Astronomy can also provide clues for dates. The best known of these is the Sothic cycle. A study of this led Richard A. Parker to argue that the dates of the Twelfth dynasty could be fixed exactly. New research does not agree with some of the information used in to work out dates this way For example, Donald B. Redford, in attempting to fix the date of the end of the Eighteenth dynasty, did not use the Sothic evidence. Instead he used, links between Egypt and Assyria (by way of the Hittites), and help from astronomical observations.