years at different European observatories. He traveled to Italy, the German city Heidelberg and the French cities of Paris, Meudon, and Lyon. He also visited the English cities of Greenwich and Cambridge constantly participating in astronomical research. While he was at Cambridge he studied with Professor Sir Arthur Eddington. Plakidis and Eddington published a paper entitled the Irregularities of the Period of Long-Period Variable Stars which attracted international attention and by 1931 Plakidis was awarded a Ph.D. He returned to Athens and was awarded a position at the University of Athens after the death of Eginitis in 1934. Around the same period, he became the director of the Astronomical Institute of the National Observatory and frequently served as chairman of the National Observatory. While he worked at the National Observatory of Athens he developed new instruments and added a section for solar physics. One year before the Space Race began in 1954 Plakidis spent one year at the Yerkes Observatory in the United States of America. He also participated in the establishment of the Penteli Observatory containing a 63 cm Newall telescope which was donated by Cambridge University in 1955 because of Plakidis's lifelong research relationship with Sir Arthur Eddington. Plakidis continued his research on variable stars throughout his life writing papers for different local and international publications. He published books on spherical astronomy, astrophysics, and practical astronomy. He was an observational astronomer. Some of his observations were published in the Annals of the Academy of Athens, Annales de l'Observatoire National d'Athenes, Royal Astronomical Society, Harvard College Observatory Bulletin, Astronomische Nachrichten, Journal des Observateurs, Ciel et Terre, Comptes rendus de l'Académie des Sciences, and Bulletin de l'Observatoire de Lyon. He made systematic observations on variable stars, double stars, novae, solar eclipses, stellar parallaxes, and the planets Mars, Jupiter, Saturn, and Mercury. He was the first director of the Evgenides Planetarium and developed the facility. He retired in 1964 and became honorary director of the Astronomical Institute and emeritus professor at the University of Athens. He continued observational astronomy until his death. In 1974, he independently discovered V1500 Cygni several hours after Minoru Honda registered the discovery in Japan. That same year he was honored by a publication of his works entitled In honorem S. Placidis :special volume dedicated to Professor S. Plakidis on his 80th birthday. He died on January 30, 1991, at 97 years old. Publications References Bibliography 20th-century