StarWatch for the greater Lehigh Valley



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[Moon Phases]
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733    SEPTEMBER 5, 2010:   Seasonal Lag Makes Summer a Drag
Right now the thermometer outside my window reads 94 degrees F. For the most part here on the East Coast, it’s been a miserable summer, filled with hot humid days and warm muggy nights. Shortly, Hurricane Earl is forecast to skim past the Mid-Atlantic States. When it moves northeast of us, its counterclockwise circulation should drive cooler air from the north into our region. Make no mistake; cooler weather is on its way. Summer’s heat will gradually give way to crisp Canadian cold fronts that will herald fall. All of this is a function of Earth’s axial tilt which increases and decreases the amount of energy we receive from the sun. Now the sun is on the downslide, racing southward, rising later each morning and setting earlier each evening. Since the June 21, summer solstice, and through September 8, a length of time equal to 80 days, people living at 40 degrees N latitude have lost 128 minutes of daylight. During the next 28 days, starting on September 9 and centered on the autumnal equinox of September 22, we will lose an additional 74 minutes of sunlight. Still, temperatures will be mostly pleasant, with the occasional warm, dreamy Indian summer day. The cooling and heating of the Earth for mid-latitude climes is not in synchronization with the seasons. The hottest days of the year from a statistical standpoint occur in late July, while the traditionally coldest time of the year happens near the end of January. Climatic temperatures depend upon the daytime energy absorbed from the sun and the nighttime radiation of heat lost back into space. Although we receive the most solar energy on June 21, the Earth’s balance between energy gained and energy lost does not happen until about a month after the solstices. So yes, hurricane season won’t end until December 1, and we are not yet free from the Dog Days of summer, but we are moving in the correct direction.

734    SEPTEMBER 12, 2010:   Meteorites: Window to Our Past
I have a fascination with meteorites. They are natural space debris, mostly from the asteroid belt, that makes it down to the Earth’s surface. When you hold a meteorite in your hand, you are making contact with something that was formed during the very earliest days of our solar system, in some cases before there was even an Earth. The earliest terrestrial rocks, found in southwestern Greenland, are 4.1-4.3 billion years old. Meteorites consistently date to 4.5 billion years, indicating when these materials first crystallized. Although the classification of meteorites is complex, they fall into three broad groupings: irons, stony-irons, and stones. Respectively, they account for four, one, and 95 percent of all witnessed falls. What they signify is how objects between Mars and Jupiter accreted (came together). As the solar nebula cooled, grains of silica and metals bumped into one another to form larger and larger bodies, many of which became so huge that they compressed, heated, and melted to form mini-planets. The denser materials like iron settled to form the cores of these bodies. Rocky materials (silicates) rose to the surface. At the interface between the core and mantle, small amounts of iron and rock mixed to become the stony-irons. Some objects were too small to undergo this differentiation process; the metals still remained mixed with the silica, in many cases retaining the original clumps of matter, the chondrules, that formed them in the first place. Stony meteorites are divided into chondrites and achondrites (without chondrules) with varying amounts of metals found within the silica. When Jupiter’s gravity began changing the orbits of the asteroids, collisions resulted. Most of the larger and smaller bodies were broken up, creating our present meteorite classification system, and giving us a window to glimpse the primordial soup that eventually became our solar system.

735    SEPTEMBER 19, 2010:   In Search of Libyan Desert Glass
During the past several weeks I have been researching meteorites, in preparation for a talk to the PA Earth Sciences Association. Not all space rocks come from outer space. It is currently thought that many meteorites fragment and explode before hitting the Earth, sending a shower of smaller stones and an intense, hot shock front that melts the rock at ground zero. Irgizite glass found in the Zhamanshin Crater in Kazakhstan and Libyan Desert glass may be prime examples of this process. It is the Libyan Desert Glass that intrigues me the most. It is simply melted sand. So why is it priced normally at three dollar per gram? Boot up your computer and Google Egypt. Then go to the SW corner of the country where Libyan Glass can be found. Yes, it comes from Egypt. It is at the intersection of Libya to the west, and the Sudan to the south. Look around for roads. There are none. It is about as far away from civilization as you can possibly get. The closest roads on the Egyptian side, where the approach is made, are 600 miles away. That’s from the Jersey Shore to western Ohio. When you go in search of Libyan Glass, there is no margin for error. No one will come and rescue you if you have a flat or get stuck in the sand or run out of anything necessary to return back to humanity. The Land Rovers that make the trip carry 150 gallons of fuel, 150 gallons of water, and all of the spare parts necessary to fix the vehicle if the unimaginable happens. All driving stops around noontime because shadows are so scarce that it is impossible to see if you’d be driving off a cliff. In the shifting dunes blown by the endless, hot wind, Libyan Glass glints with an eerie greenish hue near sundown and sunup. You might be lucky and collect a hundred pounds or more on your trip, and then, you may return empty-handed. I now feel a little guilty at having chewed down a dealer to two dollars a gram to acquire my sample.

[Libyan Desert Glass]

736    SEPTEMBER 26, 2010:   Tektites: A Sure Bet
I have been talking about “rocks from heaven,” meteorites, for the past two weeks. They can be very expensive, even the heat-generated glass created from the atmospheric explosions of meteoroids in the atmosphere. However, there is a “space rock” that everyone can afford, and you will almost always find them at local rock shows. They are called tektites, and although they are not the rocks from heaven themselves, they are the result of large meteorite hits on the Earth’s surface. When a meteorite impacts with its space velocity intact, its speed can change from 10 to 15 miles per second to zero in an instant. This releases a tremendous amount of heat energy, vaporizing the meteorite and the surface rock at ground zero, and in some instances, as the crater is being formed, ejecting large quantities of melted glass (rock) hundreds of miles away. The liquefied rock cools in flight, forming spherically shaped objects, dumbbells, rods, boomerangs, ovals, splashes, and in their most exotic state, button type shapes. You can easily pay $2,000 for a perfect, button tektite from Tasmania (Australia) and hundreds of dollars for a translucent green Moldavite from the Czech Republic. However, tektites from the Australasian part of the world (except for buttons) are generally very reasonably priced, several to 10 dollars per item. The most common are Thailandites from Thailand, usually in the form of shiny, spheres an inch or two in diameter. Years ago, you could find dumbbells, elongated specimens, and teardrop-shaped Thailandites. Close examination would reveal flow lines created as the glass moved rapidly through the air as it was solidifying. Today, these seem to be segregated from the more common spheres and sold at a higher price. Australasian tektites were formed about 700,000 years ago from some yet-to-be-discovered impact site. Good hunting!

[World Distrbution of Tektites]

[September Star Map]

[September Moon Phase Calendar]