Daniel Kirkwood (September 27, 1814 - June 11, 1895) was an American astronomer. Born in Harford County, MD, he was graduated in mathematics from the York County Academy in York, PA in 1838. After teaching there for five years, he became Principal of the Lancaster High School in Lancaster, PA, and after another five years he moved on to become Principal of the Pottsville Academy.

Edward Singleton Holden (November 5, 1846 – March 16, 1914) was an American astronomer.

He was born in St. Louis, Missouri in 1846 to Jeremiah and Sarah Holden. From 1862-66, he attended Washington University in St. Louis, where he obtained a B.S. degree. He later trained at West Point in the class of 1870.

George Ellery Hale (June 29, 1868 – February 21, 1938) was an American solar astronomer.

Sir Sandford Fleming, KCMG (January 7, 1827 – July 22, 1915) was a Scottish-born Canadian engineer and inventor. He proposed worldwide standard time zones, designed Canada's first postage stamp, left a huge body of surveying and map making, engineered much of the Intercolonial Railway and the Canadian Pacific Railway, and was a founding member of the Royal Society of Canada and founder of the Royal Canadian Institute, a science organization in Toronto that served as landlord to the office of the Royal Astronomical Society of Canada between 1898 and 1946.

Nicolas Camille Flammarion, Commandeur-Légion d'honneur (26 February 1842—3 June 1925) was a French astronomer and author. He was a prolific author of more than fifty titles, including popular science works about astronomy, several notable early science fiction novels, and several works about Spiritism and related topics. At the age of nineteen, he published his first work, La Pluralité des Mondes Habités, which caught the public taste and was at once translated into several languages.

Sir George Howard Darwin KCB FRS (9 July 1845 – 7 December 1912) was an English astronomer and mathematician.