You can get the radius of a spherical circle in radians using
the radius function. The center of the
circle is available with
the operator @@ (Section 5.7).
Example 6.7. Radius of a spherical circle in degrees
sql> SELECT 180.0 * radius( scircle '<(0d,90d),60d>' ) / pi() AS radius;
radius
--------
60
(1 row)