Leonard initially focused his university research on double stars, which he studied using the facilities at Mount Wilson Observatory. (The equipments for astronomy teaching was very poor at that time but he got access to telescopes on Mt.Wilson and continued to observe stars and planets for some years).The University didn't obtain the research university mandate till after the World War II. Before shifting his focus to meteoritics he discovered at least 25 double stars. His interest in meteorites started in the mid to late 1920s. Leonard started corresponding with Harvey H. Nininger about meteorite purchases in 1930, and from that point forward, the majority of Leonard's contributions to astronomy surrounded his study of meteorites with a special focus on their systematics and statistics. In 1933 he founded The Society for Research on Meteorites, now known as the Meteoritical Society, with himself as president and Harvey H. Nininger as secretary. He accumulated a large collection of meteorites, examining them as part of his studies to form a revised and simplified meteorite classification scheme. Although the scheme's validity is still a subject of some controversy, it remains one of Leonard's most well-known contributions. Leonard translated his research into teaching material and offered the first class in Meteoritics at the university in 1937.He did his best for the Meteoritical Society to flourish and managed a lot of difficulties during WWII and especially after the war period.