Sometimes I complain about the earthly weather, but mostly I like to post about astronomy and space events. Hope you enjoy the articles.
By: Susie77, 1:12 AM GMT on May 01, 2008
The eta Aquarid Meteor Shower
Global Notes: This shower can be seen from both hemispheres--north and south..
The eta Aquarid meteor shower peaks this year on Monday, May 5th, and Tuesday, May 6th. The best time to look, no matter where you live, is during the hours immediately before sunrise. If you can, get away from city lights; you will see more meteors from the dark countryside.
2008 is expected to be a good year for the eta Aquarid meteors. The Moon is new, which means no lunar glare, and Earth is expected to pass through an unusually dense region of comet dust, driving meteor rates as high as 70 per hour in the southern hemisphere. Sky watchers in Australia, New Zealand, South America and southern Africa are favored. It is possible to see the shower from the northern hemisphere, too, but rates are reduced to less than 30 per hour.
The eta Aquarids are flakes of dust from Halley's Comet, which last visited Earth in 1986. Although the comet is now far away, beyond the orbit of Uranus, it left behind a stream of dust. Earth passes through the stream twice a year in May and October. In May we have the eta Aquarid meteor shower, in October the Orionids. Both are caused by Halley's Comet.
The eta Aquarids are named after a 4th-magnitude star in the constellation Aquarius. The star has nothing to do with the meteor shower except that, coincidentally, meteors appear to emerge from a point nearby. Eta Aquarii is 156 light years from Earth and 44 times more luminous than the Sun.
The constellation Aquarius does not rise very far above the horizon in the northern hemisphere, and that's why northerners see relatively few meteors. But the ones they do see could be spectacular Earthgrazers.
Earthgrazers are meteors that skim horizontally through the upper atmosphere. They are slow and dramatic, streaking far across the sky. The best time to look for Earthgrazers is between 2:00 to 2:30 a.m. local time when Aquarius is just peeking above the horizon.
Experienced meteor watchers suggest the following viewing strategy: Dress warmly. Bring a reclining chair, or spread a thick blanket over a flat spot of ground. Lie down and look up somewhat toward the east. Meteors can appear in any part of the sky, although their trails will point back toward Aquarius.
Eta Aquarid meteoroids hit Earth's atmosphere traveling 66 km/s.
Typical eta Aquarid meteors are as bright as a 3rd magnitude star.
By: Susie77, 2:41 AM GMT on April 26, 2008
(One of the last experiments done by the doomed astronauts of the Columbia).
The Physics of Whipped Cream
April 25, 2008: Let's do a little science experiment. If you have a can of whipped cream in the fridge, go get it out. Spray a generous dollop into a spoon and watch carefully.
Notice anything interesting? The whipped cream just did something rather puzzling. First it flowed smoothly out of the nozzle like a liquid would, and then, a moment later, it perched rigidly in the spoon as if it were solid. What made it change?
(While you're pondering this question, insert spoon into mouth, in the name of science.)
Whipped cream performs this rapid changing act because of a phenomenon called "shear thinning." When part of the foam is forced to slide or "shear" past the rest of the foam, the foam "thins." It becomes less like honey and more like water, allowing it to flow easily until the shearing stops.
Shear thinning occurs in many substances--e.g., ketchup, blood, motor oil, paint, liquid polymers such as molten plastic--and it is often crucial to how a substance is used. For instance, excessive shear thinning of motor oil is unwanted because it reduces the oil's ability to protect engines from wear, while shear thinning of paint allows it to flow smoothly from the brush but stay put on the wall. It also allows ketchup to flow from the bottle but not drip off your french fries.
Yet, for years, scientists have asked themselves the same question you just did: What made it change? The inner workings of shear thinning are not fully understood.
"Details depend on interactions in the fluid at the molecular level and those interactions can be devilishly complex," says fluid physicist Robert Berg of the National Institute of Standards and Technology. "Even for very simple fluids, fundamental theories have never been directly verified."
Until now. The first real-world confirmation of a theory for how shear thinning works in a simple fluid has come from an experiment that flew aboard the final flight of Space Shuttle Columbia.
"We showed that a leading theory is basically correct, " says Greg Zimmerli, Project Scientist for the experiment at NASA's Glenn Research Center. "This is an important step," adds Berg, the experiment's principle investigator.
Most of the data from the experiment, called Critical Viscosity of Xenon-2 (CVX-2), was beamed down to scientists on the ground before the shuttle's destruction during reentry into Earth's atmosphere. Remarkably, the hard drive from the experiment survived the disaster and was found amid the wreckage, and technicians were able to recover the rest of the data.
CVX-2 was designed to study shear thinning in xenon, a substance used in lamps and ion rocket engines. Xenon is chemically inert, so its molecules consist of a single atom -- it's about as close as you can get to the flying billiard balls of an idealized gas or liquid. Unlike whipped cream, which is made of long, complicated organic molecules, xenon would be relatively easy to understand.
"It's a simpler fluid for the theorists to try to grasp," Zimmerli says.
Simple liquids like xenon don't normally experience shear thinning. They're either thick or thin, and they stay that way. But this changes near the "critical point" -- a special combination of temperature and pressure where fluids can exist as both a liquid and a gas simultaneously. At their critical point, simple fluids are able to "shear-thin" (a verb) just like whipped cream does.
Xenon at the critical point resembles a hazy fog, a slurry of microscopic pockets of slightly higher or lower density. These tiny regions of varying density are constantly appearing and disappearing in a seething froth, giving the pure xenon some of the structural complexity of mixtures like blood.
CVX-2 had to be done in space: Critical-point fluids are easily compressed. On Earth they collapse under their own weight and become denser at the bottom. In orbital free-fall those differences vanish -- a key requirement for a good experiment.
To test shear thinning, CVX-2 adjusted the temperature and pressure in a small cylinder to bring xenon to its critical point, and then gently stirred the fluid with a nickel-screen paddle. By measuring how strongly the fluid resisted the movement of this paddle, the experiment could determine the xenon's thickness. CVX-2 searched for changes in this thickness as it slowly changed the speed of the stirring and the temperature of the fluid.
Results nicely matched the predictions of dynamic mode-coupling theory. "This more fundamental understanding could help us build better theories for shear thinning in fluids more complex than xenon," Zimmerli says.
That would be good news for, say, engineers who want to design high-performance oils for automobiles or manufacturers who would like to create liquid plastics with just the right shear thinning properties for a particular mold. The sky's the limit.
Whether it would be possible to improve whipped cream, however, is highly debatable.
By: Susie77, 1:09 AM GMT on April 25, 2008
(with apologies to Dorothy....)
By: Susie77, 12:37 AM GMT on April 23, 2008
For us here in the northern hemisphere, our Mother is waking from her winter's slumber. This morning she treated us (here in the midwest) to one of her concerts -- thunder, lightning, a spat of tiny hail... and the blessed rains.
I lay in bed and listened to her music and pondered on my journey here -- and how much better we have been treating our Mother in more recent years. I recall my father (back in the 50s) having to go to Pittsburgh now and then for conferences. My mother would despair when she saw his formerly white shirts when he came home-- they had turned grey from the filthy air. i remember lakes and rivers that you could only admire from afar -- up close, the shores were lined with human debris, barrels, stinking dead fish. My dad worked for a major chemical company. He thought nothing of coming home with their products and dumping them in our yard and gardens. My mother, far wiser and ahead of her time, would not let us kids go outside after his applications. Most of those chemicals have since been banned.
As a child, I only saw wild geese perhaps twice -- tiny specks far up in the heavens -- barely perceptible, only a faint echo of honking calls to signal their presence as they winged their way southward. Now, wild geese are often a nuisance. In fact, one glared at me today when I got out of my car at work!
I was an adult before I saw a bald eagle in real life -- at the zoo. Now, I can drive four miles down to the Mississippi River and see them fishing and raising their famiiles. I can walk a short mile and a half along the river to one of their nests. And that river? While I still wouldn't drink out of it, the only floating debris usually seen consists of branches and other natural material.
We still have a lot of work to do to clean up our Mother, our spaceship, our beautiful blue water world, our home Earth. We are making progress though! In just my short time here (geologically speaking of course), I have witnessed great strides in environmental awareness and protection.
I wish for all of you a marvelous personal journey on our trip around the galaxy. May we all leave this place the better for having sojourned here.
By: Susie77, 11:07 PM GMT on April 19, 2008
BUTTERCUPS AND GOLF BALLS
Towards the end of the golf course, Dave hit his ball into the woods and found it in a patch of pretty yellow buttercups. Trying to get his ball back in play, he ended up thrashing just about every buttercup in the patch.
All of a sudden . . POOF!!
In a flash and puff of smoke, a little old woman appeared. She said, 'I'm Mother Nature! Do you know how long it took me to make those buttercups? Just for doing what you have done, you won't have any butter for your popcorn for the rest of your life: better still, you won't have any butter for your toast for the rest of your life... As a matter of fact, you'll never have any butter for anything the rest of your life!!!
Then POOF! . . . she was gone!
After Dave recovered from the shock, he hollered for his friend, 'Fred, where are you?'
Fred yells back 'I'm over here in the pussiwillows.'
Dave shouts back, 'DON'T SWING, Fred; FOR THE LOVE OF GOD, DON'T SWING!!!'
By: Susie77, 1:58 AM GMT on April 18, 2008
Well, some nancy-pants whined and they took my previous post away regarding the golf game and the buttercups. So of course, I have an emergency back-up post! Enjoy.
Moses and Jesus were in a threesome playing golf one day. Moses pulled up to the tee and drove a long one. The ball landed in the fairway, but rolled directly toward a water hazard. Quickly Moses raised his club, the water parted and it rolled to the other side, safe and sound.
Next, Jesus strolled up to the tee and hit a nice long one directly toward the same water hazard. It landed right in the center of the pond and kind of hovered over the water. Jesus casually walked out on the pond and chipped the ball onto the green.
The third guy got up and randomly whacked the ball. It headed out over the fence and into oncoming traffic on a nearby street. It bounced off a truck and hit a nearby tree. From there, it bounced onto the roof of a shack close by and rolled down into the gutter, down the drain spout, out onto the fairway and straight toward the aforementioned pond. On the way to the pond, the ball hit a stone and bounced out over the water onto a lily pad, where it rested quietly. Suddenly a very large bullfrog jumped up on a lily pad and snatched the ball into his mouth. Just then, an eagle swooped down and grabbed the frog and flew away. As they passed over the green, the frog squealed with fright and dropped the ball, which bounced right into the cup for a hole in one.
Moses turned to Jesus and said, "I hate playing with your Dad."
By: Susie77, 12:39 AM GMT on April 17, 2008
So what, if anything, are you all doing to commemorate Earth Day this year? So far, our plans are to visit the Missouri Botanical Gardens in St. Louis. It was there, some 37 or so years ago, that I met and shook the hand of Dr. Barry Commoner, one of the founders of the modern environmental movement and ecological sciences. At the time, I just thought he was just another 'old guy' like my dad, who I was with. Imagine my surprise a couple weeks later when I saw his picture on the cover of Time magazine. :-)
Happy Earth Day, however you choose to observe it. I hope that you teach your children that all life on our planet is connected to all else, and that we are all fellow passengers on this lovely, lovely world.
By: Susie77, 12:57 AM GMT on April 06, 2008
April 4, 2008: The date was March 8th, less than a month ago. In a remote corner of Kansas, the sun was going down and the deepening twilight beckoned to photographer Doug Zubenel driving through the countryside. Something photogenic, he knew, was about to happen.
He turned his car onto an unfamiliar dirt road and proceeded into the sunset. "The brilliant sun did not allow me to see the cement railings on a bridge over a small creek. The next thing I knew, I had totaled my car!" Zubenel emerged from the wreckage, phoned 911, and while he was waiting for the tow truck to arrive, took the picture:
"It was a beautiful 1-day old crescent moon," says Zubenel. "It looked a lot better than my car!"
This perilous scene is about to repeat itself—three times.
First – On Sunday evening, April 6th, a 2% crescent moon emerges from the glare of the sun like the wry smile of a Cheshire cat beaming through the tawny-orange sunset. Finding this delicate sliver may require some careful scanning of the western horizon and it would be wise to exit the car (or at least brake) before looking. The next night is easier.
Second – On Monday evening, April 7th, a 6% crescent materializes a little higher in the sky. Set against the cobalt-blue of early evening, the moon reveals its lovely da Vinci glow, a pale impression of the full Moon inside the vivid crescent. Five hundred years ago, Leonardo da Vinci was first to explain this phenomenon: it is Earthshine, the light of our own planet Earth illuminating the Moon's dark terrain. A crescent moon with Earthshine is widely regarded as one of the prettiest sights in the heavens.
But the best is yet to come….
Third – On Tuesday evening, April 8th, a 12% crescent Moon moves into conjunction with the Pleiades. "Into conjunction" is astronomy jargon for "side-by-side." The Moon will be so close to the Pleiades that, to the naked eye, they seem to touch, but that is impossible because the Pleiades are 400 light years away.
Also known as the Seven Sisters, the Pleiades are a cluster of young stars. The brightest seven of these blue-white beauties form a little dipper shape as wide about as the Moon (0.5o). In spite of their great distance, the Pleiades are faintly visible to the naked eye even from urban areas.
On April 8th, the Moon will lead you directly to the Pleiades. Binoculars are recommended: scan around the Moon and you will find not just seven but dozens of sparkling stars, some of them winking in and out behind the mountainous lunar limb. The Moon itself may take your breath away as you sweep your optics across the cratered Earthlit landscape.
As on previous evenings, the best time to look is shortly after sundown, facing west: sky map. The crescent Moon, Earthshine and a star cluster in the same field of view--it doesn't get much better than that.
Epilogue: "I have another car now and I will be heading out Sunday afternoon for an encore performance, not of the wreck, but of the Moon," says Zubenel. He shares his story hoping that it will inspire others to photograph the upcoming display--carefully!