What I Learned Today

A friend offered this great tidbit of information:

The navigation lights on the airplane wings are red on the left side and green on the right side, so that people on the ground and in the air can tell at a glance at night which direction the plane is heading.

It turns out that ships do this, too, and it not only permits the determination of direction but also the resolution of right-of-way questions. From wikipedia:

If he sees green, he is to the impinging craft’s starboard and has the right of way. If the pilot sees the red light, he knows that the approaching craft has the right-of-way, and he is required to deviate from his course to avoid the collision.

So the next time you’re near an airport at night, look up and see if you can detect both colors in approaching or departing planes (you’ll then be able to tell which is which).

Thanks, Leighton! (And thanks to Jim for his addenda, in the comments.)

Today I tried something new by attending the Southern California Games Day, a board game extravaganza held every 2-3 months. I wasn’t sure exactly what to expect, or who would be there, but I ended up staying for seven hours and playing three new games. I learned to play:

• Glory to Rome! : A role-based building game like Puerto Rico in which you attempt to rebuild Rome.
• St. Petersburg : A phase-based building game with little connection to Russia, as far as I could tell.
• Leonardo da Vinci : A building game in which the goal is to be the first to build Leonardo’s inventions!

These were all fun, although the last game stretched out because no one at my table had played it before and we had to work through the rules before we could play. However, I’d picked that game — with a name/thesis like that, how could I resist? I came in 3rd, 4th, and 2nd in these games — 4th in St. Petersburg despite being in the lead for the majority of the game! The victory point multipliers at the end snatched the lead away from me and awarded it to my opponents. I would have come in first in the Leonardo game if I hadn’t mistakenly read one of the resources needed to build one particular invention. (My single complaint about that game is that the cards are somewhat hard to read.)

All in all, it was a fun day with lots of new people, rules, strategies, and gotchas.

As part of a NASA proposal I am writing, I need to be able to combine multiple .pdf files into a single, larger .pdf file. Sure, you can do this with Acrobat — but you have to pay for it. Today I was delighted to learn about pdftk, the PDF toolkit from AccessPDF. You can download the program here, although I instead got it via fink on my Mac, so your mileage may vary.

At any rate, this gem of a program runs on the command line with simple, easy-to-use syntax. For example, to concatenate f1.pdf and f2.pdf, you type

pdftk f1.pdf f2.pdf cat output combinedfile.pdf

But wait, there’s more! You can pick and choose which pages you want, e.g.

pdftk A=f1.pdf B=f2.pdf cat A1-3 B2-4 A6 output combinedfile.pdf

to get the first three pages from f1.pdf, then pages 2-4 from f2.pdf, then page 6 from f1.pdf… neatly organized in the order you specify! And these are just some of the “simple examples”. There’s more power here than I’ll probably ever need in terms of PDF manipulation. Thank you, Sid Stewart.

Postscript: although this program works like a charm for small files, it dies an ugly death on large ones. The best alternative I was able to find for the Mac is Combine PDFs, which handles large files just fine. However, it is a graphical app. This is handy, since you can drag-and-drop PDF files into it and assemble them manually, but it is also difficult to automate. pdftk is a command-line app, so it’s easy to incorporate it into a Makefile to automatically refresh your output .pdf file if any of the components change; Combine PDFs has to be run manually each time. Still, it was able to give me what I needed for the proposal. Thanks, MonkeyBread Software.

I received a great book, “What Einstein Told His Cook 2”, for Christmas. (I’d previously read, and enjoyed, the first book.) This is a book about food and cooking, written by a chemistry professor. I hardly need say more about why it’s an engaging read, but I will anyway. I would much rather approach cooking from the science side, where there are rules and reasons and determinism, than from the art side, where there is chaos and personal taste and approximation. These books explain the whys and hows behind common kitchen practices, very sensibly, very educationally.

Therefore, I ended up finding the section on alcohol and various drinks to be enthralling, even though I don’t drink and expected it to be pretty much irrelevant. One tidbit I took away from the chapter was an explanation for why beer always comes in (opaque) cans or dark brown bottles:

Hops are an essential ingredient in beer, and not only for the aroma and bitterness. They clarify the beer by precipitating the proteins in the wort, and they have antibiotic properties that help preserve the beer. Among the more than 150 chemical compounds that have been identified in their essential oil are chemicals (terpenes) called isohumulomes, which are light-sensitive. When struck by either visible or ultra-violet light, they break down into very active free radicals that react with sulfur in beer’s proteins to produce smelly compounds called skunky thiols, which the human senses of taste and smell are able to detect at levels of a few parts per trillion. […] Beer that has been exposed to light for as little as 20 minutes reputedly can develop a “skunky” taste. That’s why beer is packaged either in cans or in light-proof brown bottles.

It had never occurred to me to wonder why beer doesn’t come in clear plastic or glass bottles, like soda. Now I know!

Today I learned how to do an extra-loose bindoff for a scarf I’m knitting. I’d rate myself as an “intermediate” knitter — willing to try new techniques, patterns, and stitches, but still needing some good instructions (or a knowledgable friend) to venture into the unknown.

The scarf I’m knitting is a Moebius Scarf. That is, like a Moebius strip, it has only one side (achieved with an ingenious twist in the circular needle setup — kudos to Cat Bordhi and her book, “Magical Knitting”!). Interestingly, for the purposes of knitting (but also obviously, if you were to think it through), a Moebius strip also has only one edge. So you knit around and around and that makes the scarf grow outwards, on both sides, from the center. It’s great fun, in terms of knitting and topology.

At any rate, once this scarf comes off the needles, you want it to have a lot of flex, so that it can drape fetchingly around your neck, rather than bunching up along the edges due to a too-tight bindoff. Binding off too tightly is a common affliction, so that many knitting books recommend using a larger needle once you get to this final step; but who really has a second set of somewhat-larger needles ready for every project they attempt?

Magical Knitting recommends the following solution:

Knit 2, * insert left needle through the front of 2 stitches on the right needle, knit 1 (dropping both stitches off), knit 1. Repeat from *.

Lovely!