I was recently interviewed by Dale Basler and Brian Bartel from Lab Out Loud, a podcast for the National Science Teachers Association, and it’s now online. I was a member of NSTA for several years back when I was doing education workshops at Sonoma State University. They do great work for teachers across the country, equipping them with the science they need to educate students, so I was really happy to do the interview.

We talked about eggs and the equinox, my first and second books, and spent most of our time talking about the need for skepticism, especially in the classroom. I suggest going to their site and taking a look around, or you can download the interview MP3 directly.

Turns out they had a warmup interview with someone else as a prelude, an apertif if you will, for mine, too. Think of it as a calamari appetizer.

I like the scifi blog io9, I really do. I read it every day, and I get a huge kick out of it (though avoiding the Doctor Who spoilers is tough).

But they had a post recently that kinda, well, blew it epically.

The topic was bad physics in movies. You might think that my calling them out on this is just due to insane jealousy on my part because they’re getting to be a popular blog and they didn’t link to my movie reviews even though I was among the first (if not the first, thankyavurrymuch) to review the science in movies on the web, and of course being an honest man I cannot necessarily dismiss that. Happily, though, my ego has the ability to charge on undeterred.

The io9 folks decided to rate several popular movies on how they treated various topics in physics, like faster-than-light (FTL) travel, communicating with aliens, sound in space, and so on. They did it like a check list, so if a movie abused a given topic, it got a check in that column.

Problem is, they got a whole lot of things wrong in their checklist! For example they only fault the Star Wars movies and The Last Starfighter for having FTL, when nearly every movie on their list has it.

So here is a more complete dissection of their list. Think of it as a check on the io9 checklist, sorted by movie:

1) 2001: They correctly said it didn’t have sounds in space, which is good, but then said it had a "weird depiction of exposure to vacuum". Weird? It was actually pretty accurate, and it’s rare to this day to have a movie treat this topic even close to correctly.

io9 than gave 2001 a check mark in the "people move in slow motion in zero gravity" category. I would say that’s a tough call; people in the movie move carefully in microgravity (a better term for it, though a lot of folks still use "zero-g"), not necessarily slowly. You don’t go zipping around in microgravity, you have to move a bit slowly to make sure you don’t launch yourself across the cabin.

Finally, they don’t rate 2001 as having FTL, but it does! In the end, when Dave Bowman takes The Ultimate Trip, he’s flying through the galaxy using wormholes or some such thing.

2) Contact: They don’t give it a check mark for FTL, when again that was in the movie. Actually, that was the whole purpose of The Machine, and was the whole point of the ending of the movie when Ellie has to present her science as if it were faith.

3) Armageddon: I am no fan of this movie (which is like saying black holes suck a little, or a supernova is a slightly energetic event), but io9 gave it a check under "Nearby asteroids aren’t drawn close by gravity". I was scratching my head over what that meant, but then saw a helpful description at the bottom of their post:

Asteroids or other objects shouldn’t be able to float close together without falling into each other’s gravity.

Well, that just raises further questions (for you Futurama geeks out there)! I’m not sure precisely what they mean by that, but gravity doesn’t works like a crane, reaching out and grabbing stuff and instantly moving it around. Also, and it pains me greatly to say it, as I recall Armageddon doesn’t mention the Earth’s gravity affecting the orbit of the asteroid; but just because they don’t mention it specifically in the script doesn’t mean you can give them a demerit.

4) Deep Impact: Once again, we get a check mark in that asteroid category. The only thing I can figure out for this in the movie is that the two chunks of the comet drift apart, and don’t fall back together. But the movie had it right! The two chunks separate after the detonation of a nuclear weapon under the surface of the original comet. Each of the two pieces of the comet are far too small to have enough gravity to pull significantly on the other. So they essentially orbit the Sun freely.

Did I miss something here? Any ideas from my BABloggees? I’d ask io9 in a comment but my account there doesn’t allowed me to leave comments.

5) Mission to Mars: They forget to note that there was FTL at the end of the movie; Gary Sinise’s character uses it to go to the alien homeworld. I would also give the movie a half-check under "Easy communication with aliens" topic, too.

6) Serenity: They give this one check marks under "All planets have Earth gravity" and "All planets have one climate world-wide". There is a narration at the beginning of the movie that specifically discusses terraforming, so you can’t fault the movie that. While we don’t have the tech now to terraform a planet, we know in principle it can be done. Firefly and Serenity both establish they have artificial gravity, though I suppose you can legitimately call them on that since there isn’t anything in well-established physics today that would allow that (though it’s impossible to say what will happen in the next few hundred years).

7) Stargate: io9 gave them no check for FTL. Um, what’s the title of this movie again?

8) "Alien" franchise: They give it a demerit for having interbreeding between aliens and humans. But that’s not really what was happening; humans were hosts, not contributing any DNA. Update: See the comments below the post; I concede that in the last two movies there was a limited form of interbreeding, kinda sorta. It was clear in the movies that the aliens were incredibly tough, resilient, and flexible for different environments. It’s not too much to ask that humans could be walking (well, sleeping) incubators for them. Also, the movies had FTL, which again went unchecked.

9) Enemy Mine: io9 didn’t have it checked under FTL.

10) They gave Apollo 13 a clean bill of health, which is true enough (though you’ll note the astronauts do in fact move slowly in microgravity), but the movie did have other (mostly trivial) accuracy errors, mostly due to combining different things from different Apollo missions for the sake of storytelling, which I’ll forgive (especially since it’s such an awesome movie).

11) They also gave The Right Stuff a clean bill of health, which is fine. My nitpick isn’t with the movie so much as with the book; the author made the astronauts look like posers, and the test pilots the real heroes. I object to that because it’s hugely unfair to the astronauts; both parties played their parts in history, and both showed incredible aptitude, bravery, and intelligence.

So there you go. As I learned long ago, nitpicking the science in movies is fun, and makes for a great blog entry, but in my opinion the io9 author in this case missed a lot of stuff, and was arbitrary about others.

I may have missed a few examples, too. The only movie on their list I’ve never seen is Solaris, so there might be something there too (I never saw Alien 4 either, having learned the franchise was dead and buried with Alien 3, but I assume there’s nothing there that wasn’t in the first three).

The hard part with all this, I’ve learned, is to know when a little snark is deserved and when it isn’t. I make mistakes too, even in my own areas of expertise, and sometimes I deserve a little teasing and sometimes it’s just an honest mistake. I don’t mean to be mean to io9, and had they made a few mistakes I wouldn’t bother commenting. I think the article would have been vastly improved with some details; specific examples from the movies to elucidate their points. They obviously spent a lot of time researching this (read: watching lots of movies), so that extra step wouldn’t have been too hard.

Again, I still love io9 and I won’t slow down drinking from their firehose of scifidom. There are lots of scifi blogs on the web, and even with this stumble io9 is among the best I’ve read.

I know I haven’t been posting much lately; it’s been an interesting week. I’ve had several projects keeping me busy, including one cool one that I’ll be telling y’all about later. I also have some old friends visiting, so we’ve been out and about, and I get home too tired to write anything.

We went hiking in the Flatirons yesterday; they are a series of huge blocks of sedimentary rock that were uplifted off an inland seabed when the Rockies pushed their way up through the crust 300 million years ago. They’re the icons of Boulder, really, and fantastically beautiful. There’s a park at the base, and we had a great time walking around and playing in the small patches of snow leftover from some unusually warm days last week.

As I was walking along a trail, I noticed this piece of bark that had peeled off a Ponderosa pine. How could I not take a picture of it?

Pareidolia follows me everywhere. I guess that’s the point of it.

Warning: Doctor Who intensive material follows. Spoilers for "Blink", too.

So as a reward to myself for finishing up a pile of work, I watched the Doctor Who episode "Blink." This is the second time I have seen it, and it was even better this time. Honestly, even if you are not a Who fan, this one episode stands out. I’d put it up against any other single episode of any show, including "Out of Gas" in Firefly.

Anyway, I think I have found an inconsistency, and it’s making me insane. What follows are spoilers, so if you’ve seen it, help me out. If you haven’t, then get it! Watch it! Love it!

So the detective shows Sally the cars and the TARDIS parked in the police station. He says they’ve had it a while, it’s their crown jewel of the collection. What must have happened is that after the Doctor and Martha are sent back to 1969 by the angels, the police found the box at the house and moved it.

But then later, maybe that evening, Sally and Larry are at the abandoned house, and she finds the TARDIS in the basement!

I can’t see how that’s anything but a mistake. I even tried to think of some way for the Doctor to have taken the TARDIS to that house after all the events we see (he knows she was in the house when he "talks" to her — best conversation scene ever written, ever, by the way), but it’s a stretch, and I don’t think this is how it was meant to have happened…

Sally sends the TARDIS in the house back to 1969, rescuing the Doctor and Martha (but not the detective! That seems cruel). Then he takes it back to the house and leaves it there for her to find — maybe he shows up just an hour before she and Larry come to the house. Then the Doctor and Martha walk to the police station, grab the TARDIS sitting there, and off they go!

That actually works. However, it means the TARDIS is in two places at the same time, and it may be that the TARDIS in the basement is in some sort of causal loop. Also, and I have to stress this, he leaves the detective in 1969. He has to, I know, but yikes.

So, does this make sense?

Still, what a story! This is up there with The Terminator for sheer time travel wonderfulness, and of course, wibbley-wobbley timey-wimeyness.

Warning: this post has math in it. A lot. Some of it might even be correct. If you are mathophobic, then you might want to skip to the end, where I reveal what Rosebud means.

And for those of you who are incredibly anal, yes, I know I kinda lost track of significant digits about 2/3 of the way through this. I was using a calculator, and just used whatever numbers it gave me to the last decimal place, leaving off for the most part trailing 0s. Sue me. I’m free on February 29th, 4800.

When I was a kid, I had a friend whose birthday was on February 29th. I used to rib him that he was only 3 years old, and he would visibly restrain himself from punching me. Evidently he heard that joke a lot.

Of course, he was really 12. But since February 29th is a leap day, it only comes once every four years.

And why is it only a quadrennial event?

Duh. Astronomy!

We have two basic units of time: the day and the year. Of all the everyday measurements we use, these are the only two based on concrete physical events: the time it takes for the Earth to spin once on its axis, and the time it takes to go around the Sun. Every other unit of time we use (second, hour, week, month) is rather arbitrary. Convenient, but they are not based on independent, non-arbitrary events.

It takes roughly 365 days for the Earth to orbit the Sun once. If it were exactly 365 days, we’d be all set! Our calendars would be the same every year, and there’d be no worries.

But that’s not the way things are. There are not an exactly even number of days in a year; there are about 365.25 days in a year. That means every year, our calendar is off by about a quarter of a day, an extra 6 or so hours just sitting there, left over. After four years, then, the yearly calendar is off by roughly one day:

4 years at 365 (calendar) days/year = 1460 days, but

4 years at 365.25 (physical) days/year = 1461 days.

So after four years the calendar is behind by a day. That means to balance it out again we add that day back in once every four years. February is the shortest month (due to some Caesarian shenanigans), so we stick the day there, call it February 29th, the Leap Day, and everyone is happy.

Except…

The year is not exactly 365.25 days long. Our official day is 86,400 seconds long. I won’t go into details on the length of the year itself (you can read a wee bit about it here), but the year we now use is called a Tropical Year and it is 365.242190419 days long. With malice aforethought — my calculator won’t hold that many digits — let’s round it to 365.2421904.

So it’s a bit short of 365.25. That hardly matters, right?

Actually, it does, over time. Even that little bit adds up. After four years, we don’t have 1461 physical days, we have

4 years at 365.2421904 (real) days/year = 1460.968762 days.

That means that when we add a whole day in every four years, we’re adding too much! We should really only add 0.968762 days. But that’s a bit of a pain, so we add in a whole day.

So even though we add a Leap Day in to balance the calendar, it’s still a bit off. It’s a lot better, for sure, but it’s still just a hair out of whack. This time, it’s ahead (since we added a whole day which is too much) by

1 – .968762 days = 0.031238 days, or about 45 minutes.

That’s not a big deal, but you can see that eventually we’ll run into trouble again. The calendar gains 45 minutes every 4 four years. After we’ve had 32 leap years (128 years of calendar time) we’ll be off by a day again!

So we need to adjust our calendar again. But 128 years is hard to remember, so it was decided to round that down to 100 years. After a century, we’ll have added that extra 45 minutes in 25 times (every four years for 100 years = 25 leap years). To be precise, after 100 years the calendar will be off by

25 x 0.031238 days = 0.780950 days.

That’s close enough to a whole day.

Confused yet? Here’s another way to think about. After 100 years, we’ll have had 25 leap years, and 75 non leap years. That’s a total of

(25 leap years x 366 days/leap year) + (75 years x 365 days/year) = 36,525 calendar days.

But in reality we’ve had 100 years of 365.2421904 days, or 36524.2421904 days. So now we’re off by

36,525 – 36524.21904 = .78096

which, within roundoff error, is the number I got above. Woohoo.

So after 100 years, the calendar has gained almost a whole day on the physical number of days in a year. That means we have to stop the calendar and let the spin of the Earth catch up. To do this, every 100 years we don’t add in a leap day! To make it simpler, we only do this in years divisible by 100. So 1700, 1800, and 1900 were not leap years, we didn’t add an extra day, and the calendar edged that much closer to matching reality.

But notice, he says chuckling evilly, that I didn’t mention the year 2000. Why not?

Because even this latest step isn’t quite enough. Remember, after 100 years, the calendar still isn’t off by a whole number. It’s ahead by 0.78095 days. So when we subtract a day by not having leap year every century, we’re overcompensating; we’re subtracting too much. We’re behind now, by

1 – 0.780950 days = 0.21905 days.

Arg! So every 100 years, the calendar lags behind by 0.21905 days. If you’re ahead of me here (and really, I can barely keep up with myself at this point), you might say "Hey! That number, if multiplied by 5, is very close to a whole day! So we should put the leap day back in every 500 years, and then the calendar will be very close to being right on the money!"

What can I say? My readers are very smart, and you’re exactly correct. So, of course, that’s not how we do things.

Instead, we add the leap day back in every 400 years! Why? Because if there is a stupid way to do something, that’s how it will be done.

After 400 years, we’ve messed up the calendar by 0.21905 days four times (once every 100 years for 400 years), and so after four centuries the calendar is behind by

4 x 0.21905 days = 0.8762 days

and that’s close enough to a whole day. So every 400 years February 29th magically appears on the calendar, and once again the calendar is marginally closer to being accurate.

As a check, let me do the math a second way, in the same method I did for the leap century gambit above. In 400 years we’ve had 303 non-leap years, and 97 leap years. The total number of days is therefore

(97 leap years x 366 days/leap year) + (303 years x 365 days/year) = 146,097 calendar days.

But we’ve really had

400 x 365.2421904 days = 146096.8762

We can see the remainder is 0.8762 days, which checks with the previous calculation, and so I’m confident I’ve done this right. (phew)

Of course, the calendar’s still not completely accurate at this point, because now we’re ahead again. We’ve added a day, when we should have added only 0.8762 days, so we’re ahead now by

1 – 0.8762 days = 0.1238 days.

Funny thing is, no one worries about that. There is no official rule for leap days with cycles bigger than 400 years. I think this is extremely ironic, because the amount we are off every 400 years is almost exactly 1/8th of a day! So after 3200 years, we’ve had 8 of those 400 year cycles, so we’re ahead by

8 x 0.1238 days = 0.9904 days.

If we then left leap day off the calendars again every 3200 years, we’d only be behind by 0.0096 days! That’s phenomenally accurate. I can’t believe we stopped at 400 years.

But despite that, we’re done! We can now, finally, see how the Leap Year Rule works:

What to do to figure out if it’s a leap year or not:

We add a leap day every 4 years, except for every 100 years, except for every 400 years. In other words…

If the year is divisible by 4, then it’s a leap year, UNLESS

it’s also divisible by 100, then it’s not a leap year, UNLESS FURTHER

the year is divisible by 400, then it is a leap year.

So 1996 was a leap year (The Little Astronomer was almost born on leap day that year, in fact). 1997, 1998, and 1999 were not. 2000 was a leap year, because even though it is divisible by 100 it’s also divisible by 400.

1700, 1800, and 1900 were not leap years, but 2000 was. 2100 won’t be, nor 2200, nor 2300. But 2400 will be.

This whole 400-year thingy was started in the year 1582 by Pope Gregory XIII. That’s close enough to the year 1600 (which was a leap year!), so in my book, the year 4800 should not be a leap year.

But who listens to me? If you’ve gotten this far without blowing out your cerebrum, then I guess you listen to me. All this is fun, in my opinion, and if you have gotten this far you know as much about leap years as I do.

Which is probably too much. All you really need to know is that this year is a leap year, and we’ll have plenty more for some time. You can go through my math and check me if you’d like…

Or you can just believe me. Call it a leap of faith.

The live chat is happening RIGHT NOW! The chat’s over now. Nothing to see here, folks. Move along.

Here is the embedded stream. But if you go to UStream.tv you can join the chat room.

The last live chat was a lot of fun, and even though I’m still fooling around with the setup I figured I’d do another one. This time, I’m thinking 00:00 UT Sunday/Monday February 24/25 (today as most of you read this, no doubt).

So that’s 19:00 Eastern (US) time, if that helps any, or 5:00 p.m. my (Mountain) time. To make it easier, here is a countdown timer:

I’ll put up another blog post closer to the time of the chat with an embedded stream from my camera and all that. Stay tuned!