), which lists a much larger group of non-stellar objects, to the most specialized catalogs of heavenly bodies—each of these represents years of careful human labor, many resources, and many observations. Many human stories. I’m glad that the human touch is being added to the naming of extrasolar planets. But I also love the names we have now, which are often monuments to human dedication and imagination.

Learn more:

• Since I originally published this post, Dava Sobel has written a wonderful book about the women of Harvard College Observatory who worked on stellar classification: The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars (find in library).
• The IAU’s Naming Astronomical Objects page (which, I am amused to note, begins “Celestial nomenclature has long been a controversial topic.”)
• If you want to see a listing of all 55 of Vega’s identifiers, here’s the basic information for Vega in the SIMBAD Astronomical Database.
• The Classification of Stellar Spectra, by Jesse Allen (University College London site) gives a good overview. Wikipedia’s Stellar classification page is quite thorough and has some nice graphics.

Sometimes it’s fun just to see what you can figure out about something by knowing the Latin or Greek roots of its name. This is also a great way to spot connections between very different things. I was delighted, for example, to find out that the name of the rhododendron has a charming etymology. The rhodo part comes from a Greek word meaning rose or rosy. You can see this root in the name rhodopsin, the pigment in the eye that is sensitive to red light. (You may also have heard it called visual purple.) There’s also a beautiful pinkish stone called rhodochrosite. The dendron part is from a Greek root meaning tree. Thus we also have dendrite, a branch extending from a nerve cell in the brain. Put it together, and you have rosy tree, a pleasing name for this flowering shrub.

Or consider the chrysanthemum. The chrys part is from a Greek root chrysos, meaning golden, and anthemum comes from the Greek anthemon, which means flower: golden flower. Chrysos also contributed to the names of the minerals chrysolite (golden stone) and chrysoprase (which translates literally as golden leek). Chrysoprase is a greenish mineral, but the word was formerly used to refer to a yellowish-green gemstone. We also see chrysos in chrysalis, the golden case surrounding a pupa.

Years ago, I was hiking with my younger son when we spotted a Lycopodium, or club moss. I thought I recognized some roots in the name Lycopodium, so I spelled it out for myself. I guessed that the lyco part is related to the Greek word for wolf, and the pod part is related to the Greek word for foot. “Wolf foot?” I said to Patrick, puzzled. It turns out that the names club moss and Lycopodium both come from the way this plant resembles other things: a club or a wolf’s paw, respectively. The genus Lycopodium has been split up, and the species pictured below, Lycopodium digitatum, has since been reclassified as Diphasiastrum digitatum.¹

Several other plant names feature the lyco root, including a genus of grasses called Lycurus (the common name is wolfstail) and a genus of plants called Lycopus (a variant on wolf foot; cf. octopus, named for its eight feet). It also appears in lycanthropy, which refers to the wolf-man of folklore. The pod root also appears in arthropod; arthropods, that is, crustaceans and insects, have jointed appendages. At the risk of taking this thing too far, I will point out that you also see arth in arthritis, an inflammation of the joints, and arthroscopic surgery, which can be performed on any joint but is often done on the knee.

This game could go on indefinitely. There’s pachysandra, which has thick (pachy, from a Greek word) stamens (the male part of the flower, from the Latin root androus, meaning male). Maybe your mind has already jumped to the elephant, or pachyderm, with its thick skin. The horsetail fern is also called Equisetum, from the words for horse and bristle. I will leave it there for now, but we will be coming back to this sort of thing many times in the future.

¹ I owe Patrick a debt of gratitude not only for introducing me to Lycopodium but for keeping me up to date on its current classification and suggesting several other wolf-related plant names.^↩

Learn more:

• List of Latin and Greek words commonly used in systematic names from Wikipedia
• If you share my fondness for rhododendrons, you might be interested in the Rhododendron Species Botanical Garden in Federal Way, Washington.

When I think of the sciences, I first think of biology, physics, chemistry…the names of subjects you can take a high school class in. Here are some finer-grained specialties within those sciences.

• Tribology: This term was coined relatively recently to describe the science of surfaces in contact (friction, lubrication, and wear). It comes from the Greek verb meaning to rub. Whether you were aware of it or not, you’ve almost certainly experienced the triboelectric effect, in which a material gains electrical charge by being rubbed against another material (for example, when you shock yourself on a doorknob after shuffling across a carpet).

• Oology: This subfield of zoology deals with birds’ nests and eggs. The first two letters are pronounced as two syllables (oh–ah, roughly), and the word comes from the Greek root oion, meaning egg. The same root is ultimately the source of oolite, a type of calcium-carbonate-based rock composed of small spherical grains (which are also called oolites, or ooliths: egg stones).

• Somnology/hypnology and oneirology: Most of the roots I’m talking about here are Greek, but in the scientific term for the study of sleep, we have a choice of Latin and Greek roots. Somnus was the Roman version of the Greek god of sleep, Hypnos. Hypnology is also used to describe the science of hypnosis, and somnology seems to be more common among scientists. Interestingly, several phenomena related to sleep retain the hypno– root: hypnopompic and hypnagogic hallucinations. These harmless but sometimes terrifying events occur as you’re waking up or falling asleep, respectively. Oneirology is the scientific study of dreams; this one is from the Greek root oneiros, or dream.

• Pedology and edaphology: These two divisions of soil science come from the Greek roots pedon (soil or ground) and edaphos (ground or basis). Pedology considers the soil itself, and edaphology considers the soil as the home of living things. Pedon is ultimately derived from the word for foot, the soil being underfoot.

Happy weekend! See if you can work any of these into your conversations this weekend.

Learn more:

• Ten theories on why we dream from io9.com
• Modern applications of tribology from ASME
• Operation Easter: The hunt for illegal egg collectors, by Julian Rubinstein (I learned the word oology from this New Yorker article.)

One of the things I had to decide when I started this blog was how I was going to treat the word earth. Should I use earth or Earth? Do I need to use the word the?

It may seem that I’m taking the geek part of the title Science Word Geek far too seriously here, but if you’ll bear with me, I think I can explain how the most minute of minutiae can sometimes point to a shift in worldview.

Earth is the proper name of our planet. So of course you would simply say Earth, the way you say Jupiter or Saturn. But wait a minute, we don’t usually say just Moon or Sun: “the astronauts landed on Moon”? Nah, it should be the moon. In a nonscientific context, earth alone, lowercase, makes sense, for example, in the phrase down to earth. But there are lots of times where I might feel more comfortable using Earth, say to compare the topography of Earth and Mars. I think that will probably be the most common case on this blog, so I decided to use Earth.

I think the reason that the moon seems so natural and the earth doesn’t always seem quite right may be that I grew up knowing there were multiple moons in the solar system, so to me they seem inherently generic. Our moon is obviously one of many, and to me, it always has been. I think there’s no reason to believe we won’t someday find Earthlike planets around other stars, but until we do, Earth is singular and unique in a way the moon and sun are not. We have discovered super-Earths, but not earths. We’ve also found Jupiter-like and Neptune-like planets around other stars, but I think most people still capitalize Jupiter and Neptune in those cases. We even have subtypes: hot Jupiters, eccentric Jupiters (their orbits, not their personalities), and hot Neptunes, but I’ve seen hot jupiter rarely if at all (and I just now had to argue with autocorrect in order to use a lowercase j).

It seems to me we’re going through an interesting transition in how we view our universe, and we’ve been through this kind of shift before. For example, Oceanus was the name of the ocean believed to encircle the known world in ancient times, when a great deal less of the world was known. Now we don’t even think twice about the fact that there are multiple oceans on Earth, and we speak casually of methane oceans on Titan or a subsurface ocean on Europa.

Something similar had to have happened with the sun as we recognized that it was one star among many, and with the moon as we learned that other planets had moons, starting with Galileo’s telescopic observations of the four largest moons of Jupiter. More recently, in the twentieth century, Edwin Hubble resolved a lively debate about whether spiral nebulae were part of the Milky Way or were “island universes,” or as we would put it now, separate galaxies in their own right.

Hubble used images taken by the Hooker 100-inch telescope, which was able to resolve individual stars in the Andromeda Nebula, and applied a newly discovered relationship between the period of a certain type of variable star (how long it took to go from bright to dim and back again) and its intrinsic brightness. If you know the inherent brightness of a star and its brightness as viewed from Earth, you can calculate its distance. Hubble found that the Andromeda Nebula was in fact the Andromeda Galaxy, around 2,000,000 light years away, and far too distant to be part of the Milky Way. So the singular term Galaxy, which came from a Greek root meaning milk, became lowercase when it expanded to cover all of the other galaxies. Scientific papers still distinguish between Galaxy (our own) and galaxy (one of the others).

I’m delighted to be living in a time when we can see the same shift happening with regard to planets. There are enough known exoplanets that we can begin to classify them according to type of planet and even type of solar system. My iPad chirps at me every time a new exoplanet is added to the database—what a heady experience! It’s well worth the occasional editorial perplexity.

Learn more:

• Article from the Solar Center at Stanford about the people who were instrumental in figuring out that the sun is a star
• Astronomy Photo of the Day’s web page about the 1920 Shapley-Curtis debate about the nature of the galaxies and how the question was resolved
• I use the Exoplanet App, which is based on the Open Exoplanet Catalogue. The Exoplanet App appears to be available only for the iPad, iPod Touch, and iPhone. There are several exoplanet apps for Android, and I don’t know anything about any of them, so I will not comment.
• A New York Philharmonic broadcast in 1945 included an intermission feature in which Edwin Hubble gave a ten-minute talk about the state of astronomical knowledge at the time.