A planetary nebula (PN, plural PNe) is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives.The term "planetary nebula" is a misnomer because they are unrelated to planets. The term originates from the planet-like round shape of these nebulae observed by astronomers through early telescopes. The first usage may have occurred during the 1780s with the English astronomer William Herschel who described these nebulae as resembling planets; however, as early as January 1779, the French astronomer Antoine Darquier de Pellepoix described in his observations of the Ring Nebula, "very dim but perfectly outlined; it is as large as Jupiter and resembles a fading planet". Though the modern interpretation is different, the old term is still used. All planetary nebulae form at the end of the life of a star of intermediate mass, about 1-8 solar masses. It is expected that the Sun will form a planetary nebula at the end of its life cycle. They are relatively short-lived phenomena, lasting perhaps a few tens of millennia, compared to considerably longer phases of stellar evolution. Once...

A planetary nebula (PN, plural PNe) is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives.The term "planetary nebula" is a misnomer because they are unrelated to planets. The term originates from the planet-like round shape of these nebulae observed by astronomers through early telescopes. The first usage may have occurred during the 1780s with the English astronomer William Herschel who described these nebulae as resembling planets; however, as early as January 1779, the French astronomer Antoine Darquier de Pellepoix described in his observations of the Ring Nebula, "very dim but perfectly outlined; it is as large as Jupiter and resembles a fading planet". Though the modern interpretation is different, the old term is still used. All planetary nebulae form at the end of the life of a star of intermediate mass, about 1-8 solar masses. It is expected that the Sun will form a planetary nebula at the end of its life cycle. They are relatively short-lived phenomena, lasting perhaps a few tens of millennia, compared to considerably longer phases of stellar evolution. Once...

In the field of military theory, the operational level of war (also called operational art, as derived from Russian: оперативное искусство, or operational warfare) represents the level of command that connects the details of tactics with the goals of strategy.In Joint U.S. military doctrine, operational art is "the cognitive approach by commanders and staffs—supported by their skill, knowledge, experience, creativity, and judgment—to develop strategies, campaigns, and operations to organize and employ military forces by integrating ends, ways, and means." It correlates political needs and military power. Operational art is defined by its military-political scope, not by force size, scale of operations or degree of effort. Likewise, operational art provides theory and skills, and the operational level permits doctrinal structure and process.The operational level of war is concerned with four essential elements: time, space, means, and purpose. Through means such as directing troops and allocating (limited) resources (among others), operational art aims to achieve political goals by producing an optimal (or at least near-optimal...

A pan flute (also known as panpipes or syrinx) is a musical instrument based on the principle of the closed tube, consisting of multiple pipes of gradually increasing length (and occasionally girth). Multiple varieties of pan flutes have been popular as folk instruments. The pipes are typically made from bamboo, giant cane, or local reeds. Other materials include wood, plastic, metal and ivory. Name The pan flute is named after Pan, the Greek god of nature and shepherds, often depicted with such an instrument. The pan flute has become widely associated with the character Peter Pan created by Sir James Matthew Barrie, whose name was inspired by the god Pan.In Greek mythology, Syrinx (Σύριγξ) was a forest nymph. In her attempt to escape the affection of god Pan (a creature half goat and half man), she was transformed into a water-reed or calamos (cane-reed). Then, Pan cut several reeds, placed them in parallel one next to the other, and bound them together to make a melodic musical instrument. Ancient Greeks called this instrument Syrinx, in honour of the Muse, and Pandean, or Pan-pipes and Pan-flute, after...

Culture of fear (or climate of fear) is the concept that people may incite fear in the general public to achieve political or workplace goals through emotional bias. It was developed as a sociological framework by Frank Furedi and has been more recently popularized by the American sociologist Barry Glassner. In politics Nazi German politician Hermann Göring explained how people can be made fearful and to support a war they would otherwise oppose: The people don't want war, but they can always be brought to the bidding of the leaders. This is easy. All you have to do is tell them they are being attacked, and denounce the pacifists for lack of patriotism and for exposing the country to danger. It works the same in every country. In her book State and Opposition in Military Brazil, Maria Helena Moreira Alves found a "culture of fear" was implemented as part of political repression since 1964. She used the term to describe methods implemented...

In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and multi-tasking.Its emergence as the prominent model of computing in the 1970s represented a major technological shift in the history of computing. By allowing many users to interact concurrently with a single computer, time-sharing dramatically lowered the cost of providing computing capability, made it possible for individuals and organizations to use a computer without owning one, and promoted the interactive use of computers and the development of new interactive applications. History Batch processing The earliest computers were extremely expensive devices, and very slow in comparison to later models. Machines were typically dedicated to a particular set of tasks and operated by control panels, the operator manually entering small programs via switches in order to load and run a series of programs. These programs might take hours to run. As computers grew in speed...