are expected to explode as supernovae. Like most cool supergiants, Antares's size has much uncertainty due to the tenuous and translucent nature of the extended outer regions of the star. Defining an effective temperature is difficult due to spectral lines being generated at different depths in the atmosphere, and linear measurements produce different results depending on the wavelength observed. In addition, Antares appears to pulsate, varying its radius by 19%. It also varies in temperature by 150 K, lagging 70 days behind radial velocity changes which are likely to be caused by the pulsations. The diameter of Antares can be measured most accurately using interferometry or observing lunar occultations events. An apparent diameter from occultations 41.3 ± 0.1 milliarcseconds has been published. Interferometry allows synthesis of a view of the stellar disc, which is then represented as a limb-darkened disk surrounded by an extended atmosphere. The diameter of the limb-darkened disk was measured as in 2009 and in 2010. The linear radius of the star can be calculated from its angular diameter and distance. However, the distance to Antares is not known with the same accuracy as modern measurements of its diameter. The Hipparcos satellite's trigonometric parallax of leads to a radius of about . Older radii estimates exceeding were derived from older measurements of the diameter, but those measurements are likely to have been affected by asymmetry of the atmosphere and the narrow range of infrared wavelengths observed; Antares has an extended shell which radiates strongly at those particular wavelengths. Despite its large size compared to the Sun, Antares is dwarfed by even larger red supergiants, such as VY Canis Majoris or VV Cephei A and Mu Cephei. Antares, like the similarly sized red supergiant Betelgeuse in the constellation Orion, will almost certainly explode as a supernova, probably in million years. For a few months, the Antares supernova could be as bright as the full moon and be visible in daytime. Antares B Antares B is a magnitude 5.5 blue-white main-sequence star of spectral type B2.5V; it also has numerous unusual spectral lines suggesting it has been polluted by matter ejected by Antares. It is assumed to be a relatively normal early-B main sequence star with a mass around , a temperature around , and a radius of about . Antares B is normally difficult to see in small telescopes due to glare from Antares, but can sometimes be