What I Learned Today

My class on the History of Books and Libraries started off with a tour of ancient writing systems and libraries. We covered a wealth of fascinating content. For example, it had never occurred to me that the Lascaux cave paintings were three-dimensional, since they were painted onto irregular cave walls! I’d only ever seen flat-looking 2D pictures like the one at right. Today you can visit the Lascaux cave paintings in 3D through the magic of the Internet. Do it! I sat there enthralled as I floated through the twisty little passages and came away with an entirely different sense of this early artwork. “Early” is an understatement. The paintings are estimated to be 17,000 years old!

I also learned that cuneiform tables had a 3D aspect not only in their wedge-shaped impressions but because, as chunks of clay, they were rather thick, and scribes took advantage of this to write on all sides, including the edges. Browse all sides of real tablets yourself! (Now I want to make my own, maybe out of Play-doh.)

We discussed various writing systems, and you can browse several historical scripts as well as (quite curiously) constructed scripts, mainly for English, that replace our current alphabet. One of my favorites is Heptal (rendered at right). We also discussed boustrophedon, a word I will never again misspell.

Finally, we covered the ancient libraries at Nippur, Ur, Nineveh, and Alexandria. The library at Nineveh was the creation of Ashurbanipal and grew to contain 30,000 clay tablets, with a complex indexing system and integrated book curses. My assignment for this week was to create a “learning activity” about Ashurbanipal and his library.

Dare you take my quiz? Will you earn yourself Ashurbanipal’s admiration or his scorn?

Adventure 2 in “Adventures with a Microscope” is titled “We Become Crystal Gazers.” The author continues:

We are not going to peer into such crystals as fortune tellers use, in which they claim to be able to predict that some rich relative is going to leave you money, or some equally nonsensical bosh.

No indeed, this is about chemistry. So I followed along, heated some water, and mixed up supersaturated solutions of various interesting substances from my kitchen. And wow, check it out! (Click to enlarge.)

Salt. Best viewed ~1 hour after deposition on the slide, with partial crystal formation; if you wait longer, the slide becomes crowded, and since the crystals are cubes, it’s hard to get them all in focus (too much relief!). I love this shot. It reminds me of Flatland.

More salt, the next day, with larger crystals.

Baking soda, which apparently creates sparry crystals.

Sugar! This one took a full day to form interesting crystals. But wow, they are gorgeous!

More sugar, almost a butterfly-like configuration. I expect the symmetry is coincidence.

The biggest surprise for me — my saliva, 24 hours later, had created these awesome fractal patterns. At first I thought it might be nucleation following tiny scratches in the slide glass, but the fact that they’re fractal renders this unlikely. No clue what this is, but my best guess is that it’s just random diffusion patterns, like these manganese fractal patterns.

Aha, I found an article titled “Dendritic growth in viscous solutions containing organic molecules” which has these great examples:


Caption: “Crystal patterns of some body fluids: (a) saliva; (b) cerebrospinal fluid; (c) urine; (d) blood serum.”

My examples seem to match the “blood serum” image the best, but I assure you it was saliva. Not sure what’s going on in their sample (a)!

The more I panned across the expanse of fractal growth, the more it started looking like a map of a European city. Is it not marvelous?

The world just expanded by a factor of ten. At least.

Of course this is true in a literal sense, given the arrival of my Celestron 44345 microscope. I can now see down to scales previously invisible to my eye, magnifying at 40x, 100x, 200x, 1600x! But even more meaningful is the figurative way in which things have expanded. I have access to a rich, teeming layer of reality that previously existed only in a hypothetical fashion. And because this is a microscope with a digital camera embedded in it, I can also store and share what I see.

I first took a look at the seven prepared slides that came with the microscope. Here are some examples of the fantastic sights I saw (click to zoom):

Pine:

Epithelium:

“Apple” (seed? cell? blossom? wha?):

I’ve now placed an order for a set of blanks so that I can prepare my own slides to study anything I encounter — and even just within the confines of my house there is a veritable zoo of things to study. High on my list is sampling from the cornucopia of interesting structures that grow in my compost bin. I can’t wait to share what I discover!

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!