P Cygni

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**P Cygni**
Star	listing of stars

P Cygni is a variable star in the constellation Cygnus.

Until the 17th century it was unknown, but then suddenly brightened to 3rd magnitude. It briefly disappeared and returned, and today has a magnitude of 4.82.

P Cygni is 5000 to 6000 light years from Earth, a supergiant (hypergiant?) of spectral type B2 Ia. It is difficult to determine its exact distance, since the parallax is very small.

P Cygni gives its name to a type of spectroscopic feature called a P Cygni profile, where the presence of both absorption and emission in the line profile indicate the existence of a gaseous envelope expanding away from the star. These profiles are useful in the study of stellar winds in many types of stars.