Headius has now fixed to some extent refinements in JRuby, thus it should be possible to use refinements to provide :radians and :degrees methods to Numeric, rather than monkey patching global space.

module SuperNumeric
  refine Numeric do
    def degrees
      self * 57.29577951308232
    end

    def radians
      self * 0.017453292519943295
    end
  end
end

using SuperNumeric

puts 45.radians
puts 0.7853981634.degrees