About Carolyn L

Carolyn coordinates the Science on Stage outreach program at HMNS and will blog about science toys and experiments, logic puzzles, and whatever else seems interesting at the time.

Educator How-To: Crystals, Geometry and Chemistry

Math is beautiful and inescapable. Especially in nature, patterns and equations just keep showing up.  The path of an orbiting planet, the growth of a nautilus, arrangements of leaves on a stem, the efficient packing of a honeycomb; we can find rules and algorithms and make predictions from them.

Crystals, with their obediently repeating structure, are an elegant manifestation of the ‘rules.’  To be a crystal, your building blocks (atoms, molecules, or ions) must follow patterns over and over and over and over and over.  Atoms, being predictable, simply do what their chemical properties and the conditions (temperature, pressure, etc.) indicate.  So what exactly does it take to go from a mess of elements and compounds to this[picture of green “Crystals of India” crystal specimen] example from the Crystals of India exhibit at HMNS Sugar Land?

If you’ve ever tried making rock candy from sugar water or ornaments from borax solution, then you have some idea what it entails: something dissolved that is capable of making crystals has to slowly come out of solution – usually the longer you give it, the bigger it can grow and the slower it grows, the more perfect the crystals.

Freezing water into ice also gives you crystals; they just don’t stick around and let you handle them conveniently at room temperature. Water and solutions in water aren’t the only way to get crystals; molten rock cooling (slowly) can also give crystals, but that’s a little tricky for home experimentation.

So time is your friend for crystal growth, pressure is a factor, and it needs to be easier for atoms to attach to the forming crystal than to stay in solution.  Having a solution that is saturated or supersaturated so it can barely hold all of the dissolved material helps. It also helps to have places for the crystals to start forming; a tiny ‘seed’ crystal or sometimes even just a rough spot on a surface can provide the nucleation sites to kick off crystal growth. Are there other ways crystals and the things we consider ‘gems’ can form? Yes!

For those of us with shorter attention spans, a cool way so see the process is with crystallizing hand warmers – a pouch holds a saturated solution of sodium acetate. When you flex a metal disk inside the pouch, you kick off a chain of crystallization and end up with solid material (and released heat energy).  Because the process is so fast in the hand warmer, the individual crystals are very small and jumbled up (polycrystalline); oriented in all different directions, and as a mass they are opaque (light is refracting all over the place) and relatively dull rather than shiny and smooth as slower-forming large crystal faces can be.  The structure of most metals is also polycrystalline, and things like plastic and glass (even the kinds misleadingly labeled “crystal!”) are amorphous.

The external crystal shapes we see are related to the internal structure – there are a lot of different ways atoms can pack together.

Practically, there will always be some disruption in a crystal structure, no matter how perfect it may appear, which allows for some very cool effects – crystals “twinning,” impurities that alter the color; the reason ruby and sapphire (both corundum crystals) appear different.

Crystals aren’t always pretty! Sometimes we want to prevent crystallization to avoid things like kidney stones, but crystals are useful for all kinds of things; optical equipment and lasers, X-ray crystallography to figure out structures of proteins (and once upon a time, DNA), and silicon chips used in electronic devices. 

Whether you prefer your crystals practical or decorative (photo of white spikey crystal from Crystals of India), they are amazing!

Can’t get enough crystals? Check out the Crystals of India exhibit at HMNS Sugar Land (free for members!)

 

 

Glow on, get happy! Join HMNS this Friday for a fun-filled night of light at LaB 5555: GLOW

Whether they’re toys that shine in the night, black lights, glow sticks or fireflies, things that produce an eerie glow are fascinating. Give a kid a glow-in-the-dark toy or paper her ceiling in dimly shining plastic stars, and she will be occupied forever. She’ll find ever brighter lights to charge them up, ever darker places to view them for maximum glow effect, and generally love exploring how it all works.

You know this; you were that kid. So what’s the deal with the glow?

Enjoy a sip of the galaxy -- learn how to make this glow-in-the-dark cocktail at Neatorama

Learn how to make this amazing looking glow-in-the-dark cocktail over at Neatorama

It’s 10 p.m. Do you know where your electrons are?

While there are several “flavors” of things that glow, they all have something in common: Things glow because photons are emitted when “excited” (at a higher energy state) electrons drop back to a lower, more stable state. Aside from promising them a pony or a tour of CERN, there are several ways to get your electrons excited.

In chemical glow sticks, a chemical reaction excites the electrons. This process is called chemiluminescence. Glow sticks are an excellent way to experiment with reaction rates and temperature. If you want the reaction to last longer, follow a kid’s advice and put the glow stick in the freezer or in ice water so the reaction slows down; it’ll take longer to use up the chemicals in the glow stick. The trade-off is that because the production of photons is also slower, a cold glow stick is dimmer than a warm one.

Fluorescence is like light recycling. Fluorescent rocks, laundry detergent additives, paint, and even some animals can re-emit light after something shines on them. Usually we’re talking about things getting hit with ultraviolet or ‘black’ light and re-emitting within the visible spectrum. This makes sense because as you progress along the spectrum of electromagnetic radiation, visible light is a bit lower in energy than ultraviolet light — you can’t expose something to lower energy red light and get it to fluoresce in UV, for example. Fluorescent things certainly fluoresce in daylight, but not enough to outshine the ambient light, so they’re most noticeable under a black light in an otherwise dark space.

Phosphorescence is a lot like fluorescence but stretched out over time — a slow glow. So you can shine light (visible or UV) on a glow-in-the-dark star and it re-emits light, too, but over a lot more time, so the glow continues for minutes or hours before it completely dies out. If you have a glow-in-the-dark toy or T-shirt, try “charging it up” with lights of different colors or intensities and checking out the glow that results.

Nature glows

Fireflies produce and use their own chemicals, luciferin and luciferase, to dazzle and attract potential mates — and sometimes to lure prey. A surprising number of marine critters are bioluminescent, too, like dinoflagellates (plankton) that glow when disturbed, the angler fish, and some squid (perhaps they are blending in with starlight from above). Headlines occasionally announce a new genetically engineered “glowing” kitten, rabbit, plant, sheep, etc., but they are almost always talking about fluorescence instead of bioluminescence, so the light is only seen when the animal is placed under ultraviolet light. (One useful application of this is the ability to track a protein related to a certain disease by getting the introduced gene for Green Fluorescent Protein (GFP) to link to the gene for the protein of interest). Some animals like scorpions and jellyfish (the original source of GFP) fluoresce naturally.

Cheap thrills

Sugar and adhesives can exhibit triboluminescence, in which friction or fracturing produces the light. This one is great to try out at home; you just need Wint-O-Green Lifesavers®, transparent tape and a very dark room (a buddy or a room with a mirror is helpful for the Lifesavers portion). Dr. Sweeting (that’s her real name) has more detailed instructions and explanation, but the big idea is that a tiny, but visible, amount of light is emitted when you peel tape off the roll and when you bite into the candy, crushing sugar crystals against each other. The wintergreen oil even improves the effect by fluorescing!

Are there any other kinds of luminescence? Yes! Incandescence, piezoluminescence, radioluminescence, etc. But that’s enough fun for one post. Go try out triboluminescence!

Just can’t get enough? Make sure to come early for the educational portion of HMNS’ LaB 5555 this Friday for more GLOW fun, and learn all about the science of what gives things light. I’ll be there doing demos to light up your night. For tickets and more info, click here!

2012: Did the Maya Predict an Apocalypse?

For the last 2 years, the Astronomy Department of the Houston Museum of Natural Science has searched and researched Maya ruins and writings for connections between the Mayan calendar and the ability of Maya astronomers to predict future events.

To record the passage of time, the Maya developed a 260-day ritual cycle, made up of thirteen numbers and twenty names. With this continuous running cycle, they could predict future events like the harvesting of crops and the birth of children. The Maya kept a second 365-day solar calendar of 18 months, each lasting 20 days, plus 5 extra days to complete the year. This calendar determined the growing season and the annual return of the rains. For longer time periods the Maya used a 5-number Long Count. On December 21st, 2012, for instance, this Long Count has a new beginning as the date changes from 12.19.19.17.19 to 13.0.0.0.0. This is similar to the change from 1999 to 2000 in our modern calendar and is the cause of much 2012 speculation.

Great Temples
The homeland of the Maya stretches from southern Mexico to northern Central America. Our new planetarium show, 2012: Mayan Prophecies (Now Showing!), explores the great Maya cities of Uxmal, Chichen Itza, Tikal, and Palenque. For survival, the Maya created these great urban centers to store rainwater through the dry season and built observatories to determine when the annual rains would begin.

The Castillo pyramid in Chichen Itza is a temple to the feathered serpent god Kukulcan. Each of its 4 staircases has 91 steps for 364 steps in all with a top step into the temple – one step for each day of the year.  According to legend, Kukulcan returns to his pyramid on the vernal and autumnal equinoxes, descending the staircase in an undulating shadow.

In the nearby Caracol observatory, astronomers watched Kukulcan, who appeared in the heavens as the planet Venus. Through motions of the brilliant Venus, they determined the will of Kukulcan and the time for human sacrifices to honor this sky god and give thanks for the rains he would soon send.

Tikal
photo courtesy of Raymond Ostertag

Tikal
The Maya carved the great city of Tikal out of the rain forest in the lowlands of modern Guatemala. In this city of up to 100,000, all water came from the sky. Tikal’s rulers cleared the rain forest, channeled the water in swamps to grow crops, and built cisterns and catch basins to store water during the rainy season. Tikal’s power depended on storing enough water to last until the rains returned each spring.

Five giant pyramids helped astronomers predict when the rainy season would begin. On December 21, for instance, astronomers on Temple 4 could watch the sun rise farthest to the south, over the Pyramid of the Jaguar Priest. From this date forward, they knew that the sun would rise a little more to the north each day. At the vernal equinox, the sun would always rise over Temple 1, an event that must happen before the rains could begin.

Palenque
In the foothills of Mexico’s southern mountains, lies the Maya city of Palenque. Blessed with abundant rain and flowing rivers, the artisans of Palenque had time to create some of the most elaborate and exquisite Mayan art and the most delicate of buildings. Here inscriptions describe the beginning of the Maya long count cycle and chronicle events far into the future, but no mention of 2012.

There has been a subtle change in the sky in the 1,300 years since the time of the classic Maya. Due to the wobble of Earth’s spin axis, different stars rise with the sun in each season.

For instance, at the time of the Maya, the glowing Milky Way band was above the sun at sunrise on the winter solstice.  Now in December, the sun reaches its lowest point at noon in front of a dark rift in the Milky Way, near the direction of the galaxy’s center.

Does this mean that galactic forces are now aligned? Did the Maya predict this alignment? We have no data to indicate that the Maya recognized the 26,000-year cycle that caused this alignment. There is no documented connection between the Earth-centered Maya cosmos and our modern universe.

Classic Maya civilization did experience a great apocalypse, but it occurred long before the Spanish Conquest.

For over a millennium, the major cities of the Maya have stood abandoned – deserted by their citizens, conquered by weather and reclaimed by the rainforest. At their culture’s height, many of the Maya faced the worst drought in thousands of years. It devastated a civilization that had cut down the rainforest to grow crops and destroyed urban centers that could not store enough water for their people. In less than a hundred years, over a hundred thousand Maya disappeared, leaving their parched cities and their withered fields, rejecting the divine right and Earthly power of their kings. By the thousands they returned to the rainforest and mountains to a sustainable population and way of life.

As we sense the fragility of our own culture today, we may discover a warning for 2012 in the ruins of these great Maya cities — silent sentinels, witnesses of the apocalypse of the Maya.

Explore pyramids towering above the rainforest, designed as observatories to follow the sun. Experience the apocalypse of the Maya and discover how our fate in 2012 may be foretold in our new planetarium show 2012: Mayan Prophecies. Check out the extended preview below!

Can’t see the video? 2012: Mayan Prophecies from HMNS on Vimeo.

Snow? In Houston? Really?

On Wednesday, four days after the HMNS Snow Flurry event, it was chilly and wet outside. I was snug in my office with a mug of cocoa and a toasty warm computer monitor when I heard a ridiculous story that we were supposed to see naturally falling snow by that evening. I naturally accused the bearer of this news of hopeful invention, if not outright lying, then checked a weather website and saw indications for ‘rain or snow showers’ that evening, but still I didn’t believe we would see anything interesting. “It will all melt on the way down — it’s not even supposed to get below freezing tonight!”

But of course I was wrong and we had the first snow Houston has had this early in the season since 1944! Allison took these pictures:

So what conditions do you need to form snow? Well, if you have the right lab and a research budget, you could grow snow crystals indoors! (‘Snowflakes’ can refer to individual crystals or (often) to agglomerations or clumps of many, many snow crystals.) If you need larger quantities, you can always create your own snow like ski resorts, but you still need much colder conditions than we usually have. Most of us, however, must wait for suitable weather conditions.

Need immediate gratification? You can always resort to making decorative paper snowflakes, or try a more high-tech option.

We may not see snow again this year, but if you’re curious about who else might be getting it soon, check out this 24-hour snow forecast map. Or see if your holiday travels will bring you a White Christmas.