Short answers, pulled from the story.
The Penny Black, issued on the 1st of May 1840, was the world's first postage stamp. It allowed senders to prepay postage for a single penny and became valid for use from the 6th of May. It was part of the broader Uniform Penny Post reform introduced in the United Kingdom on the 10th of January 1840.
Pyotr Ilyich Tchaikovsky was born on the 7th of May 1840, Claude Monet on the 14th of November, and Auguste Rodin on the 12th of November. The year also saw the births of Thomas Hardy on the 2nd of June, Émile Zola on the 2nd of April, and the painter Odilon Redon on the 22nd of April.
The World Anti-Slavery Convention was organized by the British and Foreign Anti-Slavery Society and held at Exeter Hall in London from the 12th to the 23rd of June 1840. A major controversy arose over the exclusion of women from the convention proceedings, and the arguments that followed had direct consequences for the women's suffrage movement in the United States.
Two separate Antarctic discoveries occurred within days of each other in January 1840. On the 19th of January, Captain Charles Wilkes of the United States Exploring Expedition sighted what became known as Wilkes Land in the southeast quadrant of Antarctica, providing evidence that Antarctica is a complete continent. On the 21st of January, French explorer Jules Dumont d'Urville discovered Adélie Land and claimed it for France.
British colonists officially founded the settlement of Wellington on the 22nd of January 1840. The Treaty of Waitangi, granting British sovereignty, was signed on the 6th of February. New Zealand was formally declared a British colony on the 21st of May 1840.
Notable deaths in 1840 included Niccolò Paganini, the Italian violinist and composer, on the 27th of May; Caspar David Friedrich, the German Romantic painter, on the 7th of May; Fanny Burney, the English novelist, on the 6th of January; and Siméon Denis Poisson, the French mathematician, on the 25th of April. Anne Lister, the English diarist later described as "the first modern lesbian," also died on the 22nd of September 1840.