Yesterday was the equinox, but I couldn't help noticing that sunrise was at 7:07AM and sunset was at 7:16PM. That stretches the definition of "equi" a bit. Looking ahead, the day won't be within a minute of 12 hours until September 25 or 26. (One's a minute longer, one's a minute shorter.) So off to Google I went.

There are two things going on, it turns out. The first is that the equinox is relative to the center of the sun, but we count sunrise and sunset from when the top is visible. But that only accounts for 2.5-3 minutes at my latitude.

The bigger factor is atmospheric refraction: after the sun has actually set (all parts past the horizon), or the reverse in the morning, you can still see the sun. What? Yeah, apparently you can look westward at sunset and see "the sun" even though the sun is not in your line of sight; light bends. This effect varies with atmospheric conditions, but is usually good for about six extra minutes of day.

I said that I won't see a 12-hour day here for a few more days. Apparently that effect gets stronger as you move toward the equator; this site says at 5 degrees North that date isn't until October 17. It also says the day is never exactly 12 hours at the equator, when I thought the equator was the one place where you had reliable 12-hour days all year. Today I learned.

I wonder -- because I'm the sort of person who wonders about stuff like this -- what the effect is in halacha, Jewish law. The day starts at sunset, but when beginning Shabbat we add some extra time just to be safe -- 18 minutes in most communities. That's l'hatchila, what you should do from the outset, but b'dieved, after the fact, if you cut into the 18 minutes with your preparations, it's ok because it's not actually sunset yet. Except... maybe it is? If you have a bad week and light candles two minutes before (nominal) sunset -- when you can still see the sun in the sky, except it's not there -- have you kindled fire on Shabbat? Or do you go by what you can see anyway? I plan to ask this on Mi Yodeya if it's not already there, but first I have to finish Sukkot preparations.

Update: asked.

Unless you're on the equator, neither the earliest sunset nor the latest sunrise of the year is on the winter equinox (source). In Pittsburgh, the earliest sunset is usually around December 9 or 10. People who keep Shabbat tend to notice this.

This happens because apparent solar time doesn't line up exactly with mean solar time. The day isn't consistently (or exactly) 24 hours long, and "noon" usually isn't exactly 12:00. Plus there's some shift because of latitude. Fine.

I wondered why there wasn't a corresponding effect at the summer solstice, and played around with this slider to map it out. There actually is an effect, but it's much smaller -- the earliest sunrise was parked at the same time (rounded to the minute) from June 10-19, and the latest sunset is parked at the same time from June 23 - July 1. So in the week or so surrounding the solstice there's barely any change, while in December the boundaries more more visibly. The latest sunset is June 23 which is barely past the solstice, but it's also July 1 (and every day in between of course). And the earliest sunrise is only a couple days before, but also a week before. So what I notice is "earliest sunrise June 19, latest sunset June 23", even though those bands are wider. In the winter, on the other hand, sunset has been creeping later for a week and a half when you get to the solstice.

I guess this, too, is because of latitude, but it's still not intuitive to me. I wonder what's still wrong with my mental modeling.

siderea

The Arctic Light from TSO Photography on Vimeo.

thnidu posted a link to this video composed of time-lapse photography covering one day in Helsinki -- two views, side by side, one at each solstice:

(Link later broken, alas.)

The husband of a member of the Debatable Choir posted video from our Pennsic performance.

I didn't know enough chemistry to fully parse this geeky comic by ohiblather, but I still laughed out loud when I saw it.

xiphias reports research that seems to be begging for an IgNobel award. As he points out, it's worthy because first it makes you laugh and then it makes you think. I mean, what publishable conclusion would you expect from researchers doing an MRI on a dead salmon?

I feel fortunate that "talk like a pirate day" fell on Rosh Hashana, meaning I was shielded from most of the antics. But I enjoyed top ten halachic problems for a Jewish pirate, forwarded by dglenn. Should I be worried that I have defensible answers for several of them?

Fun website mash-ups from metahacker and others. From one of the comments: "OKAmazon: People who had sex with this person also liked..."

Signal boost: kyleri makes hand creams, lip balms, soaps, and similar items, and she is currently having a sale. I bought some of her creams at Pennsic and am happy with the results.

I haven't turned off the spelling checker in Firefox on this machine yet because I do sometimes make typos that it catches, but this post almost made me do so. :-)

A few days ago, I was reflecting on Challenger and had started to compose an entry in my head. But this past week was a little hectic and I never got the words down in bits. Now, instead, I will write a slightly different entry.

I am old enough to remember the first landing on the moon, but I wasn't old enough at the time to understand what the big deal was. (I was 5 going on 6.) My formative years, educationally-speaking, fell during that decade or so when the space program was no longer "current events" but was not yet "history". Neither my parents nor my small circle of friends followed the space program, so I was pretty unaware until, probably, sometime in college. I heard a lot of space history for the first time from the filk tape "Minus Ten and Counting", which prompted me to go out and learn more. Now that I think about it, I have never properly thanked Julia Ecklar and Leslie Fish for that.

I remember the morning of Challenger quite clearly. I knew there was a launch coming up, but had lost track of the schedule. And I wasn't so hard-core that I watched (or listened to) launches live anyway. I caught them on the news when I could, or read about them in the paper. I was at work that morning, and I had a cubicle, not an office, so I wouldn't have had the radio on anyway.

Scott walked out of his office into my cubicle and said "It blew up". I thought he was talking about some code I had handed over to him. I said "on what? I ran the test suite". And he said no, not that, and I should come into his office and listen to the radio. And I did.

I didn't actually see the footage until later that night. They were playing it over and over, and I sat there stunned. And several of us said that this was probably the end of the manned space program, even though these had hardly been the first deaths. They were the first deaths that we had witnessed, as opposed to reading about, though, and it made an impact.

That was 17 years ago, and it didn't kill the space program, though clearly that program hasn't been a major priority. But it's been there, and that's important to me. I have hopes that some day people will actually leave this planet for more than a few days or weeks or months. I desperately hope that we do a better custodial job on the next planet we get our hands on, too.

Shuttle trips have become fairly routine. There have been enough that I guess I got complacent about it, the way I do about driving a car. I didn't even realize that today was the day they were coming back.

Today was Shabbat. I didn't hear the news. Tonight I read my email and saw a message from someone in the local SF club saying something like "shall we plan a memorial after this week's meeting?". Memorial? What the heck was he talking about. I figured maybe some SF author had died. I bopped over to CNN to see if I could tease it out.

Damn. How did that happen? My heart goes out to the victims. Seven, like before. A first, like before -- last time a teacher, this time an Israeli.

I feel mildly guilty that my heart aches a little bit more for those seven (and their families) than it does for many of the truly innocent, unexpected deaths that happen around the world every day -- earthquakes, famines, wars, disease. Astronauts, at least, know they're going into danger; they're taking a chance. The folks who die in brushfires or monsoons or tornados, or in skyscrapers in New York, weren't doing anything risky or out of the ordinary. I should have more sympathy for them than for astronauts. But I don't, somehow, though I am not uncaring. Call it a character flaw, I guess.

I suspect that this is a setback, not an end, to the space program. But I do wonder how many setbacks it can withstand before an impatient public calls to shut it down and spend the money elsewhere. I wonder if private enterprise will be positioned to take up the slack any time soon.

[1] Literally, "praised is the true judge" -- said upon hearing of someone's death. Meaning: God had His reasons, even if we can't comprehend them.