Monday, August 25, 2014

Apple #682: Dog Days of Summer

It has finally turned humid this summer.  For weeks and weeks, the weather has been beautiful -- sunny, breezy, warm, and none of that oppressive humidity.  But a few days ago, we had a big fat thunderstorm, and it left a lot of that humidity behind.  Looks like it won't budge for the whole week, either.

Which makes me think, we have finally entered the Dog Days of Summer.

What does that mean, anyway?  I have always imaged it means this:

(Photo from Doggie Cakes)

(Photo by Snowlight at Flickr, sourced from Low Country Dog)

(Photo from The Pet Wiki)

The Dog Days of Summer: when the weather gets so hot, all the dogs are panting.

But no, that is not the correct definition.
  • The Dog Days refers to the position of Sirius, the dog star (No, not Sirius Black), relative to the sun.

Sirius is the brightest star in the constellation Canis Major (Bigger Dog). It's just below Orion -- the 3 stars of Orion's belt point to it.  The story goes that Canis Major is Orion's hunting dog.
(Image from

  • Ancient Romans noticed that during the hottest time of the summer, the brightest star in the night sky -- Sirius -- was rising and setting roughly the same time as the sun. 
  • Some people say the Romans thought that Sirius's conjunction with the sun was adding heat to the days, and that's why those particular days were hotter.  
  • In reality, while Sirius is the brightest star in the sky, it is much too far away for its heat to have any impact on us.  

Sirius is larger and brighter and hotter than our sun -- though it's too far away for us to feel its heat.
(Image from Astro Bob)

  • The Romans were pretty smart cookies, though, so they may have known this and simply been aware that the two were in the sky at the same time. 
  • Ah, yes, here we are.  An astronomer named Geminus wrote, around 70 B.C., "It is generally believed that Sirius produces the heat of the 'dog days,' but this is an error, for the star merely marks a season of the year when the sun's heat is the greatest." 
  • (So, Weather Channel and everybody else, quit making the Romans out to be a bunch of dummies.)
  • Knowing that the two stars were in the sky at the same time, the Romans named that stretch of days the Dog Days of Summer. (Actually, the time period goes from about 15 days before the two rise together through 15 days after)
  • Exactly what part of summer that happened is also now in question.  Because of the very slow change in the Earth's orientation on its axis, when Sirius rises with the sun now is slightly different than when it rose back then. 
  • Some say it used to happen from July 23 though August 23, or thereabouts.
  • Now, however, the Farmer's Almanac says the Dog Days officially happen each year from July 3 through August 11, and everybody more or less goes along with that.
  • You kids with your smart phones, you've probably got an app that allows you to point your phone at the sky and it will tell you where the constellations are.  If you don't, this app called Star Walk ($2.99) supposedly does just that. Get an app like this, and you can see for yourself where Sirius is, and whether we're actually in the Dog Days or not.
  • (I know, he fell through the portal and he isn't coming back.)

Monday, August 18, 2014

Apple #681: Airport Runway Signs

I have had a request!  Daily Apple reader Jamarcus wants to know, what do all those signs next to airport runways mean?  You know, the ones that look something like this:

This sign lights up so it will be visible to pilots at night. But what do the letters and numbers mean?
(Photo and sign from Astronics Corporation)

A very good question.  Something I have often wondered myself.

Before you can interpret the signs, it helps to know how things get named at airports.


  • There are taxiways, and there are runways.  Runways are the paved strips where planes take off and land.  Taxiways are the paved passageways the planes take to get from the terminal to the runway to take off, or from the runway where they've landed back to the terminal.
  • You definitely want to keep the two separate because you don't want one plane ambling down a runway as another plane is about to land there.
  • A lot more real estate is covered by taxiways.  Some of our airports are enormous, and a plane may have to travel quite a long way to get from the terminal gate out to the runway.  It will have to drive down a lot of taxiways before it gets to the runway.
  • Taxiways are indicated with letters, beginning A, B, C, etc.  All airports begin their naming of taxiways with A, and one taxiway can go for a really long way. So the signs you see from your airport window will most often have an A on them.  
  • Some airports are so big or have so many taxiways, they get up to G.  Theoretically, taxiways could be lettered all the way up to Z, and then get the letters doubled: AA, BB, CC, etc.  But in real life, it's rare that taxiways are named much deeper into the alphabet than G.
  • Taxiways can never be named H.  The letter H is reserved for helipads -- landing places for helicopters.
  • They can also never be named I or O, because those letters could be mistaken for numbers.
  • They can also never be named X because an X on a sign means the runway or taxiway is closed.
  • You will often see signs that combine a letter and a number, such as A1, or B3 (as above), or C2.  These indicate either:
    • a stub taxiway -- a connector that goes from a runway to a taxiway that runs parallel to the runway (a little cross-bar connector from a runway to a taxiway) 
    • or the exit or entrance connector that goes from a taxiway to & from the terminal. The connectors get named sequentially A1, A2, A3, etc. along the length of the taxiway.
  • Keeping all those rules in mind (and a few I've left out for brevity's sake), an airport also needs to make sure no taxiway has a name that could be confused with a runway, and no two taxiways have the same name. 

Well, this is hard to see. But the runways have the dashed lines, and the taxiways are thinner.  The taxiways are named, from top to bottom, A, B, and C, and the little connectors that go between the runways and the taxiways are named, from left to right, A1, A2, A3, A4, A5, A6, and A7, and then in similar fashion for the connectors that go off taxiways B and C.  The little taxiway that goes vertically, bisecting the runways and the parallel taxiways, is named J.  That one gets its own letter, as opposed to something like C5, because that's a high-traffic taxiway.
(Diagram from the FAA's Engineering Brief on Taxiway Nomenclature)

This isn't a real-life runway but a screen shot from a simulator, but it does the job for our purposes.  The runway is on the right, as indicated by the white markings. The taxiway, outlined in yellow, is on the left.  A taxiway stub connects the two.  The colored paint and types of markings is a whole other set of visual indicators for pilots.  
(Photo from SimFlight)

  • By the way, the names of taxiways are not pronounced as the letters (A, B, C), but by the names that correspond to each letter, according to the NATO phonetic alphabet (Alpha, Bravo, Charlie).   So taxiway A2 would be called "Alpha two."
  • Yes, this is the same alphabet popularized by Wilco's Yankee Hotel Foxtrot.


  • Runways get named using numbers.  The thing that determines which numbers get assigned to a runway is where the runway is relative to points on a compass.  Then it gets turned into a kind of code.
  • North, South, East, and West all correspond to degrees on a compass.  North = 360°, for example.  According to this runway code, you lop off the 3rd digit of the compass point.  So if a runway were pointing true north, it would get numbered 36.  For the 4 points of the compass, the code works like this:
    • North = 360° = runway number 36
    • South = 180° = runway number 18
    • East = 90° = runway number 9
    • West = 270° = runway number 27
  • But of course it's rare for a runway to be heading in exactly the position of one of the points of the compass.  So in most cases, the runway number is arrived at by rounding off ±5°.  Let's say a runway is heading 176°.  That's within 5° of 180°, so its runway number would be 18.
  • It is also of course likely that a runway won't fall within 5° of one of the ordinal points on a compass, so it is very likely that runways will be named other numbers besides these four.
  • Because there are only 360° on a compass, you can't have a runway with a number higher than 36.  Also, since North is indicated by 360°, there is no 0°, so there will be no runway named 0.
  • Finally, because you may be allowed to land on a runway from either direction, its name will often be expressed from either approach direction, as in ##-##.  The first number indicates the compass direction from one end of the runway, let's say, 22.  That means the runway's compass heading is 220° (or within ±5° of that).  So the second number will be 180° from 220°, which is 40°, which becomes number 40.  This runway's official name is therefore 22-40.
  • By the way, the runway numbers are not pronounced the way we normally pronounce two-digit numbers. They are said individually.  Not "runway twenty-two" but rather "runway two-two." Nine is pronounced "niner."  Yes, just like in Airplane!


  • Now that you know what the letters and numbers mean, let's look at some signs.

(Photo and sign from Astronics Corporation)

  • This is our sign from earlier.  Now we know that B means "Taxiway Bravo" and B3 indicates a taxiway stub or connector or exit.  Anything in a black box with a yellow outline means "this is where you are."  So this sign means "You are on Taxiway Bravo. Taxiway stub Bravo three is to the right."

(Photo and sign from Astronics Corporation)
  • Here's another one. This means "You are on Taxiway Alpha.  Taxiway Foxtrot is to the left or angled to the right."

(Image from Avery Dennison)

  • Let's try a little more complicated one.  This one means, You are on Taxiway Hotel 3, Taxiway Charlie is to the left, Taxiway stub Charlie two is angled to the upper right, and more of Taxiway Charlie is to the right.
  • The red circle with the white line through it means "CLOSED."  This sign seems to be saying a little too softly that Taxiway stub Charlie two is closed, but that's what it means.  
  • (I think in this case, Avery Dennison, a label-making company, is saying you could put one of our  temporary "CLOSED" sticker on your runway signs.  Really, the airport should put up a giant CLOSED sign and they're also supposed to paint big red Xs on the ground before a closed section.)

This is what a CLOSED, or NO-ENTRY sign should look like. Either this or a gigantic X. Big and obvious. No subtlety. 
(Image from the Aircraft Owners and Pilots Association

  • Those yellow signs are the kinds you see most often. Taxiway Alpha's exit is this way, etc.  Now that you've got those down, you'll be able to interpret most of the signs along the taxiways that you'll see from your airplane window.
  • But there may be other signs in other colors and letters.  What about those?

(Image from Holland Aviation)

  • By now you know the part in the black box means "You are currently on Taxiway stub Sierra six."  The stuff on the right you might guess indicates a runway named either "two four or zero six." You are correct about that, but since it's in red, it also means a whole other thing.
  • Red signs mean "stop" or "holding position."  This means the plane has to stop right here and wait until it gets the go-ahead from air traffic control to proceed onto the runway.  There will also be some yellow & black markings like crazy on the pavement next to the sign.  The plane is absolutely not to cross those yellow and black lines at all until the pilot gets the OK.

(Photo from Airchive)

  • What about this one?  It's a red sign, so you know it means stop, but there are no numbers on it, only the letters ILS.  That can't mean a taxiway, right?
  • Right.  ILS stands for Instrument Landing System.  This is the signalling system used by air traffic control to give pilots precise information about taking off from a runway, or landing on it.  The red ILS sign means this is a critical ILS zone, and "stop here and wait or you will interfere with ILS signals being given to planes taking off or landing on this runway."

(Image from the Aircraft Owners and Pilots Association)  

  • You might also see a red sign with two runway numbers followed by the letters APCH.  That stands for "Approach."  Like the ILS sign, this means you've entered the approach for a particular runway (runway 15, in this case), and you must wait here so you don't interfere with the ILS signals for incoming planes.

(Photo from Air News Times)

  • This image is kind of dark, but anyway, what does FBO mean?  That's not a taxiway either, right?
  • Right.  FBO means "Fixed-base operator."  It's basically the gas station for airplanes.  FBOs are typically businesses that operate independently of the airport -- Chevron, or Philips 66, or some other gas company -- but that serve airplanes at the airport.  They provide fuel for the planes, and they also may provide maintenance services, hangars, parking, equipment rental, and so on.  They are used most often by people who fly their own planes.

(Image from the Aircraft Owners and Pilots Association

  • This one you don't see very often, but MIL means a military installation is that way.
  • I think that about covers it.  Thank you for flying with the Daily Apple today.  Enjoy your destination.

FAA, Airport Marking Aids and Signs
FAA Engineering Brief No. 89, Taxiway Nomenclature Convention
Jim Sweeney, The Short Course: Airport Signs
Aircraft Owners and Pilots Association, Airport Signs and Markings
Nevada DOT, AOPA's Airports Signage & Markings (this uses the terms runways and taxiways interchangeably, which is very confusing)
AOPA's runway flash cards
Bangalore Aviation, Airport runways: All you wanted to know but were afraid to ask
Sploid on Gizmodo, This is what all the signs and symbols at the airport runway mean
Alpha Bravo

Monday, August 4, 2014

Apple #680: Henna Tattoos

This weekend at the state fair, I got a henna tattoo.

I went for a simple $8 design of a sun. The tattoo artist offered to extend it so it goes up my finger. I said OK by me.
(Photo by the Apple Lady)

Naturally, I asked the woman who gave me the tattoo all sorts of questions about it.  And again naturally, I have still more questions.  So here follows some of the things she told me mixed in with some of the things I looked up and have learned since.

What Is Henna?

  • Henna is a dye made from the ground-up leaves of the henna plant (Lawsonia inermis).  
  • It's sometimes also referred to as mehndi or mehandi or mendhi.

The henna plant is a pretty non-descript looking shrub.
(Photo from Sailu's Kitchen)

  • The plant is a flowering shrub that grows in all sorts of places, including the US and Australia, but it's most prevalent in the dry, arid regions in northern Africa, India, and the Middle East, and it also grows in Southeast Asia.
  • The leaves themselves won't stain anything; you have to crush them or grind them up before they will work as a dye. Most people make their henna dye from powdered henna.
  • Henna has been used as a dye for both hair and skin for centuries in several different cultures & religions in the areas where it grows.
  • Though people of Muslim, Hindi, Jewish, and other faiths have all used henna, they all generally consider that henna tattoos mean some sort of good luck or blessing. 

Traditional bridal mehndi -- henna tattoo on the hands & wrists prior to a marriage, here, on a bride from India.
(Photo from Sameera Threading)

Why it's Usually Brown, and Why on the Hands & Feet

  • Traditionally in most of these cultures, women's hands or feet, or both, were tattooed before a wedding as a way to invoke good luck for the bride or the marriage.  But now lots of people get henna tattoos for lots of purposes.
  • It takes a while for the henna stain to sink into the skin.  So you don't know right away how dark the tattoo will be.  The stain can range from tan to light brown to auburn to dark brown.  
  • What color the tattoo becomes depends on the person's skin, where on the body the tattoo is applied (some areas take up the stain better than others), how much henna is present in the stain mixture, whether the henna artist has used some form of mild acid like lemon juice or vinegar as an adjuvant, etc. 
  • Because the color of the stain varies from one person to another and from one application to another, the darkness of the tattoo is consider to signify the extent of the good luck. In other words, the darker the henna tattoo, the better your luck will be.  So the theory goes. 
  • Most henna tattoos are put on the hands and feet.  This is because the skin here tends to be thicker, so it will absorb more of the henna, and the resulting tattoo looks darker than it would elsewhere.  
  • Back of the hand and top of the feet works best because it's easier to keep from disturbing the henna paste as it dries and interrupting the process by which the paste stains your skin.  But people do put henna tattoos in lots of places--palms, shoulders, calves, bellies, etc.

This henna tattoo starts on the fingers, descends down the palm, and onto the wrist. You can see how the tattoo is darker on the fingers and palm than it is on the wrist. This is because the skin on the wrist is thinner and doesn't take up the stain as well as on the hand.
(Photo from Ohio Body Art)

What It's Made of

  • Most henna artists mix the powder into a paste. Typical ingredients include:
    • henna powder
    • black tea or coffee
    • lemon juice or lime juice or orange juice or vinegar (mild citric or acetic acid)
    • sometimes the lemon juice etc. is mixed with sugar
  • That's it. People say the resulting paste feels like toothpaste.  In my very limited experience, the paste that was put on me felt smoother even than toothpaste. More like gel toothpaste.
  • The henna plant is not toxic, and neither are any of those above ingredients. (The situation is a little different for "black" henna, but I'll get to that in a bit.)
  • The paste is applied to your skin, usually through a tiny little tube, sort of like a minuscule cake decorating tip.  There are no needles, nothing is injected into your skin, it is not a painful experience at all. In fact, it's rather soothing. 

This applicator is like what my henna tattoo artist used.  Most of the applicator is a slender metal cone which tapers to a fine point with a hole in the end. At the top end of the applicator is essentially a plastic bag containing the henna paste. The artist squeezes the bag which makes the paste come out the tiny little hole at the bottom. The artist moves the applicator while squeezing out the paste. Often the artist makes very detailed designs and fine lines. I was pretty impressed with the delicacy of the skill.
(Photo from ehow)

This is another type of henna applicator. Here, instead of a little plastic bag, the receptacle that holds the paste is a plastic bottle.  The tip of the bottle is the very fine tube with a tiny hole at the end through which the henna paste emerges as it is squeezed out and applied to the skin.
(Photo from Wikimedia Commons)

  • Since nothing is injected into your skin, some people say it's technically not a tattoo. 
  • The stain sinks down into only the first few layers of your skin, all of which are dead skin cells.  As these skin cells are naturally worn away, so also will the henna tattoo. That's why it only lasts a couple of weeks. 

The Application Process

  • The paste goes on black.  You leave it on, allowing the paste to dry and so the stain has time to sink into your skin.

Henna paste being applied. Here you can see how it sits on top of the skin.
(Photo from White Ink Tattoo Center)

  • You'll want to let the paste dry for anywhere from 4-8 hours. The range of time depends on the mixture your artist is using, how hot & humid the weather is, if you've got lotion on your hands (or wherever the tattoo was applied), etc.
  • This means you won't want to wet your hand--or foot or wherever you got the tattoo--during that drying time. So this is why people tend to get their henna tattoo on their non-dominant hand. 
  • You'll also want to avoid brushing it against things, which will rub the paste off, or flexing and moving that part of your body very much. 
  • When the paste dries, it will flake off in bits.  Some of those bits got on my sheets and left faint brown stains. I washed my sheets right away and the stain came out, no problem.
  • After the dried paste flakes away, the brown stain on your skin will become visible.  Over the next day or two, the brown stain will continue to darken somewhat.
  • You'll still want to avoid washing the area that's been tattooed for about 24 hours.  After that, you can wash your hand, but you'll want to avoid any vigorous scrubbing.  The more scrubbing, the more of those dead skin cells you'll wash away, and the faster your tattoo will fade.

Process of a henna tattoo, from paste to no-paste to additional darkening.
(Image from New World Henna)

This is what the paste looks like as it's drying & flaking off -- kind of crusty.
(Photo from Cuded)

Some of the designs can be really elaborate.
(Photo from White Ink Tattoos Center)

Or even more elaborate. This person would have to keep from moving both of her hands for several hours in order for this tattoo to turn out properly.
(Photo from ehow)

Henna on feet & toes -- also very detailed.
(Photo from Lovetoknow Tattoos)

Some pregnant women get henna tattoos on their bellies--I suppose in hopes of giving good luck to their forthcoming babies.
(Photo from Pop Sugar)

This might be a cool idea for someone going through chemo.
(Photo from Best Tattoo Designs Ideas)

Black Henna

  • In most photos of henna tattoos online, the henna looks black. I'm going to assume that this is probably because the picture was taken right after the henna was applied, before the paste dried.
  • However, there is a thing people call black henna.  This type of henna leaves behind a much darker, blacker stain after the paste dries and flakes off.  
  • The ingredient that gets added to the henna that turns it black is a chemical called paraphenylenediamine, or p-phenylenediamine, or PPD.
  • PPD is a type of coal tar that's been used for many years in hair dye, especially for brunette & black dyes. 
  • Some people are allergic to PPD.  If you are allergic to PPD, you do not want this stuff to touch your skin. It is possible to develop an allergy to PPD after having been exposed to it over time. This is why the hair dye people want you to do a skin test before each self-dyeing session, to make sure you haven't developed a PPD allergy.
  • But since henna is used to dye hair as well as skin, people thought, why not add the PPD that we've been using in hair dye to the henna, to make it darker?
  • It turns out, this isn't such a hot idea because for those people who are allergic to PPD, they experience some pretty unpleasant results with the black henna tattoos.

You can see that this woman from Kuwait got a really beautiful henna tattoo. Except the henna that was used had PPD in it, and she turned out to be allergic to PPD. So her skin turned red and swelled up every place the black henna was applied.
(Photo from Evans et al., New England Journal of Medicine

  • Since it takes quite a few hours for the henna to soak into the skin, it can also take that long before people discover they are allergic to the PPD in black henna. So, often the artist using black henna does not know if one of his or her clients has had a bad reaction to the black henna.
  • The best thing to do, therefore, is to ask your henna artist if he or she uses black henna.  If you know you're allergic to PPD, ask if he or she would use the regular henna instead. 
  • If you get a black henna tattoo and then discover you're allergic because your hand is tingling and itching and swelling up like a beautifully decorated basketball, go to your doctor as soon as possible. Most likely, your doctor will prescribe some sort of steroid that will take down the swelling.
  • If the reaction and the swelling are severe, you could wind up with permanent pigmentation -- your temporary black henna tattoo would become permanent.
  • Even if you think you're not allergic to PPD, it's probably best to avoid the black henna.

Now I'll show you some more pictures of regular henna tattoos because there are a lot of really magnificent ones.

(Photo from Factortruth

(Photo from Henna Tattoo Body Art)

Foot henna
(Photo from Cuded)

Leg henna
(Photo from Cuded)

Some henna tattoo artists are also adding additional dyes to make the henna different colors.
(Photo from Tattoos Time)

I think this one wins the prize. This is a wedding henna tattoo, complete with all sorts of colors, glitter, and body art gems.
(Photo from Crafty Nitti)

Desdemona's Designs Ohio Body Art, FAQ
Henna Arts, Frequently Asked Questions
The Henna Page, Why doesn't henna stain last forever like a tattoo?
Henna Mehndi, How to Mix Henna? FAQs
FDA Consumer Information, Temporary Tattoos May Put You at Risk
Colby C. Evans, and John D. Fleming, Allergic Contact Dermatitis from a Henna Tattoo, The New England Journal of Medicine, 2008; 359:627