code: def add_offset_radec(ra_deg, dec_deg, delta_deg_ra, delta_deg_dec):
      
      # To radians
      x = math.radians(delta_deg_ra)
      y = math.radians(delta_deg_dec)
      raz = math.radians(ra_deg)
      decz = math.radians(dec_deg)
  
      sdecz = math.sin(decz)
      cdecz = math.cos(decz)
  
      d = cdecz - y * sdecz
  
      ra2 = math.atan2(x, d) + raz
      # Normalize ra into the range 0 to 2*pi
      twopi = math.pi * 2
      ra2 = math.fmod(ra2, twopi)
      if ra2 < 0.0:
          ra2 += twopi
      dec2 = math.atan2(sdecz + y * cdecz, math.sqrt(x * x + d * d))
  
      # back to degrees
      ra2_deg = math.degrees(ra2)
      dec2_deg = math.degrees(dec2)
  
      return (ra2_deg, dec2_deg)
docs: Algorithm to compute RA/Dec from RA/Dec base position plus tangent
      plane offsets.