Thanks for replies folks.
It was in fact the Air New Zealand rescue of the Cessna over the Pacific that prompted my question.
Using only rough sun sightings and headings the AirNz Captain was able to estimate the Cessna to be around 210nm to his south west. Figuring out the approx direction is easy enough but how he came up with a distance was not clear to me. He estimated the difference in sun angle above the horizon to be around 4°. 4x60=240, corrected for latitude = around 210nm. Can I make a direct comparison like that between angles and distance ?
The rest of the story of him using vhf radio range to figure out position is well documented.