Astronomy's Lingua Franca

Data collected for the Historical Astronomy Division's Astronomy Genealogy Project (AstroGen: https://astrogen.aas.org/) can be used for many purposes. One example is to study the evolution of the language used in astronomical writing, as shown by doctoral theses (dissertations) over the past 175 years. We examine the languages used in several countries where we have a "nearly complete" data set and where English is not the primary language. Latin predominated for astronomy-related theses written in Europe until about 1870. After that, the national language was usually used. Gradually, English took over in most of these countries, to the point where today a student can earn a Ph.D. in any of a number of non-English speaking countries without ever learning the local language. Since the year 2000, the majority of astronomy-related doctoral theses have been in English in Austria, Denmark, Finland, Israel, Netherlands, Sweden, and Switzerland, and if we only go back to 2010, we can add Germany and Spain to this list. Just as the universal knowledge of Latin among European scholars once made it easier for the German- and Polish-speaking Copernicus to study in Italy, today a knowledge of English enables students from anywhere to study almost anywhere.