Brazilian astronomer crossed the world to see Venus – 03/17/2024 – Science

On December 9, 1874, in Nagasaki, Japan, where he arrived after a 48-day journey by ship, the Rio de Janeiro astronomer and engineer Francisco Antonio de Almeida Júnior (1851-1928) described in this way the rare passage of Venus in front of the Sun : “At 10 hours and a few minutes we witnessed the triumphal entry of Venus into the solar regions, and more than a century had already passed since the beautiful goddess did not deign to allow mortals to witness her ardent visits to the king of the stars.”

The report is part of his book “From France to Japan: Travel Narration and Historical Description, Uses and Customs of the Inhabitants of China, Japan and other countries in Asia”, published in 1879.

Considered the first Brazilian astronomer to follow a transit of Venus and the first citizen of the country to visit Japan, Almeida was part of one of the French teams, as he had been studying in Paris since 1872. An Italian team had gone to India, a French team, to New Zealand and a British one, to Hawaii, all with the same objective: improving the values ​​of solar parallax. This term “indicates a change in the apparent situation of the star to which it refers”, explained Almeida Júnior in the book “A Paralaxe do Sol e as Passagens de Vênus”, from 1878. In other words, it is the apparent displacement of a celestial object – in this case , Venus – on the solar disk, seen from different points on the globe.

With data on the planet’s displacement on the solar disk, astronomers calculated the distance between the Earth and the Sun, the so-called astronomical unit. “They were looking for more precise values ​​of the dimensions of the Solar System”, explains astronomer Rundsthen Nader, from the Valongo Observatory and the Federal University of Rio de Janeiro (UFRJ), who studied Brazilian participation in the Venus transits of 1874 and 1882 in his doctorate, completed in 2015.

The 1874 phenomenon was the eighth recorded, on the trail blazed by British astronomers Jeremiah Horrocks (1618-1641) and William Crabtree (1610-1644). Separately, from their homes near Preston and Manchester, both in the United Kingdom, they were the first to make a scientific observation of the passage of Venus in front of the Sun on December 4, 1639.

“This observation had setbacks and Horrocks and Crabtree didn’t even try to determine the parallax of the Sun”, says astrophysicist Oscar Matsuura, retired professor at the University of São Paulo (USP) and organizer of the book “História da Astronomia no Brasil” (Cepe, 2014) . “Then, Horrocks, based on the angular diameter [diâmetro aparente, medido da Terra, em graus] of Venus, estimated the distance from the Sun to be 97 million km [quilômetros]indicating that the Solar System was much larger than previously believed.”

The Italian astronomer and mathematician Giovanni Cassini (1625-1712), in Paris, and his assistant Jean Richer (1630-1696), in Cayenne, French Guiana, observed the parallax of another planet, Mars, in 1672, obtained the first reliable measurement of the astronomical unit, of 138 million km, which remained for about a century.

Observing the passage – or transit – of Venus and Mercury, the two planets closest to the Sun, was then one of the main means of calculating the distance from Earth to our nearest star. Mercury sets in front of the Sun about 13 or 14 times each century, while transits of Venus occur in cycles of 243 years, which begin with a first passage, in December; eight years later, again in December, there is a second one; there is an interval of 121.5 years until the third, in June; eight years later, also in June, the fourth transit occurs; the next one takes place 105.5 years later, also in December.

The idea of ​​using the passage of a planet to calculate the distance between the Earth and the Sun was proposed in 1716 by the British astronomer Edmond Halley (1656-1742), after witnessing a transit of Mercury in 1677 on the island of Saint Helena. His hypothesis was that it would be possible to calculate the distance from Earth to the Sun by triangulation, measuring the passage of another planet from different points on Earth. “The position of Mercury’s transit was more difficult to observe, as it made a trajectory just above the horizon. So, at that time, Venus was the hope”, says Nader.

In a chapter of the book “Epistemología e História de La Astronomía” (University of Córdoba, 2023), physicists Maria Romênia da Silva and André Ferrer Pinto Martins, both from the Federal University of Rio Grande do Norte (UFRN), observe that Almeida was a key character in Brazilian astronomy at the time and “expresses the desire and commitment of a generation of intellectuals interested in better understanding the country, with ways of making it advance based on European references”.

Almeida arrived in Paris in 1872, with a colleague from the Imperial Observatory of Rio de Janeiro, the astronomer Julião de Oliveira Lacaille (1851-1926), both with scholarships granted by Dom Pedro 2º (1825-1891). “Until then, there was a utilitarian astronomy in Brazil, which was used to determine schedules and help with geographic measurements for the construction of roads, while in Europe researchers were already trying to understand the chemical composition of stars”, observes Nader.

The changes in Brazilian astronomy had begun a year earlier, in 1871, when the emperor invited the French astronomer Emmanuel Liais (1826-1900) to direct the Imperial Observatory in Rio de Janeiro. Liais accepted, under two conditions: the institution would no longer focus on training military academy students and would invest in astronomical research, including basic science. “It cannot be denied that the emperor prepared the conditions for Brazil to participate significantly in the international effort to observe the transit of Venus in 1882”, highlights Matsuura.

In Nagasaki, Almeida Júnior operated innovative equipment, the photographic revolver, developed by the leader of the French team, astronomer Pierre Jules Janssen (1824-1907). The device worked like a rudimentary camcorder and was used to record images of the moment Venus touched the solar disk in sequence with very short time intervals on glass plates with silver emulsion. The result, however, was not what was expected. “The images were grainy, which prevented a thorough analysis of the planet’s position,” says Nader. “The French mission in Nagasaki contributed very little to the improvement of solar parallax. In general, the data from 1874 were not very different from what was already available.”

In 1875, while still in Europe, Almeida received the Brazilian commendation of Knight of the Order of the Rose for his participation in the French scientific commission and returned to Rio de Janeiro the following year, with a doctorate in philosophy from the University of Bonn, in Germany. “He wrote a thesis on air movements, motivated by the fact that he emerged unharmed from a typhoon that left around 8,000 people dead in the city of Hong Kong when he was traveling to Japan with the French commission”, says Silva.

Brazilian participation was most relevant in observing the transit of Venus in 1882, this time visible in South America, Central America and eastern North America. One team stayed at the Imperial Observatory, now under the direction of the Belgian astronomer Luiz Cruls (1848-1908), and others went to Olinda, in Pernambuco, Punta Arenas, in Chile, and the island of São Tomás, in the Antilles.

Expenses on expeditions motivated debates about science financing in the country. “In 1874, there was some criticism about sending an astronomer to Japan, but on a much smaller scale”, reports historian Jacques Pinto, from the Casa de Oswaldo Cruz of the Oswaldo Cruz Foundation (Fiocruz). This time, the ministries of the Empire and the Navy placed an order for 30 contos de réis, each, for the manufacture of telescopes, construction of observation houses, transportation and payment of researchers.

Deputies and senators from the Liberal and Conservative parties voted together against releasing the funds. “A utilitarian view predominated, that science would have to focus only on farming and agronomy”, observes historian Alexandra Aguiar, from the State University of Rio de Janeiro (Uerj), who examined the political clash in an article published in August 2017 in Temporalidades magazine. Finally, on May 30, 1882, only the request from the Ministry of the Empire was approved. Private donations completed the remainder of the funds requested for the Antilles mission, headed by Antônio Luís von Hoonholtz, the baron of Tefé (1837-1931).

Cruls headed the Punta Arenas commission and published the Brazilian observations in December 1887 in the Annales de L’Observatoire Impérial de Rio de Janeiro. According to Nader, the final value for solar parallax obtained by the Brazilian commission was 147,826,661 km, because Cruls did not include the errors associated with the measurements, as expeditions from other countries did. “In academic circles, the results of the Brazilian commission were well received,” says Nader.

Lacaille, who had also studied in France, headed the team that set up an observation point in Olinda, but there are no records of Almeida Júnior’s participation in any of the Brazilian expeditions in 1882. His absence “seems to this day inexplicable, even considering the opinions of astronomers who did not believe in the advantage of observing the passages of Venus to determine the solar parallax”, commented astronomer Ronaldo Rogério de Freitas Mourão (1935-2014), from the Museum of Astronomy and Related Sciences (Mast), in a 2005 article in Navigator magazine.

By analyzing the 94 pages of the book “A Paralaxe do Sol”, Silva verified that Almeida indicated the times when Venus would probably be visible in cities in Brazil, Chile, Peru, the United States, Canada, France and Scotland in 1882. “He gives understand that I expected to be invited to join the Brazilian delegation”, she concluded. In his view, the political tensions of the time could explain the fact that he was left aside: “He aligned himself with liberal ideas, and the political atmosphere in 1882 was complicated for Dom Pedro 2º, as the clashes over funds had already indicated to finance scientific commissions”.

Appointed director of the Official Gazette in July 1891, Almeida was dismissed from his position six months later, when President Deodoro da Fonseca (1827-1892) resigned. He was later arrested under President Floriano Peixoto (1839-1895) accused of participating in a conspiracy against the government in April 1892. “He was critical of the military governments of the First Republic, known for being authoritarian”, comments Pinto.

At the end of the 19th century, instead of waiting for other Venus passes, astronomers began to calculate solar parallax using asteroids, rocks of different sizes that orbit the Sun. Then, they used radar and the speed of light. In 1976, the International Astronomical Union (IAU) fixed the distance between the Sun and the Earth at 149,597,870 km.

In 2008 and 2012, Venus once again crossed the solar disk. “But these transits didn’t add much more information about these measurements. Just like eclipses, today they are more media events, which help to disseminate science”, ponders Nader. The most easily visible planet in the sky is expected to appear again in front of the Sun on December 10, 2117 and December 8, 2125.