Pacific Islands
In 1842, Tahiti and Tahuata were declared a French protectorate, to allow Catholic missionaries to work undisturbed. The capital of Papeetē was founded in 1843. In 1845,

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Astronomy
• April – Eta Carinae is temporarily the second-brightest star in the night sky.
• September 23, 1846 – Discovery of Neptune: The planet is observed for the first time by German astronomers Johann Gottfried Galle

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• In the mid-1840s several harvests failed across Europe, which caused famines. Especially the Great Irish Famine (1845–1849) was severe and caused a quarter of Ireland's population to die or emigrate to the United States, Canada and Australia.

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Literature
• Charles Dickens publishes The Old Curiosity Shop, Barnaby Rudge, A Christmas Carol

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• The American Transcendentalism movement is in full form mostly during this decade.
• February 1840 – The Rhodes blood libelis

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• January 13, 1840 – The steamship Lexington burns and sinks in icy waters, four miles off the coast of Long Island; 139 die, only four survive.
• May 7, 1840 – The Great Natchez Tornado:

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Women's rights
• July 19, 1848 – Women's rights, 1848 – Seneca Falls Convention: The 2-day Women's Rights Convention opens in Seneca Falls, New York,

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