One arcsecond, or second of arc, is 1/3600th of a degree. There are 60 arcseconds in one arcminute, 60 arcminutes in one degree, and 360 degrees in a full circle. One thousandth of an arcsecond = 1 milliarcsecond.
One degree is 1/360 of a circle.
The radian is one of two supplementary (dimensionless) units in the SI system of units (the other being the steradian). The radian is a unit of plane angle. There are 2π radians in a complete circle. One radian = 180/π degrees, or approximately 57.296°.
The steradian (sr) is one of two supplementary (dimensionless) units in the SI system of units (the other being the radian). The steradian is a unit of solid angle. It is defined as the solid central angle of a sphere which encloses a surface on the sphere equal to the square of the sphere's radius.