R Doradus

R Doradus (also called HD 29712) is the name of a red giant Mira variable star in the far-southern constellation Dorado, although visually it appears more closely associated with the constellation Reticulum. Its distance from Earth is 178 ± 10 light-years (55 ± 3.1 parsecs). Having a uniform disk diameter of 0.057 ± 0.005 arcsec, and given its distance, it is currently believed to be the star with the second largest apparent size as viewed from Earth (right after the Sun). The estimated diameter of R Doradus is 515 ± 70 million km (3.46 AU) or 370 ± 50 times the diameter of the Sun. If placed at the centre of the Solar System, the orbit of Mars and most of the main asteroid belt would be contained within the star.

The visible magnitude of R Doradus varies between 4.8 and 6.6, which makes it usually just visible to the naked eye, but in the infrared it is one of the brightest stars in the sky and its total luminosity is 6500 ± 1400 times that of the Sun. With a near-infrared J band magnitude of -2.6, only Betelgeuse at -2.9 is brighter.