An afterglow is a broad, high arch occasionally seen in the sky. It is a white light appearing during the darker half of thetwilight. It is caused by fine particles of dust suspended in the upper atmosphere.
Occurrence of an afterglow
Gamma-rays bursts,which are flashes of the gamma rays, are associated with explosions which are highly energetic. Thebursts occur initially and are followed by an afterglow emitted at longer wavelengths. Models that explain the origin of gamma rays have shown that the initial burst is gradually followed by fading emissions.The emissions occur due to collisions between the interstellar gases and the burst eject.
The fading emission is called the afterglow. It is difficult to observe the position of a burst and therefore early searches for afterglows were unsuccessful. A satellite in 1997 was able to detect a gamma ray burst and a fading x-ray emission was observed, when a camera was pointed towards the origin of the burst. Once the gamma ray burstsfaded, deep imaging could “identify a faint, distant host galaxy at the location of the burst as pinpointed by the optical afterglow” (Vedrenne, 2001).
There are long term effects after exposure to gamma ray bursts in the earth’s atmosphere. The gamma ray energy causes “chemical reactions involving oxygen and nitrogen which form nitrogen dioxide gas”. The gas causes a photochemical smog which covers the sky making dark. It further prevents sunlight from reaching the earth’s surface, therefore causing a cosmic winter event.Further,it depletes the ozone layer and consequently the earth becomes vulnerable to any sorts of radiation.
An airglow is a faint photochemical glow in the higher parts of the atmosphere. It is caused by collision of x-rays and charged particles from the sun, with molecules and atoms. It occurs especially in low altitudes. The airglow hasa green oxygen line,which makes up the major subject of study to understand the appearance and occurrence of airglows.
Cause and occurrence of an airglow
The oxygen line appearing in an airglow has been studied by scientists and spectroscopists for decades. They have come up with two distinct ways of approaching the phenomenon;the electron excitation hypothesis and the photochemical excitation theory (Bates and Chamberlain, 1996).
According to photochemical excitation, radiation in the airglow is basically, the photochemical release of oxygen dissociation energy stored in the lower regions of the thermosphere. It is an established fact that the transition of oxygen from molecular to atomic states occurs at the same level (Khomic,2010).
When energy is deposited in the air, the molecules become excited and as a result, gases like oxygen and nitrogen react to form molecules. The molecules react with other molecules forming ozone. Presence of air vapor, which is characterized emission of hydrogen makes the plasma react with other chemicals in the air. As a result, their collision with x-rays leads to occurrence of an airglow.
An alpenglow is easily observed when the sun is just below the horizon. Light from the sun lacks a direct path to reach the earth’s surface, so it instead reflects water, snow or ice particles. In this scenario, a normal sunrise or sunset is separated from the alpenglow. In the case where there are no mountains, the aerosols of the sky are illuminated instead.
To define an alpenglow, the scientists agree that it is a diffused and indirect illumination, which occurs through refraction as a result of moisture and pollutants in the atmosphere. It often occurs before sunrise or just after sunset. It makes the sky look redand it eventually glows. It only lasts for a short period in the lowlands therefore not often observed.
The red light waves are usually the longest in the visible spectrum of the electromagnetic energy and they are also the slowest in motion. As light travels through the atmosphere, the blue color is absorbed. The slower red color is not highly absorbed and it therefore appears in the electromagnetic spectrum. As the sun sets or rises, a gradation of color rise in the eastern sky is observed which is orange-red or purple.
The color transition is actually the horizontal view of the line between day and night. The orange-red light is the sunset light that goes on rising in the sky as the sun sets. The purple light is the earth’s shadow rising to the sky. Mountains obtain the red light since they are higher and can also light the clouds after sunset (Dickson,1988).
Blue flashes form in a similar way as green flashes and are more difficult to see because they blend into the surrounding sky, which is also blue. It results from spectral emission of excited molecules in the air especially with oxygen and nitrogen. The molecules fall back to unionized states and consequently produce a blue light. The light is often associated with Cherenkov radiation, due to its similarity in color. It is usually followed by a heat wave which is a physical effect due to heating by the energy emitted during the event.
Cause and occurrence of a blue flash
“Air is a refractive medium therefore it bends light. The bending progressively becomes stronger as it light approaches the surface of the earth and as air density increases. At sunset, the sun’s image is elevated to about half a degree above its normal height. Moreover, air, which is dispersive, bends light of different frequencies and amounts” (Vedrenne, 2001).
By viewing thesunsetusing a telescope, a blue disk is observed to be higher than the red disk. Since the resolution of a naked eye is only 50cm at a distance of 1km, this explains why the blue fringe is not observed at the highest part of the sun.
At sunrise and sunset, the sun’s rays go much longer distance through the atmosphere. The light which reaches the earthalready has a big portion of the blue color removed, making the sun appear red.Due to the scarcity of blue light, there is a shift of stimulus towards yellow that makes the yellow color appear more than the blue one.
As it is known that when eyes see a small patch of light, the smaller patch is perceived to shift in color, in the direction of the color complementary to that of the larger patch (Vedrenne, 2001).Therefore, with the large sky expanded in a greenish yellow patch, it appears more biased to be blue green and eventually it is observed as green. A blue flash appears in case the atmosphere is absolutely clear, and so the “scattering does not deplete much of the blue component” (Vedrenne, 2001).
The green flash is more elusive because its index of refraction get higher without any interruption when coming to the earth’s surface. “The gradient of the index of refraction should be higher in order to accelerate dispersion of colors”(Vedrenne, 2001). Due to turbulences in the atmosphere, like anomalies in temperature, abnormal refraction is caused that can usually produce a confused gradient of colors.
An earthquake light is an abnormal luminous phenomenon that appears in the sky or close to regions of tectonic stress, seismic activity and or volcanicity.It happens right before or during an earthquake. “Like many light appearances in the sky, earthquake lights are a mystery”. No one can distinctively tell why or how they come about. The lights appear multicoloredand are usually brighter during the incident than they before or after.
The lights exist for quite sometime unlike in other phenomenawhere there is a possibility of mistaken identity. Research accounts that the lights were absent until 1930, where at the time an earthquake occurred in Japan (Freund, 2004) .It has been suggested that the lights appear due to gases released during the earthquakes or due to its forces.
Occurrence of earthquake lights
Proposed mechanismsexplaining occurrence of earthquake lights include piezoelectricity, solo luminescence, and heat due to friction, exoelectron emissions and electro kinetics. Piezoelectric activity is caused by stress within the fault zone, ionization from radon, triboluminesccence from rocks, which rub against each other and the release of methane gas.
Methane gas explains the occurrence of light both before and even during an earthquake. Portions of trapped gas would be expected to seep from the ground and possibly ignite due to friction in the moving rock. However, big portions of methane gas are not distributed widely enough in all the regions that earthquake lights are reported to occur. Radon ionization takes a vital and crucial role in pre-seismic and paranormal activities too but it is not viewed as a model.
This is because there are no sufficient random clouds produced, to provide enough ionization for visible glows. Earthquake lights may be considered as physical phenomenon or of a spiritual nature according to the varied descriptions of light occurrence. Taking an example of a country like Japan, where the lights are experienced frequently; there are entities,which associate the lights occurrence to ghosts.(Ahrens&Donald, 2009).
These are natural displays of light which appear in the skies especially at high attitudes. They are mainly caused by collisions of energetically ionized molecules, with atoms in the higher altitudes of the atmosphere. They have a curtain like shape at their lower edges. The lights occur in the ring-shaped regions around the southern and northern poles. Alaska provides a nice view for these lights especially in the Fairbanks.
Occurrence- Aurora borealis and australis
The aurora borealis are lights occurring in the northern latitudes and are therefore named after the goddess of dawn, while the australis are lights seen in the southern pole. Both of lights are caused by very swift moving electrons within atoms in the earth’s upper atmospheres, especially oxygen and nitrogen. As this occurs, the atoms are ionized and as they return to normality, they produce excess energy which is in the form of visible electrons. The fast moving electrons originate from the sun.
Charged particles are constantly striking the earth and are therefore “deflected by the earth’s magnetic field” (Ahrens&Donald, 2009). They movealong the field lines, and some of them ending up interacting with the magnetic field lines. As they cut across the field, they produce a current which allows production of a large amount of power.
This current makes a fairly unstable condition in the magnetosphere. With time, some of this current is discharged causing electrons in the magnetosphere move down towards the poles and through the earth’s upper atmosphere. As it reaches the atmosphere, it bombards basically with oxygen and nitrogen. While this occurs, the atoms jump to high energy orbitals.
This state is fairly unstable for these atoms and this makes them return faster to their normal orbitals. Consequently, they must release the excess energy they had stored up from this collision,inform of a photon.As a good number of these atoms go from the higher orbital energetic state to the lower orbital energetic state, they produce enough light which is viewable even to the naked eye by peoplestanding in strategic locations on the earth.
The meteorological studies affect all beings on the planet. The various phenomena are significant in prediction of weather patterns and storms; this is in turn useful in determining issues and or factors like the ozone layer deterioration and our depleting water supply. They orient us on how to work in harmony with the surrounding and make us informed on the mechanisms behind occurrence of natural phenomena.
Ahrens, C. &Donald, G (2009). Meteorology today. Belmont: Brooks Publishers.
Bates, A. & Chamberlain, H. (1996). Magnetic changes associated with crustal activity, New York:Sons Ltd.
Chapman, A. A. (2001). Astronomy.New York: Walters’s Ltd.
Dickson, T. (1988).Exploring the sky by day: The Equinox Guide to weather and atmosphere. Toronto: Firefly Books Ltd.
Freund, F.(2004).Charges in the electrical conductivity of igneous rocks, the generation of ground currents.New York: Penguin Publishers Ltd.
Khomic, V. (2010).Airglow as an indicator of upper atmospheric structure and dynamics. Moscow. Springer Publishers Ltd.
Vedrenne, A. (2001).The blue flash. Toronto: New books production.