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Disk and disc have very similar pronounciation, but they are very different: 2 alternative spelling for things that are generally thing and circular geometry. For the most part the words “disc” and “disk” can be used interchangeably to describe these flat, rounded objects. The terms and the objects appear in fields such as computers, media, science, anatomy and automotive mechanics. Some of these fields primarily use one spelling, others use both, depending on the specific object. In many fields the spellings can be used interchangeably, but generally in computer technology the word disk refers to the magnetic storage (hard disks, floppy disks or diskettes) while disc refers to optical storage (compact discs or CDs, digital versatile discs or DVDs).
In computers and media these 2 words refer to storage devices for data, music and videos. You can store all kind of files on them, but the difference in their structure give you different ways to write, organize and read the data from them.
Sky glow is the illumination of the night sky (partially or completely). Its most common cause is the artificial light of the cities which accumulates into a vast glow that can be seen from many kilometers away in any direction. Sky glow from the artificial lights is common throughout the world, it can be observed as a glowing dome of the populated area.
Other causes include natural sources as the starlight and airglow emitted in the upper utmosphere. Sky glow can also be caused by natural occurences like the meteorits or comets entering in the atmoshpere. One famous event happened in 1908 in Tunguska when an meteoroid spanning a few meters in radius exploded some kilometers above the Podkamennaya Tunguska River in the Krasnoyarsk Krai region of Russia. The light emitted from the Tunguska explosion was so great that it created skyglow as far away as England, the population over there experienced intermittent “bright nights” (a term that is now synonymous with sky glow) for several weeks.