Determination of the day of the week row C) to find the dominical letter that is E. The letter for September 18 is B, so the day of the week is Thursday. Use 16 (in the Julian century row, column E) and 76 (in row D) to find the dominical letter that is A. February 23 is a "D" day, so the day of the week is Wednesday. In a handwritten note in a collection of astronomical tables, Carl Friedrich Gauss described a method for calculating the day of the week for 1 January in any given year. He never published it. It was finally included in
Ogof Dydd Byraf Over the years this cave had been under threat by the quarry operations, but it is now protected as an SSSI. and owned by North Wales Wildlife Trust Ogof Dydd Byraf Ogof Dydd Byraf is a cave which extends under Esclusham Mountain in north-east Wales from its entrance in the south face of the Minera Limeworks quarry. It was originally discovered and explored in 1964 by the Wrexham Caving Club, before they were merged into the North Wales Caving Club. After a short series of mined passages there is a narrow 10 metre pitch into the main levels consisting of