Saturday, March 31, 2012

Strange Phenomena in a Meteorite Crater


Strange phenomena have been happening in Gulong Village, a round pit with a diameter of 1.8 kilometers, since ancient times. It is found that they are due to a meteorite strike in the area.
According to Chinese Science Bulletin, when Gulong villagers get water from wells, there is always a layer of oil on top of the water. In addition, after the black soil from this village is dried, it can burn in fire.
Trees, grasses, crops, and other plants grow very well in the village. Currently, there are 64 families in the village, 30 of which are surnamed Feng. The villagers rarely get sick, so the village is known as a longevity village.
The villagers live a self-sustained life as the rural area is very slow in developing. Without any industry, the environment has little pollution. Because the village is surrounded by mountains, it is very isolated and rarely affected by the outside world. Therefore, these phenomena are likely to be related to the pit itself.
Experts have offered the explanation that tens of thousands of years ago, a large number of plants died and was converted into coal, so the soil became peat. As the soil contains a large amount of coal, it can burn. At the same time, water’s inability to flow through the peat results in oil suspension in the wells.
So how was the pit formed? After three years of investigation, a group of researchers headed by Dr. Chen Ming from the Guangzhou Institute of Geochemistry of the Chinese Academy of Sciences published a paper in 2007 confirming that the Liaoning Xiuyan pit is a meteorite impact crater. After the meteorite strike, the deformation and melting of rock and mineral matter formed the pit.
Chen analyzed the material in the pit and estimated that the meteorite strike happened 50,000 years ago. Water accumulated in the pit to form a lake, and the sediment eventually reached over 100 meters deep. About 39,000 years ago, the lake gradually diminished due to a gap in the east wall of the pit, forming the present bowl-like valley.

Saturday, March 24, 2012

Green Flash


The famed and elusive Green Flash is a rare meteorological phenomenon that occurs at sunset and sunrise. During these times, the sun’s light travels through more of the earth’s atmosphere to reach your eye, creating a prism effect. Yeah, the explanation is definitely more dull than many of the maritime legends surrounding the phenomenon, but consider yourself very lucky if you’re able to witness this event. To increase your chances, watch the sun ( set or rise ) over a long and uninterrupted horizon on a very clear day. The ocean horizon works well for this, as will a prairie, or the horizon line while inside an airplane. 



At sunset or sunrise the top edge of the sun will sometimes be bright green. Often, the green color lasts for a second, thus it is called a green flash. 


It is usually seen over a distant horizon such as an ocean or a prairie. The sky must be clear and free of clouds all the way down to the horizon. There are several different mechanisms that produce green flashes. I'll start with one common misconception that the green flash is due to a color afterimage then move on to a discussion of the atmospheric optics that produces the simplest Green Flash.

The Green Flash is not an afterimage 


People speculated that the green flash was an after image due to the saturation of the red cones in the human retina, or that it was a continued phosphorescence of the atmosphere after the sun had set. However the observation of the green flash at sunrise made both of these ideas impossible.


I was standing on Table Rock in the Linville Gorge Wilderness of North Carolina. It was just before dawn. I studied the eastern horizon and managed to spot a green flash at sunrise! Wow! Then the sun rose as a red ball including a rare naked eye sunspot! What a morning. The drive from Michigan had been well worth it. 
Paul Doherty 1983. 


The making of a simple green flash


Light slows a little bit as it travels through the air of the atmosphere, at sea level the index of refraction of air is 1.0003, which says that light slows by 0.03% compared to its value in a vacuum. Lights from the sun travels through the vacuum of space and then enters the atmosphere of the earth. As the light enters the air it slows and refracts. At sunrise or sunset this means that the lights from the sun bends downward. Thus the image of the sun appears above where the image of the sun would appear if there were no atmosphere. The light is bent downward by 0.5 degree, exactly the diameter of the sun. So the image of the sun we see at sunset is tangent to the image of the sun we would see if there were no atmosphere. Just as the top edge of the sun's atmosphere-less image is touching the horizon, the bottom edge of the sun's image through the atmosphere is touching the horizon. 



The upper circle shows where you see the sun image at sunset due to atmospheric refraction. The lower circle shows where the sun would appear if the atmosphere of the earth were suddenly sucked away. The slowing of light depends on the wavelength of the light, its color. Blue light is closer to the ultraviolet resonances of the molecules and atoms which make up the atmosphere and so it is slowed more than red light. Thus blue light is bent more by the atmosphere than red light. The white image of the sun is actually made up of many different wavelengths of light. These different wavelength images of the sun will be bent by different angles. Thus the red image of the sun will appear below the green image which will appear below the blue image. 


The highest blue image of the sun and lowest red image combine with the central green image to create a white sun with a blue top rim and a red bottom rim. If you look through binoculars at Venus when it is low on the horizon you will see it separated into a spectrum of color blue on top, red at the bottom. When the sun sets all the images of the sun made by wavelengths shorter than green can be blocked by the horizon leaving the top edge of the green image visible. This is one type of green flash. What about the blue light? Well usually the atmosphere scatters blue light to the side more than green light or red light, so that the blue is removed and there is no blue flash. This separation of the sun into its spectrum happens at every sunset but the separation is so small that it normally cannot be seen by unaided eye. It requires optical help from refraction by layers in the atmosphere to make it easily visible. These same layers make mirages.



Mirages and Green Flashes 


Sometimes you will see mirage "puddles" on hot highways. These puddles are called inferior mirages, inferior in the sense of below, they appear below the observer. Inferior mirages are created when light refracts through the hot, low density, low index of refraction air near the earth's surface. More rarely a layer of hot air will be above the ground, above a layer of cold air. This is called a temperature inversion and makes a superior mirage, a mirage that appears above the observer. 
The same temperature gradients that produce mirages can strongly influence the shape of the sun at sunset and the shape and duration of green flashes. 
A sunset through an atmospheric temperature gradient which would produce an inferior mirage causes the bottom of the sun to stretch down toward the horizon and broaden out. This occurs when cold air is over a warm ocean. These flashes are common over tropical oceans. They also happen over temperate oceans when cold air masses move south over warmer water. Most common green flashes are produced by inferior mirage enhancement. The average length of these green flashes in the tropics is 2 seconds. 
A sunset through a superior mirage pulls up the bottom of the sun and often produces a square shaped sun with horizontal fingers of light and dark penetrating the sides. This rarer condition can produce green flashes lasting over 10 seconds. 


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Saturday, March 17, 2012

Ball Lightning

This bizarre electrical phenomenon usually occurs during thunderstorms and lasts for up to thirty seconds. Balls of lightening are said to behave in strange ways, hovering, rolling, hissing and sometimes passing through walls, in a way that seems completely unnatural. As a result, ball lightening has long been associated with aliens and ghosts, and the kind of pseudo-psychic head-cases who believe they can communicate with the other side. Thousands of people throughout history have reported seeing ball lightening, including Benjamin Franklin and my grandmother, but until recently their claims were largely ignored. However, with an increasing amount of photographic and video evidence available, scientists have now begun to take ball lightening seriously and are now attempting to recreate this entirely natural phenomenon within the confines of a laboratory.
Ball lightning is an unexplained atmospheric electrical phenomenon. The term refers to reports of luminous, usually spherical objects which vary from pea-sized to several metres in diameter. It is usually associated with thunderstorms, but lasts considerably longer than the split-second flash of a lightning bolt. Many of the early reports say that the ball eventually explodes, sometimes with fatal consequences, leaving behind the odour of sulfur.
Laboratory experiments have produced effects that are visually similar to reports of ball lightning, but it is presently unknown whether these are actually related to any naturally occurring phenomenon. Scientific data on natural ball lightning are scarce owing to its infrequency and unpredictability. The presumption of its existence is based on reported public sightings, and has therefore produced somewhat inconsistent findings. Given inconsistencies and the lack of reliable data, the true nature of ball lightning is still unknown

Friday, March 9, 2012

Nacreous Clouds




For those of you a bit farther away from the equator, there's still plenty to see in the sky. Nacreous clouds (also called mother-of-pearl clouds) are extremely rare, but unmistakeable in the dark hours before dawn or after sunset. Because of their extremely high altitudes, they reflect sunlight from below the horizon, shining it down brightly, in stark comparison to the regular ol' dark clouds in the troposphere. The lower stratosphere, where nacreous clouds live, is so dry that it often prevents cloud formation, but the extreme cold of polar winters makes this beautiful phenomenon possible. Captured best during winter at high latitudes, nacreous clouds have been spotted in Iceland, Alaska, Northern Canada, and very rarely, farther south in England.
They are filmy sheets slowly curling and uncurling, stretching and contracting in the semi-dark sky. Compared with dark scudding low altitude clouds that might be present, nacreous clouds stand majestically in almost the same place - an indicator of their great height. 
They need the very frigid regions of the lower stratosphere some 15 - 25 km (9 -16 mile) high and well above tropospheric clouds. They are so bright after sunset and before dawn because at those heights they are still sunlit. 

They are seen mostly during winter at high latitudes like Scandinavia, Iceland, Alaska and Northern Canada. Sometimes, however, they occur as far south as England.   They can be less rare downwind of mountain ranges. Elsewhere their appearance is often associated with severe tropospheric winds and storms. 

Nacreous clouds far outshine and have much more vivid colours than ordinary iridescent clouds which are very much poor relations and seen frequently all over the world. 


Saturday, March 3, 2012

Asperatus Clouds


Undulatus asperatus (or alternately, asperatus) is a cloud formation, proposed in 2009 as a separate cloud classification by the founder of the Cloud Appreciation Society. If successful it will be the first cloud formation added since cirrus intortus in 1951 to the International Cloud Atlas of the World Meteorological Organization. The name translates approximately as roughened or agitated waves.

Margaret LeMone, a cloud expert with the National Center for Atmospheric Research has taken photos of asperatus clouds for 30 years, and considers it a likely new cloud type. On June 20, 2006 Jane Wiggins took a picture of asperatus clouds from the window of a downtown office building in Cedar Rapids, Iowa. In March 2009, Chad Hedstroom took a picture of asperatus clouds from his car near Greenville Ave in Dallas, Texas. Soon after taking it, Wiggins sent her Cedar Rapids image to the Cloud Appreciation Society, which displayed it on its image gallery. Since 2006, many similar cloud formations have been contributed to the gallery, and in 2009 Gavin Pretor-Pinney, founder of The Cloud Appreciation Society, began working with the Royal Meteorological Society to promote the cloud type. Wiggins' photograph was posted on the National Geographic website on June 4, 2009. The clouds are most closely related to undulatus clouds. Although they appear dark and storm-like, they tend to dissipate without a storm forming. The ominous-looking clouds have been particularly common in the Plains states of the United States, often during the morning or midday hours following convective thunderstorm activity. As of June 2009 the Royal Meteorological Society is gathering evidence of the type of weather patterns in which undulatus asperatus clouds appear, so as to study how they form and decide whether they are distinct from other undulatus clouds.