light curve for R Doradus, adapted from Bedding
et al. (1998) The
visible magnitude of R Doradus varies between 4.8 and 6.3, which means it is usually visible to the
naked eye, but in the
infrared it is one of the brightest stars in the sky. With a near-infrared
J band magnitude of −2.65, only
Betelgeuse and
Antares at −2.9 and −2.73 (respectively) are brighter. In the infrared
K band, it is sometimes the brightest star in the sky, although usually
Betelgeuse is brighter. It is classified as a
semiregular variable star of type SRb, indicating giants with slow poorly defined variations, often alternating between periodic and irregular brightness changes. Some studies show it alternating between periods of about 175 and 332 days, and a period of 117.3 days has also been identified. It has been likened to a
Mira variable when its variations are relatively regular, although its amplitude of only 1.5 magnitudes is smaller than Mira variables. The star was discovered to be variable in 1874 by
Benjamin Gould, and received the
variable-star designation R Doradus. == Angular diameter ==