This photograph, taken by Marc Ferrez on December 6, 1882, is contained in an album that commemorates the participation of Brazil in the international effort to track the transit of Venus that same year. Ferrez honored Brazil’s contribution by compiling a photomontage of the three men commissioned by the Imperial Observatory of Brazil to view the transit on the island of St. Thomas in the Antilles. Antonio Luiz von Hoonholtz Tezpur, the Baron of Teffé, is shown at the top of the picture. Captain Lieutenant Francisco Calheiros da Graça is on the lower left. Lieutenant Arthur Indio do Brazil e Silva is on the lower right. Tracking the transit involved the establishment by the Imperial Observatory of an observatory, named after Emperor Dom Pedro II (1825-91), on the island of Saint Thomas in the Danish West Indies (present-day U.S. Virgin Islands). The transit of Venus is a rare astronomical event that occurs when Venus passes between the Earth and the sun, becoming visible in daylight against the solar disk. The transits occur in eight-year pairs at intervals of more than a century. Since the 17th century, astronomers had been especially interested in these transits, as they offered the chance, using multiple observations and complex mathematical calculations, to determine the distance between the Earth and the sun (the Astronomical Unit). There thus was great scientific as well as public interest in the transits of 1874 and 1882. Ferrez was one of Brazil’s most prolific photographers. He was instrumental in chronicling the development of Brazil at the end of the 19th century. The album is part of the Thereza Christina Maria Collection at the National Library of Brazil. Composed of 21,742 photos assembled by Emperor Pedro II throughout his life and donated by him to the national library, the collection covers a wide variety of subjects and documents the achievements of Brazil and Brazilians in the 19th century. The collection, named after Empress Thereza Christina Maria, was inscribed on the UNESCO Memory of the World register in 2003.