The Lava Connection
The Earth >
I had the great privilege to go to the big island of Hawaii a couple weeks ago with my family and astronomy club. Of course, we went there to visit the great telescopes on Mauna Kea, and, well ... maybe a beach or two.
 If you get a chance to, visit our Hawaii section to see plenty of exciting videos of the FirstLight Astronomy Club almost being devoured by lava. Just kidding, school board! |
But one of the highlights of the trip was to stand just feet away from thousands-of-degrees hot flowing lava at Kilauea National Park. What on Earth does blisteringly hot molten rock have to do with astronomy?
Everything.
Did you ever wonder why lava even exists in the first place? Why are we floating on the hardened crust of a melted planet? Where did all that heat come from? For answers to those questions we go out to the stars --- the giant stars.
Regular readers here may recall that there is a virtual zoo of stars up there. From very small, about a tenth the mass of our sun, to probably over 100 times more massive than the sun.
The big ones will burn their fuel fast and furiously, dooming themselves to a quick life and a spectacular death.
Now comes the thinking cap time. When a big star goes boom, it is destroyed in the now legendary supernova. This explosion is so powerful it can smash together the tiny nuclei of carbon and silicon and magnesium and others that made up the innards of the star. These new, bigger critters, like uranium for example, can be found in the lower parts of the periodic table, if you remember your chemistry.
But not all the nuclei like their new extra-large size. The protons and neutrons forced together in the explosion might be unstable and begin to break apart, becoming "radioactive." It's not exactly that they asked to be born that way, after all.
When they do fall apart --- a process called nuclear fission in the biz --- they give off a lot of energy. This is the same sort of energy, nuclear energy, which we tap into with nuclear reactors and fission bombs.
Now, finally, the lava connection.
When the supernova explosions in a particular place in a galaxy spew their newly formed unstable fissionable guts all over the place, the material doesn't just go away. Trillion of tons of this dusty material, and non-radioactive new material as well, can be vacuumed up in the formation of new-generation stars and their planets.
When our sun was formed about 5 billion years ago, there was enough debris from at least two nearby supernovae that it collected in a disk around our baby sun to form the planets and comets and asteroids.
Some rocky bodies, like our own planet, still have enough of the radioactive material in them to keep them warm. I mean really warm. I mean smarting hot.
The beauty of all this is profound. The solid crust you're sitting on now is riding on vast gooey oceans of this melted rock. This allows plate tectonics to move and recycle the crust, giving us mountains and hills and ocean basins and tremendously fertile topsoil --- a perfect landscape for life.
And no other known planet currently has this life-enhancing phenomenon. All the other planets are now essentially dead --- geologically speaking.
If you get a chance to visit a lava flow, do. You'll witness firsthand the end sequence of a tightly designed set of cosmic phenomena, and a great reminder of the beautiful uniqueness of this home of ours.
Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com.
Posted by Administrator at 2003.03.30 01:41 PM | Comments (0)
Explosive Measurements
Science >
This is the concluding article of the suspenseful best-selling action trilogy: Measuring the Fantastic Distances of Space. The first two were pretty straightforward; this one can get weird.
You may recall that for close-by stellar critters we use "parallax." For objects farther out we utilized the cosmic object called a Cepheid variable. You can still read those articles at http://firstlightastro.com/icolumn.
But those methods only took us to millions of light years out. Problem? The visible universe is billions of light years - thousands of times bigger - in all directions.
How can we measure things out to such great distances? One trick is to use another relatively reliable source of light --- the supernova.
Recall that a supernova is the explosive death of a gigantic star. One type of supernova --- Type Ia --- pop off everywhere in the universe with pretty much the same amount of light as each other. And they are really, really bright; as bright as the galaxy they resided in before their timely death.
If we know how much energy they are supposed to throw when they blow, and then measure the amount of energy that actually manages to make it this far, we can estimate how far away they were (via last week's inverse-square law).
These explosive bad boys can help us measure distances out to about 8 billion light years!
But there's a cosmic ruler that can take us way out there, to the edge, 13 billion light years away. This is the special child in the family of measurements. And to understand it in this extra short explanation will require an extra large Thinking Cap. Ready?
Through the combined efforts of three great astronomers --- Vesto Slipher, Milton Humason, and Edwin Hubble --- it was discovered early last century that the universe was expanding!
They had discovered that essentially all other galaxies were moving away from us. But the closer ones were moving slowly away. Ones farther moved faster. The farthest galaxies were racing away from us. The only explanation of this was that the universe was getting bigger.
Imagine a deflated balloon with dots drawn randomly on the surface. As one blows up the balloon the dots all move away from each other. Focus on any one dot --- any dot you want --- and you'll discover that other dots close to it are moving away slowly, the dots farther away are moving faster.
The beauty of it is this: Say a dot at a certain distance is moving a certain speed away from your Home Dot. Then a dot twice as far will be moving away twice as fast. A dot three times as far will move away three times faster.
Now without getting bogged down in the math, suffice it to say now that we can do the same basic thing with galaxies. If we know how fast the universe (balloon) is expanding, and we can measure how fast a certain galaxy (dot) is riding away from us (the Home Dot) on that expanding universe, then we can estimate its distance.
Now, it's considerably more uncertain than our balloon example. Getting a handle on how quickly our universe is expanding is one of the great challenges of modern-day astronomy.
But as techniques and measuring devices continue to improve at amazing rates, we're starting to get some very precise measurements. And as we get more precise in our distances we can start building giant maps of the universe.
And just as we can learn a lot about the history of planet Earth by looking at a detailed globe, we can learn much of our universe by studying the Great Map of the Heavens.
Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com.
Posted by Administrator at 2003.03.15 01:45 PM | Comments (0)
It's Hip to be Inverse-Square
The Universe >
In our last column we delved into how astronomers deal with the great distances inherent in the discipline of astronomy. The method called parallax helped us find distances to stars about a thousand light years or so away.
But how do our astronomer friends deal with greater distances, out to hundreds of thousands or even millions of light years?
First let me introduce you to a concept that really needs no introduction. You already know from experience that as a light source, like a lamp, gets farther away, it gets dimmer, too.
But I can put numbers on it; scientists love that. Suppose our lamp at one meter puts out 100 units of energy. If I move my lamp to twice the distance, two meters away, a funny, unexpected thing happens. I don't get half the light from before. I get one-fourth the light --- only 25 units!
The inverse-square law of physics tells me that if I go out to two times the distance, I inverse that number --- one over two --- then square it. That gives me one-fourth.
If I go to three times the distance, three meters for our example, I will get one-ninth the original energy --- about 11 units. Go to four times the distance, my light detector picks up only one-sixteenth the light. And so on.
In fact, put the lamp at any distance you want. My light detector, my calculator, the inverse-square law, and I can tell you how far the light is.
We can do the same with stars. If we are confident about how bright a star should be, and are confident about the amount of starlight picked up in our detector, then we can be confident in using the inverse-square law to find its distance.
For example, if we know the "stellar classification" of a given star, exactly what type of star it is, then we know how much energy is spewing out of it. Our detector will tell us how much energy we are actually receiving from the distant star. A couple quick flicks of the calculator can help us find that creature's distance.
But using a star's class is good to only about 30,000 light years or so.
Farther out we need a special star --- a Cepheid variable. Don't be put off by that astrospeak name. A Cepheid is merely a star that brightens and dims regularly, like a clock. The beauty of these distant distance tools is that they vary in brightness in a very predictable way.
Breathe as you read this (always a good idea). Take several long even breaths, deep in, deep out. This is like a longer period Cepheid. They brighten as they contract, dim as they expand. And they are brighter than their brothers, the shorter period Cepheids.
Those stars are like taking a series of short breaths, like a pant. Since they have such a quick succession of getting bigger and smaller, they don't have a chance to brighten up as much as their longer period brothers.
Astronomers can tell how bright Cepheids should be just based on their "breaths." And again, if we know how bright they should be, and our light detectors tell us how bright they appear to be, we can use the inverse-square law to figure out their distance.
And Cepheids are all over the place, in galaxies near and far. Our instruments are now sophisticated enough to use Cepheids to calculate distances to galaxies 100 million light years away!
But what about galaxies billions of light years out? Sorry, you'll have to wait!
Until next time, clear skies!
Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com.
Posted by Administrator at 2003.03. 2 01:48 PM | Comments (0)