June 6, 1761

1761 transit of Venus

The 1761 transit of Venus and Lomonosov’s disputed atmospheric observation

Mason and Dixon were attacked by a French ship on their way to Sumatra, and still managed to record the transit — from South Africa.

6 June 1761: Venus crosses the Sun

Venus passed between Earth and the Sun in 1761 and appeared to cross the solar disk. At St Petersburg the event fell on 26 May in Russia's Julian calendar, equivalent to 6 June Gregorian; NASA labels the transit 5 June, because it straddled the civil-date boundary.

Astronomers at widely separated stations — the Cape of Good Hope, Newfoundland, Siberia, India, Rodrigues Island — recorded contact times and visual effects for solar-parallax calculations, following the program Edmond Halley had urged.

NASA's accounting gives 176 scientists at 117 stations, not the round 120 locations often quoted.

Getting to a station in wartime

Charles Mason and Jeremiah Dixon observed successfully from the Cape of Good Hope after a French attack prevented their expedition from reaching its intended destination in Sumatra.

Jean-Baptiste Chappe d'Auteroche observed from Tobolsk in Siberia. John Winthrop, the Harvard professor, recorded the final portion of the transit from St John's, Newfoundland.

Lomonosov's bulge, and the argument about it

Mikhail Lomonosov observed from his own estate in St Petersburg, not the Imperial Academy's observatory, using a 4½-foot two-lens telescope and a deliberately light smoked-glass filter — he wanted to see the delicate moments when Venus touched the Sun's edge.

He reported a hair-thin brightness near ingress and a luminous bulge or flash near egress, and read them as refraction through a substantial atmosphere around Venus. He submitted his report on 4 July; 200 copies were published on 17 July 1761.

Priority is disputed. Pasachoff and Sheehan argue that Lomonosov was interpreting black-drop and instrumental effects; Shiltsev and later authors defend the atmospheric-aureole reading, and Chappe d'Auteroche, Torbern Bergman and Pehr Wargentin all reported effects that may have been genuine aureoles.

Sources

Researched 24 Aug 2026 7 sources not yet audited Date disputed

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Date disputed. Sources disagree about when this happened.

What the sources leave uncertain

The transit crossed the civil-date boundary: NASA labels it 5 June, while European and Russian accounts commonly use 6 June Gregorian. At St Petersburg, 26 May Julian equaled 6 June Gregorian.
Priority for discovering Venus’s atmosphere is disputed. Pasachoff and Sheehan argue that Lomonosov interpreted black-drop and instrumental effects, while Shiltsev and later authors defend the atmospheric-aureole interpretation.
Other 1761 observers—including Chappe d’Auteroche, Torbern Bergman and Pehr Wargentin—reported effects that may have been genuine atmospheric aureoles, complicating any exclusive priority claim.