आर्द्रा तारा

Deep red in colour, Betelgeuse registers a B–V index of 1.5, one of the reddest values among the bright stars and the visual signature of its M-type classification. It is Alpha Orionis, the star marking Orion's shoulder, and glows at apparent magnitude 0.45 from a distance of some 498 light-years. An absolute magnitude of −5.47 reveals an intrinsic luminosity vastly exceeding the Sun's, which is why the star stays conspicuous across such a span of space. Sitting almost on the celestial equator at declination +7°, Betelgeuse is visible worldwide and, with blue-white Rigel opposite, gives Orion its distinctive colour contrast of a fiery shoulder set against a brilliant foot.