Friday, June 21, 2013

Science Clock Series: Part II

In part two of this series, we look at a subject from nuclear physics. Or chemistry. It's kind of at the point where the two overlap.

Today's number is two, and it is approximately equal to:

\[2\approx\text{T}_{1/2}\,^{237}\text{Np}\,(\times10^6\,\text{y})\] T\(_{1/2}\) refers to the half-life of a substance, which means the amount of time, on average, that it takes for half of a sample of a radioactive substance to decay into something else. \(^{237}\)Np is the chemical symbol for the element neptunium (specifically, the isotope neptunium-237), and “\(\times10^6\)” is scientific notation for “multiply this number by 1,000,000”. So the whole expression means “approximately equal to the half-life of neptunium-237 when multiplied by two million years,” referring to two.

Neptunium is the element with atomic number 93 and the first transuranic element. This means it is the first element after uranium (atomic number 92), and is thus only found in nature in extremely tiny amounts (after uranium no element is found in nature in anything other than trace amounts). Neptunium has at least nineteen known isotopes, of which the most stable is neptunium-237 (also written \(^{237}\)Np) with 93 protons, 144 neutrons, and a half-life of 2.144 million years.

So the full expression can be read as “two (million years) is approximately equal to the half-life of neptunium-237.” And now you know where it comes from. Check back next time for something from cosmology! Click here to jump directly to it.

As an aside, the name neptunium comes from the planet Neptune which follows the planet Uranus out from the Sun, just as neptunium follows uranium in the periodic table. (Plutonium also follows neptunium just as Pluto follows Neptune [most of the time, anyway].) Uranium was named after the seventh planet from the Sun, which is now known as Uranus, but which was not always the case. When it (the planet) was originally discovered there was some controversy over what it should called: Herschel, the discoverer, wanted “Georgium Sidus” (“George's Star” in Latin), after his patron King George III of England. Astronomers from other countries were (understandably) a bit miffed at a celestial object bearing the name of a foreign monarch, and several alternate names were proposed, including "Uranus" by the German astronomer Johann Bode, who first determined Uranus' orbit. A few years later when Bode's colleague Martin Klaproth discovered a new metal (in 1789) he named it uranium in support of Bode's proposed name (which eventually beat the competition to become the standard today). By the time neptunium was discovered (officially in 1940) the name Uranus was long the standard, so neptunium and later plutonium were simply nice additions. 

Wednesday, June 19, 2013

Science Clock Series: Part I

For Christmas my parents got me a novelty clock with scientific references for the numbers which I put up in my office. It's a nice clock, although this was the best picture I could get of it:


Now, since there are a lot of different scientific references on this clock I decided to write a mini-series on them, each post focusing on one of the numbers. Although I'm familiar with nearly all of them there are a few that I myself need to look up, so it'll be a learning experience for me as well. I'll be explaining as many of the scientific concepts that come up as I can for those who aren't familiar with them.

Today I'm going to start with number one:

\[\rho\ \text{of}\ \text{H}_2\text{O}\ (\text{g/cm}^3\ \text{at}\ 4^\circ\text{C})\] The Greek lower-case letter \(\rho\) (rho) is traditionally used to represent density in chemistry; H\(_2\)O is water, made up of two hydrogen atoms and one oxygen atom. The g/cm\(^3\) notation means grams per cubic centimeter, so the whole expression means “the density of water in grams per cubic centimeter at four degrees Celsius,” which refers to one.

Why it equals one is rather interesting. Fundamentally it equals one by definition; water is such an important and ubiquitous substance (it makes up 65-70% of the human body, covers 70% of the Earth's surface, etc.) that it was chosen such that the mass of one cubic centimeter of water was equal to one gram (or equivalently one gram of water occupies one cubic centimeter), so that the density of water is exactly one by definition. Thus, you can immediately tell if a substance is more or less dense than water at a glance by seeing whether its density is greater or less than one. If a substance's density is less than water it will float in water; if greater, it will sink. Sodium, for example, has a density of 0.968 g/cm\(^3\), or 96.8% that of water, meaning that sodium will just float on water. (Or at least, it would if it wasn't reacting so incredibly fast with water to produce hydrogen and igniting it in powerful explosions.) Magnesium, with an atomic number merely one higher than sodium, has a density of 1.738 g/cm\(^3\), 70.38% more dense than water, so magnesium would sink in water.

However, there's a wrinkle with this whole scenario that the critically-minded among you may have been wondering about: it turns out that the density of a substance varies with temperature. For most substances, the density decreases as the substance gets hotter, and increases as it gets colder. The reason for this is that greater temperature means greater average energy on the molecular level, which translates into higher average molecular speed, which tends to lead to increased molecular spacing and thus the same amount of mass taking a slightly larger area. Typically the changes in density are fairly small for liquids and solids, larger for gases.

As I mentioned, most substances increase in density as the temperature decreases, and this is mostly true for water; however, it has a slight hiccup as it approaches its freezing point. Rather than decreasing monotonically as the temperature decreases to 0\(^\circ\)C, the density of water reaches a minimum at 4\(^\circ\)C, then begins to increase slightly as it approaches its freezing point.

This behavior is unusual, thought not entirely unique; there are a few other substances that display similar quirks. However, in water's case, this little quirk is quite important for life on Earth. Because of this quirk, ice floats on liquid water, which is highly unusual (most solid substances sink in their liquid forms). Ice is a pretty good insulator, so ice forming on the surface of lakes helps keep the water beneath it from freezing more, leaving liquid regions underneath throughout the winter where fish and other creatures can survive. And when spring comes, the ice floats on the surface of the water where it can be melted by the Sun, rather than sitting out of reach on the bottom of lakes and rivers.

This quirk of density is but one of the many ways water is a very unique substance (one reason it was chosen to define density), but that isn't the focus of this post which is already getting a bit long. Next time we'll take a look at something from nuclear physics! Click here to jump directly to it.

Wednesday, June 12, 2013

Cuttting-Edge Astronomy on Mauna Kea: Visiting JCMT and UKIRT

Well, this post is a few weeks late, but I thought I'd put up some pictures from the trip I took on Memorial Day. Along with a few co-workers (current and previous), I got to take a tour of both the James Clerk Maxwell Telescope (which I work for) and the United Kingdom Infrared Telescope, both of which are currently part of the Joint Astronomy Center (although that will change in the months to come, though exactly how is not yet known).

Anyway, I'd never been inside UKIRT before this, and only once inside JCMT (as I posted about a month or two ago). That time wasn't for sightseeing, so I got to see a lot more of the telescope this time. You might remember from that post that I got a picture of the telescope from behind, like this:

The main JCMT dish, lit from beneath.
The weather that day turned out to be absolutely miserable (very cold, fine, blowing rain the entire day), dashing our hopes to hike to lake Waiau and the summit, so we instead took a nice leisurely tour of both telescopes. The last time I was there I didn't climb up high enough to see into the dish, but I was able to do so this time, and get a nice picture:

The JCMT primary dish.

Here's another picture at a slightly different angle, showing the secondary mirror support structure and the grand arch of the overhanging Gore-Tex covering:


If these pictures disorient you as they do me, it may help to remember that the telescope was parked at this time, and the dish is pointing straight up. The metal panels you see in the background are part of the wall. The Gore-Tex is arching over the dish, and provides it protection during operation. (Yes, it's left in place. It's nearly transparent at sub-millimeter wavelengths, so the telescope basically looks right through it.)

Speaking of the Gore-Tex membrane, part of our tour took us near where its upper edge rested (just off to the right in the photo above). It was nicely backlit, and I was inspired to have a friend take some pictures of me with it:

Can't talk now, I'm posing!
Deep in thought.

A different angle that shows more of the upper edge of the membrane.
After getting that dramatic posing out of my system, we took a walk outside around the upper catwalk, just below the roof. This turned out to be a much worse idea than it seemed, because the door we came out from was mostly sheltered from the wind; as we curved our way along the narrow metal catwalk, jutting out from the building a couple stories above the ground and completely exposed to the elements, we faced more into the wind at every turn which made it nearly impossible to actually see or appreciate anything due to the cold mist being blown in our eyes. It was still a neat experience, and I hope to be able to do it again sometime when I can properly appreciate it.

Anyway, after some more looking around we headed up from Sub-millimeter Valley to the ridge where UKIRT is located. The contrast between the two buildings is quite striking, and very interesting (I wish it had been clear enough to get pictures of them from the outside). You see, JCMT is built such that the entire upper portion is one with the telescope, and it all rotates together (yes, the operator room too). This gives it (the building, at any rate) a feeling of lightness, or even unsubstantiability, because except for the first floor everything is built to be light and able to move. UKIRT, however, is built more traditionally, with the building firmly anchored and only the telescope itself able to move, which gives it (again, the building) a feeling of rock-solid permanence and durability. Anyway, here's a picture of the telescope itself:


The secondary mirror is on the left, and the long black tube is where the light goes after it reflects off the secondary down through the hole in the center of the primary. The orange-colored part is the harness that controls it motion east and west across the sky. Here's a view from another angle, with the secondary visible on the right:


And from up above, looking down towards the main mirror, which is covered up by the dust covers:

The “W” and “S” stand for west and south; this picture faces north.
Now, I titled this post “Cutting-Edge Astronomy” but I haven't really talked about it. Since it's getting late I'll keep this short, but basically, neither of these telescopes “see” in optical light, the sole domain of telescopes for over three hundred years (UKIRT is infrared, JCMT is sub-millimeter). Being able to take pictures of objects in infrared and the longer sub-millimeter wavelengths is something that probably couldn't have been even conceived of as recently as a hundred years ago, and only within the last fifty has it become possible at all. It is only within that time that we have been able to see the universe in more than the infinitesimal fraction of the electromagnetic spectrum that out eyes are sensitive too. If you consider all the information that visible light brings to us about the universe, there are countless times that amount of information out there in other wavelengths just waiting to be discovered by us.

And it's not just that JCMT and UKIRT are pioneering new regimes. There are, after all, two other sub-millimeter telescopes, one dedicated infrared, and at least two more telescopes capable of infrared observing on Mauna Kea. JCMT and UKIRT also have some of the most advanced, state-of-the-art detectors on them, such as SCUBA-2 that I work with, which is the world's best sub-millimeter “camera” currently. (I'm not as familiar with UKIRT, but I know it also has some amazing detectors. In fact, last year, UKIRT was the world's number one most productive telescope in terms of papers published.)

Anyway, it's getting late as I said so I'm going to wrap this post up here. A hui hou!

Wednesday, June 5, 2013

Earthquakes

One thing that you never have to worry about while living on the flanks of some of the most active volcanoes on Earth is boredom. Case in point: today we had an earthquake (I'm fine, by the way).

Although there have been hundreds of small earthquakes in the few years I've been here, most of them down by Kīlauea area, I can only say I've felt two with any certitude. Today's magnitude 5.2-shaker, however, despite having an epicenter located 57 miles away and 10 miles deep in the crust, produced definite, unmistakable effects here in Hilo.

I was sitting at my desk after lunch, doing a little coding when a sudden jolt struck the building at about 2:14 PM. It was short and sharp, to the point that I almost wondered if I hadn't imagined it. A few seconds later however an aftershock arrived that dramatically shook the entire office building for about five seconds before dying away. If it had gone on any longer I was beginning to contemplate evacuation, but we haven't had any more aftershocks as of the writing of this post.

I lived through a few large earthquakes during my childhood in Taiwan, but it's been over thirteen years since then and in that time I've felt only a few minor earthquakes. I'd forgotten the what it's like when the Earth - that solid underpinning of your whole life that you ordinarily never give a second thought to - begins to move uncontrollably under your feet. For a minor earthquake, it can be fun; you get a little shake, but there's no damage done. For a large earthquake it's terrifying. Thankfully this one was still small enough that I doubt there was much serious damage done, although the shear pins in UKIRT broke (as they're designed to do to protect the telescope from earthquakes) which will probably be take a bit to fix.

The earthquake was probably related to the youngest member of the Hawaiian island chain, a submarine volcano located off the south-east coast of Hawai'i island named Lōʻihi.

Monday, June 3, 2013

More Creepy-Crawlies of Hawai‘i

So about fifteen minutes ago I was sitting at my computer, trying to come up with a post idea that wouldn't have me up till all hours past my bedtime writing it, when I noticed a cockroach in my room. This was rather disturbing, both because I've never seen a cockroach in my (new upstairs) room before, and because from as far as I can remember I've had a near crippling irrational phobia of cockroaches, along with spiders and centipedes.

Of course, since I've already encountered both of those here already (and both in my hair, what's up with that?), I suppose it was only a matter of time till the trifecta of creepy-crawlies was complete.

This time, however, the thought flashed through my head that I had but a little over two weeks previously attained the lofty and grown-up age of four-and-twenty years, and it came to me that I could slink away, try to deal with it like I always had by simply trying to avoid it, or that I could exercise the higher-thinking areas of my brain, deal with the situation rationally, and overcome my phobia. I resolved to grasp the bull by the horns, or the cockroach with the hands, which come to the same thing in the end, really.

Let me be perfectly clear: when I said phobia, I meant it. Just seeing a cockroach is A Big Deal for me, causing an immediate spike in anxiety levels, pulse rate, breathing, and circulating blood adrenaline, and a strong urge to put enough distance between me and it that I don't need to worry about it any more. I can't remember any specific incident that caused this response; I just can't remember ever not having it.

So anyway, despite fighting off a minor panic attack, I decided to overcome the irrational terror and simply grab the thing and dispose of it. I still couldn't bring myself to just grab it (the thing was probably less scared of me than I was of it), but I chanced upon some discarded plastic wrapping which was just enough prop – barely – to shore up my rapidly-waning courage to the point where I was able to make a few ineffectual swipes at it before finally encompassing it in my hand.

That moment, when I had it, helpless, in hand; it was...perhaps “liberating” would be a good word. Those of you without phobias (you lucky people) might not be able to appreciate what a deep personal triumph overcoming one is, but I'm sure all the rest of my readers can relate, in some manner. In all honesty I love cockroaches' overall design-shape (so sleek and smooth) and I like looking at them safely contained behind glass, though that didn't stop me from offing this particular intruder; trespassers of that sort cannot be tolerated!

Anyway, if this post seems somewhat less lucid than is my wont, it might have something to do with the not-inconsiderable levels of stress hormones still making their way out of my bloodstream. But until next time, a hui hou!