R☉ - nominal solar radius

6.95700e8 m

A unit of distance used to express the size of stars in astronomy. Defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3. The nominal values were adopted to help astronomers avoid confusion when quoting stellar radii in units of the Sun's radius, even when future observations will likely refine the Sun's actual photospheric radius (which is currently only known to about the +-100-200 km accuracy).