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Contrails (/ˈkɒntreɪlz/; short for "condensation trails") or vapour trails are long thin artificial clouds that sometimes form behind aircraft. Their formation is most often triggered by the water vapour in the exhaust of aircraft engines, but can also be triggered by the changes in air pressure in wingtip vortices or in the air over the entire wing surface. Like all clouds, contrails are made of water, in the form of a suspension of billions of liquid droplets or ice crystals...

A POTD is an acronym for "Photo of the Day", "Picture of the Day", "Post of the Day" or "Poll of the Day". It is a term most commonly used by online digital photography communities as an honor to outstanding photos that are selected daily from among that community's membership. They can either be tagged as POTD or displayed in a special page on that site...

Katy Perry (born Katheryn Elizabeth Hudson; October 25, 1984) is an American singer-songwriter and actress. Born in Santa Barbara, California, and raised by Christian pastor parents, Perry grew up listening to only gospel music and sang in her local church as a child. After earning a GED during her freshman year of high school, she began to pursue a career in music...

Bears are mammals of the family Ursidae. Bears are classified as caniforms, or doglike carnivorans, with the pinnipeds being their closest living relatives. Although there are only eight living species of bear, they are widespread, appearing in a wide variety of habitats throughout the Northern Hemisphere and partially in the Southern Hemisphere. Bears are found in the continents of North America, South America, Europe, and Asia...