Australian Dictionary of Biography entry: https://adb.anu.edu.au/biography/oconnell-daniel-joseph-kelly-15389

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Fr David Strong SJ, The Australian dictionary of Jesuit biography 1848-2015, Second Edition, 2017:
O'Connell, Daniel [includes a photograph]

Astronomer; born Rugby, England, 25 July 1896; died Rome, Italy, 14 October 1982, aged 86.

Daniel O'Connell's secondary education was at Clongowes College, Dublin. He entered the Society at Tullamore, Ireland, 8 September 1913, and juniorate followed at Rathfarnham, 1915-20. He received his diploma in experimental physics and a Master of Science degree in mathematics at the University of Dublin, and later a doctorate in science from the Irish National University. At this time he came under the influence of William O'Leary, the Irish Jesuit astronomer and seismologist, who at that time was director of Rathfarnham Castle Observatory in Dublin.

O'Connell then studied philosophy at Valkenburg, 1920-22, and did further tertiary studies in science, gaining first class honours in most subjects. It was while in Holland that he also pursued spare-time astronomical studies under world-famous Jesuit scientists like Michael Esch, expert on variable stars; Xavier Kugler, world authority on Assyriology and Babylonian astronomy; and Theodor Wulf, world ranking physicist.

Regency followed as assistant director of the Riverview observatory, 1922-26, as well as physics master and second division prefect. At this time he undertook to advance the local study of solar-radiation.

He went to theology at Milltown Park, Dublin 1926-29, and to tertianship at St Beuno's, Wales.

O'Connell studied from 1931-33 at Harvard College Observatory, Cambridge, Massachusetts, and was subsequently to have studied with the famous Sir Arthur Eddington. However, because of a lung condition, he returned to Australia, and then worked first as assistant director and later as director of the Riverview observatory, 1933-52. Then he was appointed moderator of the Vatican Observatory at Castel Gandolfo, Rome, 1953-70. He lived in the Jesuit Curia, Rome, and from 1974 was the president emeritus of the Pontifical Academy of Sciences.

During the years that O'Connell was at Harvard, the observatory was at the centre of major developments in astronomical research and especially those that were to lead within the next few decades to the notion of the expanding universe of galaxies. He was thus associated with such eminent astronomers as Harlow Shapley, Cecilia Payne Gaposhkin, and others. His principal occupation at Harvard, and a pursuit which continued for the rest of his life, was the study of variable stars; but he also became known as a keen card player, especially at bridge.

On his way back to Australia he visited Mount Wilson and Lick observatories in California, and then went to Japan, China, Java and the Philippines where he visited leading observatories and advanced his practical studies.

While at the Riverview Observatory, working under William O'Leary, and in addition to his study of variable stars, he developed a keen interest in seismology and in the measurement of time with various types of clocks. This latter focus led him into a life-long interest in the calendar and calendar reform, a study that served him well in later decades, since he was asked to advise popes on both calendar reform and the cycle of ecclesiastical feasts.

In 1935 he initiated the 'Riverview Observatory Publications', which enjoyed international reputation. Later, he founded the 'Reprint Series' and the Geophysical Papers that became also well known. In the field of astronomy, O'Connell worked on eclipsing stars and Cepheid variables. For the latter he used photo-electric equipment. About 15,000 plates on variable stars were on file at the observatory.

In the field of seismology the observatory's programme included the regional study of earthquake waves and the relationship between earthquake waves and the interior of the earth. During World War II, O'Connell collaborated with the United States government in the location of earthquakes in the Pacific zone in relation to war strategy. This work continued after the war. Each week a cabled report was sent to the United States from Riverview. The Imperial War Graves Commission also consulted him concerning possible earthquake damage to war cemetery sites in the Pacific area.

In his role as director of the Vatican Observatory, he began a career of unique service to the Church that spanned the reign of three popes, and saw immense developments in astronomical research from the initial concept of various stellar populations to an expanding universe containing active galactic nuclei and quasars. On a few occasions he organised study weeks of the Pontifical Academy of Sciences, at which was discussed e.g. Stellar Populations in 1957, and Nuclei of Galaxies in 1970. As a result of these study weeks, two books were published, both edited by O'Connell, and they became classics of astronomical literature. From 1955-61 he was president of the Commission on Double Stars of the International Astronomical Union.

Of his many contacts with popes he served, his relationship with Pius XII was especially close. He frequently advised the pope, himself a very keen and diligent student of the natural sciences, on topics of current scientific research. It was under Pius XII that the major modern research tool of the Vatican Observatory, the Schmidt telescope, planned under his predecessors but completed under O'Connell, was inaugurated and blessed. Pius XII often visited the observatory, and on one occasion viewed the launching of the Russian Sputnik.

Paul VI viewed the landing of the first man on the moon with O'Connell over a specially installed television, and he advised the pope on the technical details of the mission.

In the pursuit of his scientific research, O'Connell became a close friend and collaborator of an international community of astronomers. As director of the Riverview Observatory he went to Europe in 1948 to attend the first postwar meeting of the International Astronomical Union held at Zurich, and on that occasion visited many European observatories. His visit to Utrecht was noteworthy, for there he established a lifelong friendship with Professor Marcel Minnaert who later encouraged him to issue the now famous book on the Green Flash, which, published in collaboration with Brother Karl Treusch SJ, provides excellent documentation on optical effects which occur in the earth's atmosphere when the sun is rising or setting.

However, O'Connell was best known in the international community of astronomers for his research on double stars. He discovered an effect, since known as the 'O'Connell Effect', concerning the rotation of the line of the apsides (the major axis of the double star's elliptical orbit). The discovery of this effect was typical of the scientific work of O'Connell. It required a long period of painstaking observations and careful analyses over many years.

In addition to his membership in the academies and institutes already mentioned, O'Connell was a member of the National Research Council of Australia, and an honorary member of the Royal Irish Academy. He was also a member of the Royal Society of New South Wales, publishing three papers on earthquakes and the Galitzin seismograph. He served on council, 1946-49, and was vice-president, 1950-52. He became an honorary member of the Society in 1953.

O'Connell retired as director of the Vatican Observatory in 1970. He was president of the Pontifical Academy of Science, 1968-72. While he was an indefatigable worker and consequently very jealous of his time, he still treasured his friends immensely, and was, as a matter of fact, always nurturing new friendships. Even during his last years, when he was largely bedridden, he developed new friendships among old and young alike. The students at Riverview remembered him for showing groups of boys the moon, planets and the stars on clear nights and for his unfailing gracious word and cheery smile for staff and students.

Many were the nights that, under the then clear skies over Castel Gandolfo, O'Connell climbed the stairs to the telescope atop the papal palace passing the plaque inscribed: Deum Creatorum Venite Adoremus. He was very intelligent, hard working and always a gentleman: a genuine international Jesuit.

(Reproduced by permission of Fr David Strong SJ.)