R_☉

• The R is not always italic.

• R (radius) and subindex ☉ (sun).

R_☉

1. (astronomy) solar radius: a unit of distance, equal to the radius of the Sun: 7×10⁸ m or 110 R_🜨.

   The inner edge of the [circumbinary] disc is at 317 R_☉, well outside the inner binary orbit.

2. (sum of parts) The radius of the Sun specifically

• R_☉ may be distinguished from r_☉, the latter not a unit of measurement but meaning radial distance from the sun (heliocentric distance). Unlike the unit R_☉, r_☉ is used specifically for our sun; for another star, r_＊ or r_✶ is likely to be used.