What Is A Hurricane?

I had a house full of kids, recently. My son’s friends came over, so that gave us four people under the age of eight running around my house. And as kids do, they talk. One of the children, a seven-year-old girl, was telling everyone else about the tornadoes and recent flooding in Texas. This got them to talking about storms, and soon enough my son stops and asks me a question.

“What’s a hurricane?”

Ah… a big storm? You’d think I would know more. I used to live in Maryland and, while we didn’t get hit with hurricanes the way that (say) Florida did, we still got them coming ashore. I’ve watched the rain hammer down and the wind howl, and then sat in the eye, and then watched the wind and the rain hit again. But it turns out I don’t have a clear idea beyond “a big storm”.

Fortunately, the National Hurricane Center of the National Oceanic and Atmospheric Administration() offers a lot more detail. According to them, a hurricane is one of four varieties of a “tropical cyclone”. A tropical cyclone is, of course, “a rotating, organized system of clouds and thunderstorms that originates over tropical or subtropical waters and has a closed low-level circulation.” These storms rotate counterclockwise in the Northern Hemisphere, and clockwise in the Sourthern Hemisphere. NOAA breaks tropical cyclones into four categories:

  • Tropical depression, a cyclone with maximum sustained winds below 39 mph
  • Tropical storm, a cyclone with maximum sustained winds of 39 – 73 mph
  • Hurricane, a tropical cyclone with maximum sustained winds of 74 – 110 mph
  • Major hurricane, a tropical cyclone with maximum sustained winds of 111 mph or more.

Confusingly, hurricanes are known as cyclones in the Indian Ocean and South Pacific Ocean, and as typhoons in the western North Pacific. Tropical cyclones have seasons, with the Atlantic hurricane season running from June 1 through November 30 and the Eastern Pacific hurricane season running from May 15 through November 30.

Intriguingly enough, the winds are not necessarily the most dangerous aspect of a hurricane. Storm surges get that award. These are swells of sea water 30 to 40 miles wide and up to 15 feet higher than the normal tide level that get driven ahead of the storms, acting like a miniature tidal wave when they hit shore.

Surf’s up!

How Do We Walk?

I don’t recall the circumstances of this question. It probably came up because I’ve been doing a lot of walking recently, in an effort to get myself healthy. But my son asked it. “How do we walk?”

That’s… that’s a really good question. A question that I don’t know I’ve ever contemplated before. I take walking for granted – I can walk, I watched my son learn to walk, it’s just sort of something we do. But, he’s right. How do we walk? I know that it has something do do with having bones (so our legs don’t collapse into puddles of meat when we move), and muscles (to move the legs), and balance (to keep us from tipping over). But… how does it all work?

The Brain

Unsurprisingly, everything starts in the brain. The whole brain, in a complicated series of feedback loops. Much of what follows is a “chicken and egg” scenario, but you can loosely think of the process as working like this:

  1. The decision to walk is made in the forward portion of the frontal cortex, which is also sometimes known as the “frontal lobes”.
  2. The frontal cortex and the sensory cortex (along with other portions of the brain) send impulses to the basal ganglia.
  3. The basal ganglia activates the motor cortex.
  4. The motor cortex signals the cerebellum about the intended movement.
  5. The cerebellum takes information from the motor and sensory cortexes, and then provides the motor cortex with the direction, force, and duration of movement.
  6. The motor cortex sends commands to the muscles through the spinal cord.
  7. The muscles contract.

Simple, right? Well, more like simplified. A more detailed look at the process can be found on Brain Connection in The Anatomy of Movement. Suffice it to say that there is a lot going on in your brain when you move, and I’ve barely scratched the surface of it here.

Mechanical motion

It’s not all just the brain, though. If it was we’d have grey and white matter instead of muscle and bone. And it turns out that there have been a number of studies about human walking, in order to be able to build robots that walk like humans and in order to develop better prosthetics. I’ll be drawing from three articles from the Journal of Experimental Biology in discussing the mechanics of walking:

Human walking involves a relatively stiff-legged gait, comparable to pole-vaulting. Our center of mass rises as we push off to take a step and lowers when our heel hits the ground. Although we usually think of our muscles as doing the work of walking, by contracting when the leg is in the air and then extending when the foot hits the ground, our tendons are actively involved as well. They help store energy in a similar fashion to springs, by stretching as the leg bears the weight of supporting the body and then recoiling when the foot pushes off, amplifying the efforts of the muscles as they contract. This boost from the stored energy in the tendon actually gives our legs more power than they could generate with muscle alone.

A forward shift in body weight helps with walking as well. You lean forward slightly as you walk, meaning your weight slightly pulls you in the direction you want to travel. The faster you move, the more you lean forward – meaning your legs have less mass to work against. Then, as you slow, your body returns to a more upright stance.


What, then, keeps us from falling over? Our brains, of course, drawing on signals from our ears.

The National Institutes of Health’s page on Balance Disorders discusses this in some detail. We have something called the vestibular system, which is primarily a structure in the inner ears called the labyrinth. The labyrinth contains the semicircular canals, the utricle, and the saccule. These organs combine to tell your brain which way your head has moved, the position of your head with respect to gravity, and whether your head is moving. This information feeds into your sensory cortex, and gets incorporated into the feedback loop described above.

So, how do we walk? Through an extremely complicated process of neural and muscular activity. It’s fascinating stuff, and probably something you shouldn’t think too hard about while walking.

Why do you guys wear glasses?

I wear glasses, and have since I was… eight, I think. For a while, to say the least. And when I was small, I was fascinated by my parent’s glasses. I’d put them on, once in a while, and marvel at how – even though I wore glasses and my mom and my dad also wore glasses – the world looked so different and so strange through their glasses.

I think this must be a universal thing, because my son is fascinated by the glasses my wife and I wear. He doesn’t need them right now, and I hope he never will, but he’s fascinated by them. And every once in a while, I’ll let him try mine on. He peers through the lenses, his eyes magnified and looking huge, and then he’ll take them off and hand them back. One time when he did, he looked at me and asked “why do you guys wear glasses?”

Well, I wear them specifically because I’m nearsighted and have astigmatism. My wife wears them because she’s nearsighted as well. So was my mom, terribly so, but my father was farsighted. So I explained to him that my eyes don’t work right, and the lenses let me see better. His response? “Why?”

Good question.


Nearsightedness is medically termed “myopia”. It comes from the Greek myōpía meaning near-sighted (literally “to shut eye”). According to the American Optometric Association, it “is a vision condition in which close objects are seen clearly, but objects farther away appear blurred. Nearsightedness occurs if the eyeball is too long or the cornea, the clear front cover of the eye, has too much curvature. As a result, the light entering the eye isn’t focused correctly and distant objects look blurred.”

Approximately 30% of the US population suffers from myopia. The tendancy to develop myopia is inherited, but the development is also affected by doing intense close visual work such as reading or working at a computer. The AOA notes, however, that you generally cannot become nearsighted just because you read – the actual onset of the condition is a combination of both genes and environment.


Farsightedness, by contrast, is medically termed “hyperopia”. It derives from the Greek hyper (over, above) and the Greek -ōpia (view, look). According to the American Optometric Association, it “is a vision condition in which distant objects are usually seen clearly, but close ones do not come into proper focus. Farsightedness occurs if your eyeball is too short or the cornea has too little curvature, so light entering your eye is not focused correctly.”

Unlike myopia, the AOA does not give any figures about how many people in the US suffer from hyperopia. The do note, however, that “common vision screenings, often done in schools, are generally ineffective in detecting farsightedness. A comprehensive optometric examination will include testing for farsightedness.”


Astigmatism or astigmia is the medical term for a “vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye. An irregular shaped cornea or lens prevents light from focusing properly on the retina, the light sensitive surface at the back of the eye. As a result, vision becomes blurred at any distance.” It derives from the prefix “a-” (not or without) and the Greek stigma (tattoo mark), so I’ll be honest and say I don’t understand the derivation of the word at all.

The AOA notes that astifmatism is an extremely common vision condition. Most people have it to one degree or another, but most don’t have it to a degree that it impacts vision.

How Glasses Work

All of these vision problems keep your cornea – the lens at the front of your eye – from focusing light properly on your retina. A healthy eye has the focus on the retina. With myopia the focal point falls in front of the retina, and with hyperopia your focal point falls behind the retina. And astigmatism just makes the focal issues worse. So the lens of the glasses simply changes how the light enters your eyes, adjusting your focal point to fall on the retina once more.


“Simply”.  Yeah, you have to love how our understanding of optics has advanced to the point that we can regard this as a “simple” process.

Do Earwigs Go In Your Ear?

As we generally do, I let my son pick out his bedtime story. He chose Once There Was a Tree, which turned out to be a fascinating little story about a tree getting cut down and then all the different animals that made use of the stup for various purposes. Quite well done, and the art is mostly extremely good. But there’s one passage that reads:

The warm sun dried the tree stump, and soon a new occupant had moved in – an earwig. Liking nothing better than the shade, he crept under the bark to sleep.

First, my son asked me what an earwig is. I had no idea, and the illustration in the book didn’t make it very clear. Second, my son – riffing off the name – asked me if earwigs go in your ear. Without knowing for sure, I said “no”. There are just some things you don’t want your five year old thinking about too hard right before bed. But I have no certain knowledge that this is true. So, here we go.

To begin with, this is an earwig:


So, yes. That picture, combined with a name like ‘earwig’, is terrifying. Wehn you dig into the meaning of “earwig”, it doesn’t get any better. According to Dictionary.com, the name comes from the “Middle English erwigge, Old English ēarwicga ear insect; from the notion that it enters people’s ears”.

According to the PennState College of Agricultural Sciences Department of Entomology, there “are twenty-two species of earwigs in the United States, twelve of which have been introduced from other countries”. Their article focuses on the European earwig (Forficula auricularia), which is “considered one of the most important earwigs since large numbers of them may seek shelter in homes and consequently become a notorious household pest”.

The European earwig was introduced to North America some time in the early 1900’s, and was first observed in the United States in 1907. They tend to be 5/8 inches long, with forceps ranging between 3/16 inch and 3/8 inch. Those forceps are used both for protection and to capture prey. They can fly, but rarely do, and they prefer to hide in dark, most crevaces. They’re omnivorous, eating most any plant matter and other insects.

Iowa State University, on their Earwigs page, addresses the question of whether or not they crawl into human ears:

Earwigs are a fairly well-known insect, from folk lore if not from actual experience. The earwig is the insect reputed in superstition to purposefully crawl into the ears of sleeping persons for the purpose of burrowing into the brain to lay eggs. Of course, there is no truth to these tales, though earwigs, like moths, beetles, cockroaches, ants and flies may wander into our ear canals by accident.

So, they might. But if they do, it won’t be any more deliberate than any other insect that crawls into your ear. I’ll leave it up to you to decide how comforting that is.

But if they don’t crawl into your ear so they can burrow into your brain and lay eggs, are they dangerous? The short answer is, “not terribly”. Not to people, anyway. Orkin, a pest control company here in the United States, has this to say on the subject:

Many people wonder if earwigs will bite people. The pincers are used for defense and if picked up and agitated, the earwig will exercise the use of the forceps. These are not stings or bites, though, which are terms used for insects with stingers or biting mouthparts. Even in extreme cases of large forceps of adult males, the pinch can be painful but there is no venom and the pinch rarely breaks the skin.

In the event that the pinch does break the skin, it is best to utilize the same first aid as one would use for any type of scratch. Keep in mind that earwigs do live in the soil typically, so there is the possibility of germs getting into the cut from the forceps. So, if there is a cut or open sore, or if the earwig pinch breaks skin, use a proper antibiotic lotion or cream. There is no telltale “bite mark” unique to an earwig as they do not hurt people. If there are medical concerns, speak to a medical professional.

So no, they don’t bite. They’ll just shank you with their tail pincers if you pick them up. And they won’t burrow into your brain through your ear. So really, you can stop worrying about that and start worrying about the eight spiders a year that it is claimed you eat in your sleep.

That’s not true either. But try and convince yourself of that tonight.

A couple of quick updates…

I’ve modified a couple of posts.  First off, National Geographic weighed in on How Mistletoe Became Everyone’s Favorite Parasite.  You can read about it by clicking the link, or by checking out the addendum to What’s Mistletoe?

There’s a couple of updates about Water Bears as well, as it turns out they are both more and less weird than I thought.  They probably aren’t rampaging DNA thieves, but they do secrete glass.  Check out those links, or read the update to Pangolins and Water Bears, Oh My!

Happy Holidays, everyone!


What’s Robin Hood’s Last Name?

Some questions just come out of left field.

My son’s been mildly obsessed with Robin Hood, ever since we first watched the Disney animated Robin Hood movie. Not to the same degree he’s obsessed with Star Wars, mind, but it’s still his go-to cartoon movie. I could imagine any number of questions coming out of that film – Why the characters aren’t wearing pants, perhaps. Or why are they animals. I even got one of the questions I expected: “Why is Prince John putting them in jail?” But I never expected to get asked:

“Dad? What’s Robin Hood’s last name?”

Seriously. If I’d even considered that as a question, I’d have expected him to think “Hood” was the character’s last name. Heck, I even tried that as an answer.

“His last name is Hood.”

“No it’s not, daddy. That’s not a last name.”

Go figure. So, it’s off to the internet. And the short answer to the question is that he probably doesn’t have one, because there probably isn’t a historical Robin Hood. As Stephen Knight and Thomas Ohlgren write in the introduction to Robin Hood and Other Outlaw Tales:

It remains an item of faith, or perhaps obsession, among many modern commentators that Robin Hood too was a real person, and they believe that enough careful attention to the records will produce a real Robin Hood who might, like the equally obscure King Arthur, be the real figure behind the myths — or legends, as such historians would want to call them. It is true (and usually ignored by the modern historians) that the earliest references to the hero all assume he was a real person amplified in story, an English Wallace, it might seem, especially because the earliest chroniclers who mention Robin are all Scottish….

That idea of antiquity and the prolific appearance of the name do not, however, suggest that there was one “original” Robin Hood, but that by then the name refers generally to someone who was in some way outside or against the law as it was being imposed.

Interestingly enough, however, there are sources that provide him with a name. For example, there’s Joseph Ritson’s Robin Hood: A collection of all the ancient poems, songs and ballads, now extant, relative to that celebrated English outlaw:

ROBIN HOOD was born at Locksley, in the county of Nottingham, in the reigh of King Henry the Second, and about the year of Christ 1160. His extraction was noble, and his true name ROBERT FITZOOTH, which vulgar pronunciation easily corrupted into ROBIN HOOD. He is frequently styled, and commonly reputed to have been, EARL OF HUNTINGDON; a title to which, in the latter part of his life, at least, he actually appears to have had some sort of pretension.

BBC History weighs in as well, with the following quote from Robin Hood and his Historical Context:

On 25th July 1225, the royal justices held an assize at York. When the penalties were recorded in the Michaelmas roll of the Exchequer, they included 32s. 6d. for the chattels of one Robert Hod, fugitive. The account was carried forward into the following year, when he had acquired the nickname of ‘Hobbehod’, and indicates that he had been a tenant of the archbishopric of York.

The article notes, however, that the evidence for this is flimsy. John Major, the historian who presented the argument, used dating described by the author as “purely arbitrary”. However, it does fall nicely within the reign of King John, so that’s one bit of evidence in favor of Robert Hod being Robin Hood’s real name. (And incidentally, don’t you love how historians snipe at each other?)

Robin Hood may or may not have been real, and his name may or may not have been Robin Hood. But real people were certainly happy to adopt his name as their own. As the BBC article goes on to discuss:

The King’s Remembrancer’s Memoranda Roll of Easter 1262 notes the pardoning of the prior of Sandleford for seizing without warrant the chattels of one William Robehod, fugitive. This case can be cross-referenced with the roll of the Justices in Eyre in Berkshire in 1261, in which a criminal gang is outlawed, including William son of Robert le Fevere, whose chattels were seized without warrant by the prior of Sandleford.

This William son of Robert and William Robehod were certainly one and the same, and some clerk during transcription had changed the name. It follows that the man who changed the name knew of the legend and equated the name of Robin Hood with outlawry.

The article further notes that “there are numerous cases in the C13th & C14th of outlaws deliberately taking on the pseudonyms of Robin Hood and Little John, and it seems likely that the original Friar Tuck who got accreted to the legend was one Robert Stafford who was active in Sussex between 1417 and 1429.”

So Robin Hood’s real name may have been Hod. Or Fitzooth. Or nothing at all.  But, whatever it was, he’s still famous.

How Many Snowflakes Does It Take To Make A Snowman?

Far from being a white Christmas around here, things are shaping up to be a sort of greyish-green muddy Christmas. I’m disappointed, my son is disappointed, and my wife is thrilled – she doesn’t like snow. But we did get a few flurries last week. At that time, my son stood at the sliding glass door of our condo and stared out. “It’s snowing, daddy!”

“I know,” I say, looking up from my book.

“But it’s not enough to make a snowman,” he adds, sounding a little disappointed.

Glancing outside, I see that there isn’t even enough snow to dust the ground. It’s melting before it lands, in some cases. “No,” I agree, “there isn’t.”

“It’ll take six million!” he declares. “Seven, eight million!”

At this moment, I’m pretty sure I see where he’s going with this. But I ask anyway. “Eight million what?”

“It’ll take eight million snowflakes to make a snowman!”

Well, that’s not precisely a question. But I’ll run with it.

It turns out that there are a few ways to figure the answer. For laughs, I tried punching the question “how many snowflakes in a snowman” into Wolfram Alpha. Believe it or not, I got an answer: an average of 58 million (5.8 x 107), with a range of 54 million to 61 million (5.4 x 107 to 6.1 x 107). The calculations assumed that a “typical snowman” could be modeled by a cylinder with a volume of 40 cubic feet, and that a snowflake could be modeled as a sphere with a volume of 0.0000004 cubic feet (4.0 x 10-7) and a packing density of 0.56 to 0.64.

Another way to do this is to figure out the mass of a snowflake. Amusingly enough, The Physics Factbook actually has an entry titled Mass of a Snowflake. It tells us the following:

  • The mass of a water molecule is 2.992 x 10-26 kg.
  • A typical snow crystal may contain 1018 water molecules.
  • A typical snowflake is made of 100 snow crystals

The end result is that a typical snowflake weighs about 3 mg. There’s 28.3495 grams in an ounce, which is the same as 28,349.5 mg, so that gives us 9,449.8 snowflakes per ounce. There’s 16 ounces in a pound, so that gives us 151,197 snowflakes in a pound of snow.

Here’s where it gets tricky. As far as I can tell, there is no such beast as a “regulation size snowman”. So I’m going to do a lot of estimates here. Let’s assume a three-tier snowman, with the middle tier about two-thirds the size of the base, and the top tier about half the size of the base. And let’s assume my son is building it. My son weighs 49 pounds, and 15-20 pounds seems to be about the limit of what he can lift without help. So, let’s assume he starts by making a 18 pound base (near the upper end of what he seems to be able to handle, because rolling is easier than lifting). That gives him a 12 pound middle and a 9 pound top. So, 39 pounds of snow in all. 39 times 151,197 gives us 5,896,696 snowflakes. Less than the Wolfram Alpha estimate, yes, but I don’t think my son’s snowman is 40 cubic feet of snow, either.

Interestingly enough, he’s not far off from his own estimate of six to eight million snowflakes. Eight million snowflakes would only add another 13.9 pounds (2,103,304 snowflakes/151,197 snowflakes) to the snowman. That would give us a snowman with a 24.4 pound base, a 16.3 pound midsection, and a 12.2 pound head. It might be slightly tough going for my son, but I suspect he could still build that.

For laughs, the hypothetical 39 pound snowman is composed of 589,668,300,000,000,000,000,000,000 water molecules. Numbers like that are the clearest explanation of why exponents were invented.