What I Learned Today

The summer and winter solstices happen around the 20th of June and December, respectively. Around the 20th? That seems rather… imprecise, for an astronomical event with a precise definition: the time at which the Sun reaches its “highest or lowest excursion relative to the celestial equator on the celestial sphere” or, for the viewer standing on the Earth, its highest or lowest altitude from the horizon. This is determined by the Earth’s orbit and corresponds to the time at which your current hemisphere’s pole points most closely to, or farthest from, the Sun. So why doesn’t it happen at the same time each year?

Inspired by an awesome book I recently acquired (“Engaging in Astronomical Inquiry” by Slater, Slater, and Lyons), I decided to investigate. I used the Heavens Above site to pull up historical data for the summer and winter solstices going back to 1980. I plotted the time for each solstice (in Pacific time) as its offset from some nearby day (June 20 or December 21). And sure enough, here’s what you get:

The solstice time gets later by about 6 hours each year, until a leap year, when it resets back by 24 – 6 = 18 hours.

Of course, the solstice isn’t really changing. The apparent change is caused by the mismatch between our calendar, which is counted in days (rotations of the Earth), and our orbit, which is counted in revolutions around the Sun. If each rotation took 1/365th of a revolution, we’d be fine, and no leap years would be needed. But since we’re actually about 6 hours short, every 4 years we need to catch up by a full rotation (day).

Now, we all know about leap years and leap days. But this is the first time I’ve seen it exhibited in this way.

Further, you can also see a gradual downward trend, which is due to the fact that it isn’t *exactly* 6 hours off each year. It’s a little less than that: 5 hours, 48 minutes, and 46 seconds. So a full day’s correction every four years is a little too much. That’s why, typically, every 100 years we fail to add a leap day (e.g., 1700, 1800, 1900). 11.25 minutes per year * 100 years = 1125 minutes, and there are 1440 minutes in a day. But that’s not a perfect match either… which is why every 400 years, we DO have a leap day anyway, as we did in the year 2000.

This is what, in computer science, we call a hack.

And now it is evident why for every other planet, we measure local planet time in terms of solar longitude (or L_s). This is the fraction of the planet’s orbit around the Sun, and it varies from 0^o to 360^o. It’s not dependent on how quickly the planet rotates. It’s still useful to know how long a planet’s day is, but this way you don’t have to go through awkward gyrations if the year is not an integral multiple of the day.

By the way, you can get a free PDF version of ‘Engaging in Astronomical Inquiry’. If you try it out, I’d love to hear what you think!

We’ve heard many discoveries over the past decade of planets around other stars. Today astronomers announced the detection of seven new comets around other stars. You can read more here: “Exocomets may be as common as exoplanets”.

Why should we care? Well, comets are a lot smaller than planets, so it’s impressive that they can be detected at all. Even more impressive, these discoveries were made with a 2.1-m telescope on the ground, not in space. You might be wondering how exactly they were detected if it’s so hard even to find Earth-sized planets. That’s because these comets aren’t being detected directly, e.g., by the brief drop in stellar brightness when a planet transits in front of it. Instead, what’s actually being detected are slight perturbations (lasting about 5 days) to the star’s spectrum across multiple wavelengths, which indicates a compositional difference. Since we don’t expect the star to briefly change its composition and then revert back, this is interpreted as seeing gases boiling off the comet as it passes close to the sun.

If so, I’d expect that the particular changes would serve as a kind of “fingerprint” for that particular comet, and be somewhat repeatable the next time it approaches its star. But comet periods can be a lot longer than planet periods (at least in our solar system) so it might take a while to get any repeat signals.

The scientific reason this is interesting is that it can serve to fill in a gap in our knowledge. We’ve seen systems with dusty disks surrounding the star (before planets form), and we’ve seen more mature systems with their planets already formed. We haven’t yet explored the in-between stage in which a lot of material (comets, asteroids) is moving around in the process of forming into large planetesimals. For that reason, astronomers targeted young (type A) stars for the exocomet hunt.

Further, turns out that the technique used wouldn’t work with older/cooler stars. In discoverer Barry Welsh’s talk today at the AAS meeting (he’s giving a press conference tomorrow), he noted that the spectral absorption features they think come from comet outgassing get “narrower and harder to detect in older stars.” I’m not sure of the specifics on this, but it suggests we won’t be able to find exocomets in all of the stars we’ve been studying… at least this way. Astronomers’ innovations will continue to push the envelope!

While at the American Geophysical Union meeting this week, I got to attend a lecture by Ira Flatow (host of NPR’s Science Friday). In his talk, “Science is sexy,” he argued that the image of science has changed from that of the scruffy-haired, wrinkled professor to a younger, fresher, more attractive one. As evidence, he cited the “Mohawk guy,” Mythbusters, and several movies and Broadway shows that have employed a scientific theme or concept. Popularizing science is one thing, but sexualizing it is another. He offered a smorgasbord of other examples that ranged from amusing (the Big Bang Theory, or “what would happen if Friends were physicists”) to offensive (“It’s a Girl Thing” video) to delightfully clever (“The Longest Time” video on divergent evolution).

Ira also cited a paper called “The 95% Solution” which he reported as saying that Americans get only 5% of their knowledge about science from formal education (school). The rest of it, he said, comes from libraries, field trips, aquariums, the Internet, TV, and of course radio shows like Science Friday, which oddly he did not cite. :) But this rather surprising 5% claim turns out not to be quite what the original paper says. The authors note that the average person spends only 5% *of their lifespan* in a classroom. (I am not the average person.) The article encourages directing more resources to these other, non-classroom settings since they in theory have the chance to educate the population in “the other 95%.”

I liked their depiction of the U.S. as having a “vibrant free-choice science learning landscape” — i.e., we enjoy a wealth of opportunities for learning about science. But the article’s deeper argument is a little more radical. If only 5% of one’s lifetime is spent in school, it argues, then the current “school-first” approach of trying to get more and better qualified science teachers in classrooms is not only misdirected, but it doesn’t work. The article notes that although U.S. schoolchildren lag behind their international peers in science literacy, U.S. adults outperform their counterparts (but the article cited no data source, and a web search I conducted suggested that this comes from a study showing that a whopping 28% of U.S. adults have basic science literacy, not exactly a stellar performance, and only barely edging out other countries). Since “only 30% of U.S. adults have ever taken even one college-level science course,” the authors conclude that U.S. adults have been learning science from all of these other sources, not from school.

It’s great that people can learn new things from the world around them, and from informative displays and exhibits that have been set up. But it’s not really surprising; humans are natural scientists and experimenters, as anyone knows who’s watched a toddler for more than two minutes. Is it really the case that teaching science in schools is doomed to failure? Could we not continue working on curriculum innovations instead of giving up and heading to the Science Center IMAX? If the latter, why drag students through school in the first place?

Ira’s other big message was the need for effective science communication. He illustrated this point with one of my favorite examples, a video of Grace Hopper explaining what a nanosecond is to David Letterman (apparently CBS has yanked all copies of this video clip — very sad!).

He also noted that Neil deGrasse Tyson will host a new Cosmos show starting next year (woo hoo!).

Okay. Science is sexy.

This is the coolest LaTeX doodad I’ve found in ages. Detexify is a brilliant combination of useful UI and machine learning. When you can’t remember what the latex command is to render a particular symbol, you simply DRAW it and Detexify gives you a ranked list of matches. You can then give it feedback about which one was what you wanted, which it uses to re-train its model and improve for the future.

I found this tool while trying to hunt down the LaTeX command for §, which I’d never used. Here’s what I drew:

Notice it has the correct command at the top of the list!

I love discovering new ways that machine learning can be used to make daily life easier. Well, in this case for those who use LaTeX on a daily basis. That’s everyone, right?

The question is ill-formed, since Watson never existed outside of Sir Arthur Conan Doyle’s pages, which clearly indicate that he was a man. And yet… and yet… this tongue-in-cheek analysis of Watson’s gender is so delightfully entertaining that who cares whether the question makes sense? Read on. Read the case to support the claim that Watson was a woman.

P.S. I learned from this talk that there are a total of 60 Sherlock stories. What! I must have missed some of them. Time to go a-hunting.