Illustration comparing the size of large stars. The small yellow star at the bottom is the Sun, a yellow dwarf main sequence star with a diameter of 1.39 million km (865, 000 miles). Next to it is Sirius A, the brightest star in the night sky, 1.7 times the size of the Sun. These stars pale into insignificance compared to, in order of scale, Arcturus (an orange giant), Aldebaran (another orange giant) and Rigel (a blue super giant). The largest here, Rigel, is 78 times the size of the Sun and 85, 000 times as luminous. If placed at the centre of the Solar System it would reach almost to the orbit of Mercury.