Friday, March 28, 2008

Gamma Ray Bursts

3/30/08 – 4/5/08
by C. Zaitz

Even though we think of the sky as having countless stars, it turns out we can only see several hundred of them due to light pollution. In fact, our Milky Way galaxy contains several hundred billion stars. Only in very dark skies can you see anything beyond the Milky Way. Until recently, our sibling galaxies, the Triangulum and Andromeda, were the most distant objects visible to the naked eye, at a distance between two to three million light years. Recently, something even more distant was seen. Though it was only slightly brighter than the faintest stars visible to us, it was very distant, and very old, light. At a staggering seven and a half billion light years away it was still seen, if even for seconds, and if you knew where to look.

What was this fleeting image? It was a bright gamma ray burst. Gamma rays are the most energetic form of “light” or electromagnetic energy. Gamma rays are produced by all stars, but when a huge star dies, it often produces prodigious amounts of them as it collapses. Astronomers think that these gamma ray bursts we see all around us are the relics of the deaths of some of the very first stars formed in the early universe. When they die, they go out with a big flash.

The incredible thing about gamma bursts we detect is that they are all very distant, but incredibly powerful and bright, much brighter than anything known in the universe. But they are not bright in all directions. The reason they can show up looking so luminous after seven and a half billion years of travel in a stretching universe is because the energy is bundled into relatively narrow columns. The energy streams out like a beacon from a lighthouse and if earth happens to lie along its route through the universe, we will catch a glimpse of it.

Astronomers are very interested in spying gamma ray bursts because they could tell us more about the early universe. Bursts of high energy rays are very harmful to humans, so it’s providential that air stops gamma and x-rays from getting to us. But it also makes them hard to find. Currently NASA has a telescope in orbit called Swift that scans the universe for gamma ray bursts. The problem with gamma rays is that they are much more energetic than visible light waves, and they don’t give a very accurate image of what they are detecting. It’s like trying to draw a picture using a shotgun rather than a pencil. In order to pinpoint where the bursts come from, we have to coordinate space and earth telescopes. So astronomers on earth are tied into Swift’s detectors. Once the gamma rays are detected, astronomers know about it and telescopes on earth can search the same area for visible light, which sometimes accompanies the bursts. Once we find them, we can study the information the bursts give us and map them.

Even though the bursts aren’t around for long, they do give us an incredible look at our past, into a time where the universe was dominated by giant hydrogen stars and was much smaller than it is today. It’s a universe that is continually changing, and revealing itself to us a burst at a time.

Wednesday, March 19, 2008

Space Flight

3/23/08 – 3/29/08
by C. Zaitz

Do you ever look at a bird and wonder how it flies? Or even better, wonder why you can’t? I wondered that the other day watching a hawk swooping and scooping air with its wings. I remembered Icarus of ancient mythology, the man who wore wings so he could fly. The higher he went, the more his giant wings made of wax and feathers melted from the high temperature of the sun.

In modern terms, the story makes no sense at all. First, if Icarus was confined to flying in the sky, he would have gotten colder, not warmer, as he flew higher. Second, if he had actually broken free and reached escape velocity by flapping his home-made wings, he would also have escaped the means of his flight- air pressure! Birds and planes rely on moving air to stay aloft. In space, there is no air, and thus no flight by wing. But the Greeks didn’t know this, and Icarus tumbled to earth with the melted wax and feathers all akimbo, a testament to man’s hubris and the punishment for flying too high.

Nature may not have gifted us with the ability to fly, but she did endow us with giant brains to figure out how to build devices that fly. In space, we have to use different principles to get around. One elegant solution was proposed long ago by Johannes Kepler. He noticed that comet tails were pushed back away from the sun by some force, and proposed that humans could catch that “breeze” to sail the solar system. Centuries later, the idea was proven true. Pressure from photons streaming from the sun can actually accelerate a thin, lightweight material, like a solar sail, to speeds that eventually could outrun our best traditional rockets. The key to their success, however, is patience.

If our traditional rockets are hares, solar sails are the tortoises of space travel. Since they are collecting ephemeral starlight, it takes a long time to get up a full head of steam to go fast. It’s a continual acceleration, unlike traditional rockets that blast off in a hurry but eventually run out of fuel. It may take a while to get “sailing”, but once it does, it will win the race!

Due to the nature of the slow acceleration, solar sails may not be suited for certain types of space travel. But there are so many benefits to using sunlight to propel a spacecraft that there are companies involved in creating materials and designs for commercial use. Launch rockets can be much smaller and more efficient to get the sails off the ground. The sails themselves don’t need fuel other than what they get from the sun. They can be cheaper, faster, easier, and create less waste.

It turns out that solar sails would need to get pretty close to the sun to go fast enough to travel large distances quickly. Like Icarus, they would swoop near the sun, but unlike him, they can use the energy and gravity to swing back out and go flying through the solar system. Perhaps one day, in the not so distant future, our night sky will be filled with sailing ships, off to distant worlds, using the “winds” of light and the wings of modern technology to fly.

Until next week, my friends, enjoy the view.

Wednesday, March 12, 2008

Stars and Daffodils

3/16/08 –3/22/08
by C. Zaitz

Just as the snow is melting to reveal the buds in the ground and on the trees, the winter night sky is drifting into the sunset, making way for the spring stars. We can still see the pretty set of constellations that make up the Winter Circle, but as we continue our orbit, the sun will be in front of those constellations in the coming months. Let’s take a last, lingering look at them.

I will miss the mighty Orion who watches over us on our quick trips between warm car and warm house. If you wink at him, he seems to twinkle back with his saucy grin and gleaming sword, his broad shoulders marked by the stars Betelgeuse and Bellatrix. The tilt of his belt leads the eye up to his nemesis, Taurus the Bull, off his western shoulder. Taurus’ bright eye is the star Aldebaran. It has a definite reddish tinge, as if Taurus was pawing the ground with his hoof and staring Orion down with an angry, bloodshot glare.

If we slide our eyes back to Orion’s belt and continue east, we find the bright blue-tinged beacon Sirius, in the constellation Canis Major, “the big dog.” Procyon is a star in the “little dog” Canis Minor above it, and still further above are the Gemini twins, Pollux and Castor. Above and to the west shines the bright star Capella, nestled in the five-sided constellation Auriga, who rides his chariot high over the winter sky carrying kid goats in his arms. Then back down to Aldebaran, “the follower” in Arabic, who seems to be following the ever delightful and lovely “Seven Sisters” or the Pleiades across the sky. It’s a familiar and comforting tableau; a collection of images that I look forward to seeing, even if it is a brief glimpse between destinations.

Springtime brings a changing scene. The sun lingers in the sky longer, so the stars come out later each night. Leo the Lion takes center stage not long after sunset. His stars look like a backward question mark with a little triangle marking his backside. Leo has a visitor this spring, the giant ringed planet Saturn. It will be drifting through the constellation, and its orbit will take it past the brightest star in Leo called Regulus. Regulus is a form of the Latin word Rex, which means king. I can really imagine a regal, burly, golden-maned lion, lying on his belly, paws curled under, watching over us all night long. Leo used to have a bushy tail, but it has long been severed to make a small constellation with the odd name, Coma Berenices. Coma means “hair,” and the tuft, rather than being the end of Leo, became the symbol of the crowning glory of Queen Berenice, wife of Ptolemy III of Egypt. She bobbed her hair so she could offer it to the goddess Aphrodite to ensure the safe return of her husband from battle. Whether it was her husband’s skill or her coiffured offering, he did return safely, and the locks were put in the sky.

The spring equinox is on March 20tht this year, and as it approaches we can simultaneously watch the march of the constellations and the unstoppable budding growth of new life.

Until next week, my friends, enjoy the view.

Thursday, March 06, 2008

The Nature of Math

3/9/08 – 3/16/08
by C. Zaitz

I’ve done many different things to make a living, but I never thought I’d be teaching math to anyone. Frankly, I wasn’t a big fan of math classes in school, though I’ve taken my share of them to get to the “good stuff” in physics and astronomy. I found some math teachers to be in a “mathy” tower, using a “mathy” language that was hard to understand. But I needed the tools of math, like poets need a language to do their art. Without math, physics and astronomy are only descriptive. Without it, we would never have been able to pin down the age of the universe, much less balance our checking accounts. So we have to do math.

I’m teaching it only temporarily, but already I have a new appreciation for the language of mathematics. Math never wanted to be in a tower, and never wanted to be a separate language. Math permeates everything. Nature has a deep friendship with math- it uses it to design itself. Leaves, seashells, flowers and pinecones all reflect specific mathematical relationships.

Not only did nature use math in its designs, mathematical relationships have allowed us to unlock the mystery behind why the planets orbit they way they do, to understand the relationship between a star’s distance and brightness, and even to figure out how fast we are moving on the surface of our planet, earth.

I’m not saying the language of math is always easy, but it’s not always hard either. Kepler’s laws tell us that the period of a planet is related only to its distance from the sun. That’s beautiful, but it requires finding squares and cubes of numbers. Thank goodness for calculators. To figure out how bright a star is, you can use the inverse-square law. That sounds complicated, but nature says the further you are from a source of light, it gets dimmer faster than you’d think. If you are twice as far away from a star as your neighboring alien, you will experience only a quarter as much light. The cool thing is that the law works for other things, like gravity and magnetism! The math is fairly simple, but it has far reaching import.

To find our speed standing still on the surface of the earth, we need to know how fast the earth is spinning. 2 pi divided by 24 hours times the radius of the earth yields around 1,000 mph! That’s how fast the ground under our feet is moving (at the equator.) And so are we. But it takes physics to explain why we aren’t flying off the planet if we’re traveling so fast. We call it inertia- we’ve all been going that fast since we were born, and the only way we’d feel it is if the earth sped up or slowed down abruptly. Math coupled with science is the most powerful tool we humans have.

For me, the beauty of math has been about how useful it is. But the Golden Ratio is a famous relationship between ratios, and its proportions are pleasing to us. Artists have used it throughout history in famous paintings. There have been philosophers who suggest that numbers have been our connection to the eternal. But I’m not that ambitious with math. If I can just get my students to figure out how high a flagpole is by measuring its shadow and using trigonometry, I’ll be happy.

Until next week, my friends, enjoy the view.