David D. LevineScience Fiction Author

Okay, this time I really will be brief. We have to make an early start tomorrow.

We started off the day with a talk by Ruben Gamboa on computing in astronomy. Modern astronomy is all about computers — the days of staring through eyepieces and developing film in darkrooms are over. Computers are used for controlling equipment, automating repetitive tasks, organizing data, and building scientific models. Computers are very good at boring tasks like looking for comets and supernovas, so most comets these days are named after discoverers like NEAT (Near-Earth Astronomical Telescope) rather than Hamner-Brown. The next generation of survey telescopes will generate 30TB of data per night (that’s half a Library of Congress or 1/20 of YouTube). Google is working with LSST to build a system to manage all this data. And scientific models (usually systems of partial differential equations) are now being used more and more with brute-force computational techniques rather than by being solved in the conventional way (many useful models can’t easily be solved). In the future, scientific models will be computer programs rather than systems of equations.

Jerry Oltion then gave a loose, interactive talk on humans in space and astronomy in fiction. A few tidbits:

• The human body does not explode in vacuum. One NASA volunteer was exposed to hard vacuum in a space suit test accident; he passed out after 14 seconds (his last conscious memory was of the water beginning to boil on his tongue) but they restored normal atmospheric pressure quickly and he survived just fine.
• Space capsules and space stations tend to stink badly, and this is a serious problem.
• Air in free fall does not convect, which means that everything that heats up has to be cooled by fans; the space shuttle is LOUD inside.
• Sex in space has almost certainly happened, but Jerry thinks that the reason nobody has talked about it is that it’s not all that good. In space your nose stuffs up, you smell, perspiration doesn’t evaporate, your blood pressure goes down, and experiments on the Vomit Comit have shown that even hanging onto each other and achieving penetration is a hassle.
• Stan Schmidt warns writers that it is extremly unlikely to have a habitable planet around a star with a name. (Named stars are all bright, and the bright stars tend to be too hot or too large for Earth-like life.)
• There is an “extra” day in the sidereal year (vs. the solar year) because the Earth rotates once per year due to its orbit around the sun, in addition to its daily rotation. For every 365 times the sun rises, the stars rise 366 times.
• If the moon is visible in the West, the tide is going out (generally speaking). Similarly, if it’s visible in the East, the tide is coming in.

Mike Brotherton’s grad student Rajib Gauguly then gave a talk on quasar absorption lines (“studying gas you can’t see using light that isn’t there”) which was highly technical, but after six days of this we had the background to understand it. Mostly. I’m not going to try to summarize it here.

We finished up with a brief talk on the search for exoplanets (there are 228 known exoplanets around nearby stars, some as small as 5 times the mass of the Earth), an open Q/A period, evaluations, and logistics for getting everyone home. We all went out to Laramie’s only Thai restaurant for dinner, then went back to the dorm and packed.

All done. Whew. What a week. I learned a lot, hung out with some great people, and ate way too much.

We head off to Denver for the Worldcon bright and early tomorrow. My program schedule:

• Wed 11:30: Launch Pad: Astronomy for Writers
• Wed 16:00: Reading: David Levine
• Thur 10:00: Short Fiction: On its way out or a way to break into the market?
• Thur 14:30: Have blogs and listservs replaced fanzines?
• Fri 10:00: Clarion West Writers Workshop: How it Helped My Career
• Fri 13:00: Signing (45 minutes)
• Fri 14:30: Kaffeeklatch
• Sat 11:30: Clarion West Student Readings, the 21st Century

I’d greatly appreciate it if you’d show up for my reading and Kaffeeklatch. I can promise fun conversation and silly noises.

Woke up early enough today for breakfast in the dining hall (which is only open 7-8am, what were they thinking?) and conversation with about half the gang. The downside is that I got less sleep than usual and am now tired and headachey, so this entry will be shorter than yesterday’s (if I know what’s good for me).

Mike Brotherton started off with a lecture about galaxies and cosmology. Almost everything we can see with the naked eye at night is in our own Milky Way galaxy (this is, apparently, its actual name — I expected it to have an official scientific name like Galaxy Number One or something, but no). One exception is the Andromeda galaxy, which is barely visible as a hazy star near Casseiopeia.

Herschel tried to determine the shape of the galaxy (1785) but didn’t do very well because so much of it is obscured by interstellar dust and gas. The galactic plane, in fact, is well above the bright line we can see, but obscured by dust. We can use wavelengths that are not obscured by dust (e.g. infrared) and “standard candles” such as Cepheid variable stars, whose absolute brightness can be determined from their periods, to determine the galaxy’s actual shape.

Stars in the galactic disk have nearly circular orbits, while “halo” stars outside the disk have highly elliptical orbits. The orbits of stars in our galaxy and others show that most of the mass of the galaxy is distributed smoothly throughout the galaxy rather than concentrated in the center. The speeds of the orbits tell us that there is a LOT more of this mass than we can account for through visible objects such as stars. But what is it?

Could this dark matter be ordinary dust and gas? No. We know the abundancies of baryons (protons and neutrons) in the universe from studying the Big Bang, and there aren’t nearly enough to account for the invisible mass.

Could it be WIMPs (Weakly Interacting Massive Particles) such as neutrinos? No. Although neutrinos don’t affect normal matter much, they do affect it, and we have performed experiments (using large quantities of dry cleaning fluid) that show there aren’t enough of them either. A theoretical WIMP called the “axion” has been proposed but never observed.

Could it be MaCHOs (Massive Compact Halo Objects) such as black holes and brown dwarfs? Maybe, but probably not. We can detect these objects through “gravitational lensing” (a distant object changing its brightness or apparent position as a MACHO passing in front of it warps its light) and we don’t see enough such events to account for the missing mass.

Could it be that we are simply wrong about gravity? No. MoND (Modified Newtonian Dynamics) seemed plausible until 2006. The Bullet Cluster consists of two clusters of galaxies that have recently passed through each other. We can see the hot gas of these two clusters (which is normal matter) using X-ray telescopes, but we can also find their centers of mass using gravitational lensing of the galaxies behind the cluster. The two centers of mass are farther apart than the visible gas. This tells us that the majority of the mass in the two clusters does not interact with itself or with the matter of the clusters in the same way as normal matter. (This Scientific American article includes a very helpful video simulation.)

I must say that I was both confused and skeptical about the very weird stuff called “dark matter.” (Note: not to be confused with “dark energy,” which we talked about later.) I didn’t understand why this strange non-interacting stuff had to be invoked when it could just be, well, matter that was just dark. But the Bullet Cluster was for me, you should pardon the expression, the smoking gun.

Many galaxies have spiral arms. If you look at a picture of a spiral galaxy it looks just like water going down the drain, or a hurricane, and you think you can tell which way it is rotating. The actual rotational direction is the other way. Spiral arms are, in fact, standing waves in the interstellar medium. At the leading edge of these waves (the inside edge of each sickle-shaped arm), new stars are born as the interstellar medium impacts the shockwave. The bigger, hotter stars burn out first, so the leading edge is brightest, fading away to blackness as most of the newborn stars burn out or fade away.

We can measure the distance to other galaxies by using Cepheid variables and type Ia supernovas (these are white dwarfs in binary systems that collapse when they accrete too much matter from their companion — we know exactly how bright they are because they explode immediately when their mass rises to a certain value). These “standard candles” tell us that distant galaxies are moving away from us with a speed proportional to their distance.

The galaxies aren’t moving through space, as any fule kno… it’s space that’s expanding. This expansion is happening everywhere, but it’s only visible in intergalactic space because at smaller scales the force of gravity is greater than the expansive force. This is why the galaxies are getting farther apart instead of just bigger.

By studying the three degree Kelvin background radiation that is the echo of the Big Bang, we can determine the initial conditions of the universe and determine that the total mass of the universe is almost exactly what is needed to make the universe “flat”, meaning that it will neither expand forever nor contract in a Big Crunch: the expansion will slow down and stop at some point. But there isn’t enough matter, even including dark matter, to account for this flatness, and when we measured the rate of deceleration, we got a surprise: it wasn’t slowing down at all, it was speeding up!

Turns out there’s a “cosmological constant” in Einstein’s equations, which was thought to be zero, but if we set it to a negative value it explains both the accelerating expansion of the universe and the missing mass. The missing mass is the mass equivalent of this weird anti-gravitic energy. We don’t know what this “dark energy” is — it has never been observed directly — but it makes the equations balance.

It may be that the cosmological constant itself is increasing. If it stays the same, the universe expands so fast that all other galaxies will eventually fade from view. If it is increasing, it will eventually get big enough to overcome atomic forces and everything in the universe will be torn apart: the “big rip.” For now, though, it’s less powerful than gravity and other forces, meaning its effect is only visible at the very largest scales.

After that cheery reassurance we went to the computer imaging lab where we got a talk by Chip Kobulnicky on imaging in astronomy. Raw images from the Wide-Field Planetary Camera on the Hubble space telescope look awful. They consist of four rectangles (three large, one small) with big visible seams between them, speckles of noise, and cosmic ray streaks. Scientists and technicians have to do a lot of processing to make them look all pretty and colorful. We also got some hands-on experience using a program called ds9 to combine the R, G, and B images of the Ring Nebula that were taken at WIRO on our field trip the other day into a single color image. Here’s the result:

(It’s kind of grainy because the exposure was short.)

The day ended with a talk on SETI by scientist/philosopher Jeffrey Lockwood. This talk was a bit of a surprise as we spent the whole time talking and writing about what messages we, as writers, would send to aliens, ignoring questions of transmission mechanism and language. It was an interesting writing exercise, and thought-provoking, but was so different from the hard science focus of the rest of the week that some of us felt kind of whiplashed.

One of the things I wrote during this session was a message to express the importance of “pattern” to humans while simultaneously encoding the Fibonacci sequence:

Instance.
Instance.
Another instance.
It happens again.
Why does it happen again?
Can we predict what the next instance is?
By observing phenomena, we learn about the universe and learn to predict events.
We find patterns and recurrences in all kinds of physical phenomena, from molecules to stars, simple to complex, insert and alive.
Once we have discovered a pattern, we can build devices, craft new experiments, build more knowledge on top of what we have already learned, and even begin to make changes and improve our environment.

We finished the evening on the roof of the physics building, looking at binary stars, globular clusters, the planet Jupiter, and various satellites (including the International Space Station) with night-vision goggles, binoculars, and two very nice amateur telescopes.

Apparently I do not know what’s good for me. Night, all!

Very busy. Having much fun. I keep forgetting keen stuff and encourage you to read other attendees’ blogs for the full Launch Pad experience (and photos).

Yesterday started off with a talk by Jerry Oltion about amateur astronomy. In the astronomy world, “amateur” is not a pejorative. Many pro astronomers are also amateurs, and many significant discoveries have been made by amateurs. Even if you have an 80″ scope at your day job, you might want to have a smaller scope in your garage because you can use it whenever you want and point it wherever you want.

Cheap telescopes often brag about how much they magnify, but the important thing for astronomy is not to make the image bigger but to make it brighter, so as to see objects too dim for the naked eye. For this reason, size counts, but the diameter is more important than the length (ahem). One danger of amateur astronomy is “aperture fever” — the desire for a bigger and bigger scope. It used to be that you had to grind your own mirrors, but machine-made mirrors are now good enough that hand-grinding is no longer necessary (though it’s still a rite of passage). You can now buy one-meter mirrors for a not unreasonable amount of money.

Telescope mounts include Dobsonian (tilt and swivel, like a cannon), equatorial (also tilt and swivel, but with one axis aligned with the North Star, making it easier to follow an object as the Earth rotates), and Jerry’s own “trackball” mount (a sphere mounted on rollers). You can get computerized scopes with GPS, once you’ve aligned them you can just key in a desired object and they swing right to it, but the affordable ones tend to be cheaply made and the set-up time may cost you as much time as you save in finding each target — also, you lose the learning opportunity and the fun of the hunt.

Why do bright stars appear to have four points? This is due to diffraction effects from the “spider” that supports the secondary mirror, which usually has four supports.

Mike Brotherton then gave a high-speed, high-density lecture on “everything you always wanted to know about stars.”

People have been studying stars for a long time and there are many “palimpsests” of earlier ideas. For example, information about stars used to be presented in charts in color order, from blue to red. Now that we know that blue stars are hot and red stars are cool, the X axis of these charts now represents temperature rather than color, but they’re still shown with the blue (hot) end on the left, so the temperature increases from right to left! And the reason the spectral classes are the order OBAFGKM (Only Bad Astronomers Forget Generally Known Mnemonics) is because the original spectral classes were in order of strength of the hydrogen line in their spectrum (A = strongest, O = weakest) but we now know that O stars are the hottest and M are the coolest. What happened to C, D, E, H, I, J, and L? They were duplicates and were dropped. But the letters are still used.

Stars can be graphed on the Hertzsprung-Russell diagram with spectral class (temperature) on the X axis and luminosity (total amount of light output) on the Y axis. Most stars fall in a roughly diagonal band from hot-and-bright (upper left) to cool-and-dim (lower right), which is called the Main Sequence. This is a tidy sequence of mass from about 18 solar masses at the top to 0.1 solar masses at the bottom. It is not a temporal sequence! Most stars spend most of their life moving slowly across the width of this band.

A star’s properties are uniquely determined by its mass and chemical composition. Bigger stars burn hotter and have shorter lives.

Stars are born in areas of dense gas and dust. Something, such as a shock wave from a supernova, causes an area of the gas to begin to condense. These protostars get hotter and brighter as they condense, but after a while their luminosity actually starts to go down, even as their temperature increases, because they are getting smaller. Shortly after fusion begins they blow off their surrounding coccoon of dust and gas and become visible; this transition is called the “birth line” on the H-R diagram, even though the star is really “born” when fusion begins. The star continues to condense and stabilize, throwing off jets of material which may in turn shock the interstellar medium into new protostars, until it eventually settles down on the main sequence at a point determined by its mass.

When a star reaches the end of its life, what happens depends on its mass. A typical star will move off the main sequence toward the upper right (becoming a giant star, which gives much more light than a main-sequence star of the same temperature because of its larger surface area), then blow off its outer envelope, leaving a white dwarf remnant in the lower left (hot but small, so not very luminous). A smaller star cools to a brown dwarf; a larger star explodes violently as a supernova.

After class we drove up to the Wyoming Infrared Observatory (WIRO), which despite its name is used only for optical observation these days. When we arrived the sky was overcast, but we toured the facility, which consists of a very ordinary-looking small house with a giant dome attached. Inside that dome was the telescope, a bus-sized spindly contraption with an eight-foot mirror on one end and a three-foot cubical box on the other. We gawked and took lots and lots of pictures. The moment when they cranked open the roof was just awesome.

Now we waited for the sun to set and hoped the clouds would clear. We ate our dinner, talked with the two grad students staffing the observatory, amused the cat (Nu Bootes, pronounced “new booties,” successor to the previous observatory cat Mu Bootes, pronounced “mew booties”), played cards and chess, and enjoyed the view. The view from the mountain was spectacular, looking like a Star Trek matte painting as the sun set. Just then it started to drizzle and they had to close the dome.

Oh well, I thought, at least we got to see the telescope. But right around the time we were getting ready to bail, the clouds parted. Huzzah!

We headed back into the dome to see the grad students charge up the instrument cluster with liquid nitrogen to reduce noise. Then we were shooed out, presumably to prevent being crushed as the giant machine turned in the pitch dark of the dome.

I spent the rest of the evening alternating between the control room, where I saw live pictures of the Ring Nebula on computer screens and asked lots of questions, and the gravel lot outside the dome, where the Milky Way came out and we gawked at the night sky. We had a pair of night-vision goggles, through which I saw a satellite and the Andromeda Galaxy.

Very, very cool. I got back to the dorm around 1am, which explains why I didn’t blog yesterday.

Today started out with a nice hike around Turtle Rock in Vedauwoo, which offered spectacular views), a little rock climbing, and pleasant temperatures, but took a lot longer than originally budgeted, throwing off the rest of the day’s schedule.

After lunch we met in the university’s small planetarium, which is rare in that it is still equipped with a traditional optical “starball” (AKA “planetarium projector” or “giant ant”). Modern digital projectors are more flexible, but there’s something about the smooth motion and ineffable “directness” of the old-fashioned starball that makes it a more engaging way of learning about the night sky. Unfortunately, optical starballs are difficult and expensive to maintain… many features of this one were not working. Our host Jim Verley gave a very entertaining talk about both the workings of the planetarium and about night sky basics.

Mike Brotherton then continued his talk about stars. More than half the stars in the galaxy are members of binary (or more) groups. Stellar evolution in binaries is complicated and depends on the two stars’ relative masses. For example, in a pair that consists of a big star and a small star, the big star will blow up into a giant star first, and its smaller companion will have the opportunity to pull away some of its outer atmosphere. If the smaller star pulls away enough mass, it may become the bigger member of the pair. Later, when it becomes a giant, the white dwarf remnant of its formerly-larger companion may pull away some of its mass in turn. In some cases the larger star may completely absorb the smaller, which can take as little as a couple of months.

If one member of the pair is a white dwarf, the matter coming into it from the other star is whipped into an accretion disk due to conservation of angular momentum. This infalling gas is incredibly hot, and may outshine the original star and emit large quantities of X-rays. Hydrogen may also settle on the surface of the white dwarf in sufficient mass to begin fusing. If this occurs, it ignites all over the star at once in a spectacular explosion: a nova. Because this only affects the surface of the star, it may happen again and again, even periodically.

Our sun will eventually (5 billion years) expand to a red giant about the size of Earth’s orbit. The Earth wll move out slightly, because the sun’s mass will have decreased by then, but it’s really an academic question whether it’s broiled by falling into the sun’s atmosphere or merely toasted by proximity. Either way it’ll be a mighty warm day. Eventually the outer parts of the sun’s atmosphere will be blown away (comparatively gently) and the core will settle down as a white dwarf.

Massive stars (25 solar masses or more) burn hydrogen at the core for about 7 million years, then helium for 500 thousand years, then carbon for 600 years, then oxygen for six months, then silicon for one day. At this point the star resembles an onion, with a silicon-burning core surrounded by an oxygen-burning layer surrounded by a carbon-burning layer, and so on. Silicon fuses to iron, but iron doesn’t fuse at all. When all the silicon is used up, the core collapses, beginning a reaction that destroys the star in a massive explosion: a supernova, which produces a flood of neutrinos and creates all kinds of heavy elements. Every atom in the universe that’s heavier than iron is the result of a supernova explosion. The remaining core becomes either a neutron star or a black hole, depending on its mass.

Supernovas are rare, occurring about once every hundred years per galaxy. Most of the supernovas we see are in other galaxies. This is a good thing, because a nearby supernova (within about 100 light-years) could kill us with the neutrino flux.

By the way, we are “on the verge” of building gravity telescopes, which could detect such things as binaries consisting of two black holes or two neutron stars, which don’t emit radiation but do emit powerful gravity waves. The basic principle is to very carefully measure the distance between two masses. If that distance decreases, that means a gravity wave is passing through, changing the shape of space.

After a supernova, if the remaining stellar core is less than 3 solar masses it becomes a neutron star, with all the protons and electrons smashed into each other to create an incredibly dense solid mass of nothing but neutrons. As the core collapses, angular momentum conservation makes it spin faster and faster, with a period of a few milliseconds. The same collapse amplifies the magnetic field by a factor of 10¹². Plusars (objects that pulse rapidly in the optical and radio bands) are believed to be rotating neutron stars, the magnetic pole of which is not aligned with the rotational pole. Every time the magnetic pole points in our direction we see a pulse. It may be that all neutron stars are pulsars, but we can see only the ones where the beam from the pole happens to shine on Earth. Some pulsars wobble as well as pulsing, indicating the presence of planets.

If the core is greater than 3 solar masses, its gravity is greater than the forces within the atom and collapse continues past the neutron star phase. There is no known mechanism to halt the collapse of a compact object of more than 3 solar masses. It keeps collapsing down to a single point: a singularity, or black hole.

Escape velocity from the surface of an object of given mass goes up as the object gets smaller and denser. The point at which the escape velocity is equal to the speed of light is known as the Swartzchild radius. If the object is any smaller than this it doesn’t matter. The Swartzchild radius is the “event horizon” beyond which nothing can ever be detected. This radius scales linearly with the mass of the object (3km for an object the mass of the sun, 30km for an object of 10 solar masses… a galactic-core black hole of 1.5 billion solar masses has an event horizon as big as Saturn’s orbit).

Black holes, it is said, have no hair. This means that they lose almost all of the characteristics they had before they became black holes. The only characteristics left are mass, angular momentum, and maybe electrical charge. Electrical charge is a maybe because it’s thought that a charged black hole will quickly attract enough matter with the opposite charge to neutralize it. A black hole’s angular momentum is interesting because a rotating black hole will drag the fabric of space around with it, a phenomenon known as “frame dragging.” Even though black holes do not emit anything, we can detect them by their effects on objects around them, or by gravitational lensing of the light coming from behind them.

Because of general relativity, a clock falling toward a black hole will appear to an outside observer to slow down, and stop as it passes the event horizon. At that point the light from the clock is red-shifted, meaning that it gradually fades from view. I don’t completely understand this. However, from the clock’s perspective the event horizon is undetectable (it’s like driving past the point where you don’t have enough gas in your tank to return home). However, in practical terms, long before it reaches the event horizon the clock will be torn apart by tidal forces. This phenomenon is called “spaghettification” because the object is “stretched into spaghetti” but this is far too tidy… in reality the object is ripped to pieces because every piece of it is being pulled either up or down relative to every other piece.

One last bizarre astronomical phenomenon: gamma-ray bursts (GRB’s). These are short (a few seconds) intense bursts of gamma rays. They were first detected by the military, who were looking for space-based atomic explosions. They are thought to be jets of radiation from “hypernovas” (deaths of very massive stars over 25 solar masses) in galaxies billions of light-years away.

As detailed as that was, I’ve left tons out. I can barely take notes as fast as the slides go by. This really is Astronomy 101 in a week, but I’m having a ball.

And even while I’m in Laramie, assiduously not writing, my stories are still out there and working. I just sold a story (to a market whose name I am not yet at liberty to reveal), and “Titanium Mike” will be podcast at StarShipSofa. More details as they become available.

Launch Pad is Astronomy 101 in a week. Some of us are already getting a little crispy around the edges.

Steve Gould has a cute tiny Asus “eee” laptop. I have discovered that you can get Mac OS X to run on it. ::wants::

Mike Brotherton started off the day with some introductory remarks. Observational astronomers, he says, are night owls; theorists are the ones who schedule 8am classes. He revealed that in academia it’s standard to pay for publication of your accepted papers ($150 a page or so); this helps keep the academic journals afloat. He also shared some useful URLs, then gave us a lecture on the electromagnetic spectrum.

Almost everything we know about the universe outside of the Earth (except for some moon rocks and space dust) comes to us in the form of light and other electromagnetic radiation. He explained the relationship between frequency, wavelength, and the speed of light, and how light refracts and is broken into the spectrum by a prism because the speed of light in glass is lower than it is in air and varies according to the wavelength (the frequency stays the same, but the wavelength changes as the velocity of the wave goes down). Light is also a particle, of course, and the energy of each photon is determined by its frequency. This isn’t the same as the intensity of the light, which explains why you get sunburn from high-energy UV photons but no harmful effect from even a very intense green light.

“Black bodies” are objects that absorb light equally at all frequencies. These objects also emit light at all frequencies when they are hot. The term “black body radiation” refers to the characteristic spectrum of such a body, which peaks at different frequencies depending on its temperature. The total amount of energy emitted also depends on the temperature — if you double the temperature (measured in degrees Kelvin, i.e. degrees above absolute zero) you increase the energy by a factor of 16!

Telescopes come in two basic flavors: refracting (lens) and reflecting (mirror). Reflecting telescopes are lighter and don’t have chromatic aberration (the red and blue fringes you can see on bright objects when you look through the edges of thick glasses like mine), but the focal plane where the image appears is on the same side of the mirror as the object being observed — this is not much of a problem in real life, you can put the sensor there, or a mirror to redirect the image somewhere else, without interfering with the telescope too badly. Reflecting telescopes are also much easier to make big, and the bigger (in diameter) the better.

Modern professional telescopes use adaptive optics (tiny rapid changes in the mirror to compensate for atmospheric disturbances) and long-baseline interferometry (using several small telescopes to simulate a much larger single telescope) to achieve results nearly equivalent to space-based telescopes. However, space-based telescopes can see frequencies no ground-based telescope can see through the atmosphere, including infrared and X-rays.

Danny Dale then gave us a lecture on dust in space (say it with me: “Duust… iiiinnn… SPAAAAAACE!”) which was reasonably interesting, but as much of the presentation was seemingly meant for other astrophysicists (lots of charts) I didn’t get as much out of it as I would have liked.

Jim Verley led us through a hands-on exercise in which we got to look at glowing tubes of several different gases through diffraction gratings, trying to identify the gas by comparing the spectral lines we saw with charts of several common elements. The exercise was very cool and a lot of fun (I have never seen a band of pure teal light before), and clearly showed us that the difference between theory and practice is always smaller in theory than it is in practice. I was reminded of the classic Electron Band Structure In Germanium, My Ass.

Next up was Jerry Oltion with a couple of exercises in back-of-the-envelope calculation. He started off with an easy one: how much does a cow weigh? The answer, no shit, started off with “posit a spherical cow of uniform density…”. The next question was “if we want to build an accurate scale model of the solar system, including Pluto, inside this 30′ long classroom, how big is the sun, how large are the planets, and how far are the planets from each other?” Jerry brought an assortment of spherical objects to help visualize this (“I have the minor planets here in a bag…”).

We started off with a beachball-sized sun, which makes the Earth a 1/10″ diameter BB 100 feet away; Pluto would be an insignificant speck 4000 feet away (nearly a mile!). From there we made the sun smaller and smaller (softball, tennis ball, ping-pong ball, marble…) until we finally got down to a 0.9″ mustard seed. At this scale the solar system (well, not the diameter of the solar system, but all the planets strung out in a line to scale) just fits in the classroom. Earth is a tiny speck 9″ away, Jupiter is smaller than a grain of salt at 45″ away, and Pluto is an even tinier speck 30′ away. There’s a whole lot of empty space in the solar system. Furthermore, at this scale Alpha Centauri A and B would be a pair of mustard seeds 20-30′ from each other… 31 miles away!

The width of your finger held at arms’ length is about 1 degree of arc, by the way.

The final exercise was to view the space station docking scene in 2001 and determine its gravity, using the equation v²r = g. The station rotates once per minute and, based on the heights of the people visible in some windows, is about 150 meters in radius. This means the circumference is about 1000 meters, so v is 1000 meters per minute, which yields a simulated gravity about 1/6 of Earth’s — the same as the moon (though the people inside move as though the gravity is Earth-normal). The very tidy numbers suggest that Arthur C. Clarke told the special effects guys exactly what to do.

I had a lot of fun with the back-of-the-envelope calculations. My father did this sort of thing with me all the time when I was a kid. Some other members of the workshop were left behind, though. I imagine they must feel the way I feel when I see tanned and fit people on sailboats who just hop into the water and swim to shore for lunch.

The day ended with a party at Mike Brotherton’s house, where we chatted with members of the UWyo astronomy faculty and saw the Milky Way (faintly) and a couple of meteors. Tomorrow night we go to the big WIRO telescope up on the mountain.