sao Chức Nữ

Vega — Alpha Lyrae, the leading star of the small constellation Lyra — is a white A-type star whose B–V colour index of −0.001 is almost exactly neutral, long making it a photometric benchmark for stellar colour. It shines at apparent magnitude 0.03 from a distance of 25 light-years, and its absolute magnitude of 0.6 shows an intrinsic brightness only modestly above the value it presents to Earth. Positioned at a northern declination of +38°, Vega climbs high overhead from mid-northern latitudes and forms one apex of the Summer Triangle. Its brilliance and pure white light make it one of the most recognisable stars of the northern summer evening.