Centennial of Markov Chains
On January 23, 1913 of the Julian calendar, Andrey A. Markov presented for the Royal Academy of Sciences in St. Petersburg his analysis of Pushkin's Eugene Onegin. He found that the sequence of consonants and vowels in the text could be well described as a random sequence, where the likely category of a letter depended only on the category of the previous or previous two letters.
At the time, the Russian Empire was using the Julian calendar. The 100th anniversary of the celebrated presentation is actually February 5, 2013, in the now used Gregorian calendar.
To perform his analysis, Markov invented what are now known as "Markov chains," which can be represented as probabilistic state diagrams where the transitions between states are labeled with the probabilities of their occurrences.