Angular width of a rainbow arc

This rainbow over the sea seemed very wide so I though to measure it with my little finger. If my finger is 1 degree wide, then it looks as though the width is about 1.5 degrees. I need to go away and do the maths for the refraction of the red and of the violet and find the difference. Newton was apparently the first to do this getting about 1.5 degrees but realised that the rays from the Sun came parallel from a point source not from a disc so it is really just a fraction over 2 degrees. http://www.datalyse.dk/Rainbow/history.htm