The postal authorities of Denmark and China have jointly issued a set of stamps commemorating famous astronomers from both countries, and a launch ceremony was held here Wednesday. The series of two stamps, called Ancient Astronomical Instruments, feature the Abridged Armilla of the 13th century Chinese astronomer Guo Shoujing, and the armillary sphere of his 16th century Danish counterpart Tycho Brahe. \"It was important for both postal authorities to find a cultural theme that we could collaborate on,\" said Lene Reipuert, Manager of Stamps at Post Danmark. \"We came to agree on astronomy because we have this history of astronomy, in Denmark with Tycho Brahe, and with the tradition of astronomy going much further back in China,\" she told Xinhua. According to Post Denmark, it was the first time the two countries\' postal authorities collaborated on design and issue of such philatelic products. Reipuert presented a commemorative edition of the stamps to Han Xiaodong, Charge D\'Affaires at the Chinese Embassy in Denmark, at the ceremony, which took place at Tycho Brahe planetarium in Copenhagen and was attended by around 200 people. Han congratulated Post Denmark on the joint release of the stamps, saying the collaboration reflected the warm relations between the two countries for over 60 years. The stamps series was previously launched at a joint ceremony in Nanjing, China, on Dec. 10, 2011. \"The next step is, we start the sale of these stamps. They are also made for franking, so they will be on a lot of letters in Denmark and mailed internally here,\" Reipuert said. Stamp collectors and customers can buy the stamps at China Post outlets, and at Post Denmark shops and its website. Cooperation between the two postal authorities began in December 2009. In April 2010, they established a school in Beijing to train Chinese stamp designers, and boost their skills in steel engraving for stamps. The astronomy series is a product of this collaboration. The stamps are designed by Cui Yanwei and Per Ingemann, and are engraved by Martin Morck, an engraver with over 35 years\' experience. \"Hand engraving ... is an old technique developed in the 14th century. You engrave by cutting the picture into a steel plate. This is what China Post wants to re-establish in China,\" Morck, who teaches engraving at the Beijing school, told Xinhua. The Danish stamps in the series are hand engraved, but the Chinese stamps are laser engraved in a special way, so that they look as if they are hand engraved, he added. It takes \"between two to four weeks to engrave a stamp\" using either process, and that is preceded by a long period of designing and drawing, Morck said. While astronomers Guo and Brahe built remarkably similar astronomical instruments, they were separated by three centuries and lived in very different cultures. \"There is no causal connection between them,\" said Helge Kragh, Professor in History of Science at Aarhus University. \"But there is a similarity in their construction elements (because) if you wanted to study the heavens scientifically, you had to make such instruments,\" he told Xinhua. Now, practical collaboration between Danish and Chinese postal authorities means they are clearly influencing each other\'s work. \"We learned a lot about developing new philatelic products through our cooperation with China Post. (The Chinese) designers are very innovative people, and like to push us a little further,\" Reipuert said. Post Denmark and China Post are now looking ahead to their next venture, namely a set of stamps commemorating Danish author H.C. Andersen. They are designed by Chinese artists, and are scheduled for release in Denmark in June 2012.