1421 Esperanto in the outer asteroid belt at a distance of 2.8–3.4 AU once every 5 years and 5 months (1,983 days; semi-major axis of 3.09 AU). Its orbit has an eccentricity of 0.08 and an inclination of 10° with respect to the ecliptic. The body's observation arc begins with its first observation as at Heidelberg Observatory in October 1906, almost 30 years prior to its official discovery observation at Turku. This minor planet was named by the discoverer after the artificial language, Esperanto, which was created by inventor and writer, Ludwik Lejzer Zamenhof (1859–1917), who used the pseudonym "Doktoro Esperanto". The
Ludwik Birkenmajer of scholars. He was married Zofia (Sophie), the daughter of Franciszek Karliński, the professor of astronomy in the Jagiellonian University, and inherited his library embracing mostly the books on mathematics and physics. They had three sons: Aleksander Ludwik (historian of culture and exact sciences, and bibliologist), Józef (poet, interpreter and literature historian), and Wincenty (Polish philologist, teacher and renown Tatra Mountains-climber). His grandson is Krzysztof Birkenmajer (professor of geology, member of the Polish Academy of Sciences). In 2011 the Institute for the History of Science of the Polish Academy of Sciences received the name of father and son: Ludwik &