Aurora Borealis - Northern Lights

 









Auroras are natural colored light displays in the sky, which typically occur in the ionoshere and are seen particularly in the polar region. They are the nature's own fireworks, apparently dancing across the dark sky. Aurora Borealis originate from sun. During large explosions and flares, huge quantities of solar particles (plasma clouds) are thrown out of the sun into the deep space. When these solar particles are closing in on earth, they are captured by earth's magnetic field and are guided towards Earth's two magnetic poles ( north pole and south pole). Down towards these magnetic poles, the solar particles are stopped by Earth's atmosphere. There they collide with the atmospheric gases present and the collision energy between the solar particle and the gas molecule is emiited as a photon (light particle). Thus, many such collisions causes an aurora.

The auroral lights' colors are determined by the spectra of gases in the Earth's atmopsphere, and the height at which the most collisions take place. Incoming particles tend to collide with different gases at different heights. Thus the green light occurs at the altitudes of 120 to 180 km, red light occurs at even higher altitudes, while blue and violet occur mostly below 120 km. The most common auroral forms and structures are Homogeneous arc, Arc with ray structure, Homogeneous band, Band with structure, Corona, Curtain etc.

For more information visit: http://www.northern-lights.no/english/what/index.shtml

Lake Assal

 












Lake Assal is a crater lake, located at the southern border of Tadjoura Region. It lies 155 meters below sea level and is the lowest point in Africa. Lake Assal has no outlet, streams flow into the lake and not away from it.

Lake Assal sits at the top of the Great Rift Valley in the Danakil Desert where summer temperatures sometimes reach 52 degree celsius and are accompanied by strong drying winds. It has a high evaporation rate. The air temperature is very high. Strong winds cause further evaporation. All this evaporation leads to an increasing concentration of salt in the water, making the lake a mineralized brine that is the saltiest body of water in the world. The surrounding plain, once the lake floor, is a glistening expanse of salt. During each wet season the lake level rises, and as the water slowly evaporates, another band of salt is laid down on the plain. In the southeastern part of the lake, small fish inhabit the springs, but if they are accidentally carried out into the main part of the lake, they die at once. Transported by the waves, their bodies are thrown onto the plain, rapidly covered with salt and thus preserved.