Pi5 Orionis
Pi Orionis (π Ori, π Orionis) is a binary star system in the constellation Orion. It has an apparent visual magnitude of 3.69, which is bright enough to be visible to the naked eye on a clear night. Based upon an annual parallax shift of 2.43 mas, it is around 1,300 light-years distant from the Sun. This is a single-lined spectroscopic binary star system in a circular orbit with an orbital period of 3.7005 days. It is an ellipsoidal variable, which means the orbit is sufficiently close that the shapes of the components are being distorted  by their mutual gravitation. This is causing the visual magnitude of the system to vary regularly by 0.05 over the course of each orbit, as the orientation of the stars change with respect to the Earth. The primary component is a B-type giant star with a stellar classification of B2 III. It is only 16 million years old and spins with a projected rotational velocity of 90 km/s. Pi Orionis has about 12.5 times the mass of the Sun and radiates 11,262 times the solar luminosity from its outer atmosphere at an effective temperature of . Pi5 Orionis Pi