Ys
Flight of King Gradlon, by E. V. Luminais, 1884 (Musée des Beaux-Arts, Quimper) Ys (pronounced /ˈiːs/ EESS), also spelled Is or Kêr-Is in Breton, and Ville d'Ys in French (kêr means city in Breton), is a mythical city that was built on the coast of Brittany and later swallowed by the ocean. The legend[edit] Origins[edit] According to some versions of the legend, Ys was built below sea level by Gradlon (Gralon in Breton), King of Cornouaille (Kerne in Breton), upon the request of his daughter Dahut (also called Ahes), who loved the sea. In others, Ys was founded more than 2000 years before Gradlon's reign in a then-dry location off the current coast of the Bay of Douarnenez, but the Breton coast had slowly given way to the sea so that Ys was under it at each high tide when Gradlon's reign began. Fall[edit] Ys was the most beautiful and impressive city in Europe, but quickly became a city of sin under the influence of Dahut. One day, a knight dressed in red came to Ys. A. See also[edit]
Stellar evolution
Representative lifetimes of stars as a function of their masses The life cycle of a Sun-like star. Artist's depiction of the life cycle of a Sun-like star, starting as a main-sequence star at lower left then expanding through the subgiant and giant phases, until its outer envelope is expelled to form a planetary nebula at upper right. Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the age of the universe. The table shows the lifetimes of stars as a function of their masses.[1] All stars are born from collapsing clouds of gas and dust, often called nebulae or molecular clouds. Nuclear fusion powers a star for most of its life. Birth of a star[edit] Schematic of stellar evolution. Protostar[edit] Brown dwarfs and sub-stellar objects[edit]
Nucleosynthesis
Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons, primarily protons and neutrons. The first nuclei were formed about three minutes after the Big Bang, through the process called Big Bang nucleosynthesis. It was then that hydrogen and helium formed that became the content of the first stars, and is responsible for the present hydrogen/helium ratio of the cosmos. With the formation of stars, heavier nuclei were created from hydrogen and helium by stellar nucleosynthesis, a process that continues today. Supernova nucleosynthesis within exploding stars, is responsible for the abundances of elements between magnesium (atomic number 12) and nickel (atomic number 28).[1] Supernova nucleosynthesis is also thought to be responsible for the creation of elements heavier than iron and nickel, in the last few seconds of a type II supernova event. Timeline[edit] History of nucleosynthesis theory[edit] Abundances of the chemical elements in the Solar system.
Beta decay
β− decay in an atomic nucleus (the accompanying antineutrino is omitted). The inset shows beta decay of a free neutron. In both processes, the intermediate emission of a virtual W− boson (which then decays to electron and antineutrino) is not shown. In nuclear physics, beta decay (β decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted from an atomic nucleus. Beta decay is a process which allows the atom to obtain the optimal ratio of protons and neutrons.[1] Beta decay is mediated by the weak force. An example of β− decay is shown when carbon-14 decays into nitrogen-14: 14 6C → 14 7N + e− + ν e Notice how, in electron emission, an electron antineutrino is also emitted. An example of positron (β+ decay) is shown with magnesium-23 decaying into sodium-23: 23 12Mg → 23 11Na + e+ + ν e In contrast to electron emission, positron emission is accompanied by the emission of an electron neutrino. 81 36Kr + e− → 81 35Br + ν e β− decay[edit] β+ decay[edit]
