5 April — memory beta

The 5th of April is celebrated as a holiday among several regions and species in the galaxy.

Among Romulans in the 25th century, this day is known as Republic Day, a celebration of the founding of the Romulan Republic on New Romulus. (STO mission: "Republic Day")

Events

Zefram Cochrane achieves Earth's first manned warp flight aboard the Phoenix.
Official first contact between Humans and Vulcans takes place when the surveyor T'Plana-Hath detects Cochrane's warp flight and follows his ship down to Bozeman, Montana. (TNG movie: First Contact, ST reference: Federation: The First 150 Years)

Aboard USS Endeavour, Captain T'Pol mind melds with a captured "Mute", giving her and Hoshi Sato more insight into their culture and communication.
USS Pioneer's science officer Reynaldo Sangupta detects biological signals from social animals not unlike whales while trapped in orbit of a super-Jovian planet. Doctor Therese Liao discovers Dax and learns about Trill symbionts while examining Tobin Dax for radiation damage.
Jonathan Archer and Charles Tucker III learn that Devna is the one manipulating Federation Defense Minister Min glasch Noar toward a more aggressive posture. (ENT - Rise of the Federation novel: A Choice of Futures)

2249: Amanda Grayson receives a message from T'Pau about Solkar's death. (TOS novel: Sarek)
2371: Captain S'alath dies on the Metron planet. (TOS - Unlimited comic: "The Veteran")
2377: USS Voyager detects Talaxian colonists on New Talax and sends the Delta Flyer II to make contact. (VOY episode: "Homestead")
2385: Attack on Mars: A500 Synths destroy Utopia Planitia Fleet Yards and ignite the stratosphere of Mars. (Short Treks episode: "Children of Mars", PIC episode: "Remembrance")
2409: Federation President Aennik Okeg begins an annual invitation to Alpha Quadrant Alliance COs to build and launch Phoenix replicas such as the Magenta Phoenix in celebration of First Contact Day. (STO - Reckoning mission: "First Contact Day Re-Enactment")
2410: USS Sovereign returns to service following assimilation by the Borg. (STO mission: "First Contact Day")

2063: When the T'Plana-Hath lands on Earth, Zefram Cochrane shoots Solkar and raids the ship. (ENT episode: "In a Mirror, Darkly")

2381: Fleet Admiral Leonard James Akaar schedules USS Titan to relaunch as a morale-boosting effort. (TNG novel: Losing the Peace)
2382: Commander Jefferson Briggs is arrested in Paris before the First Contact Day reception in the Palais de la Concorde. (VOY novel: Atonement)

1950: Novelist A.C. Crispin is born.
1968: TOS episode: "I, Mudd" airs as a repeat.
1969: TOS comic: "Beware the Beast" continues with its second of four weekly installments in Joe 90: Top Secret #12.
1978: TOS comic: "The Peril of Planet Quick Change" is released in Portuguese in O Caminho das Estrelas #4.
1980: The 28th installment of TOS comic: "The Real McCoy" is published in daily newspapers by the Los Angeles Times Syndicate.
1981: The 15th installment of TOS comic: "It's a Living" is published.
1982: The 36th installment of TOS comic: "The Wristwatch Plantation" is published.
1983: The 44th installment of TOS comic: "Send in the Clones" is published.
1993: TNG episode: "Lessons" airs (week of).
1997: DS9 episode: "Business as Usual" airs (week of).
2008: Remastered edition of TOS episode: "The Enterprise Incident" airs.
2012: STO - Vigilance mission: "Alpha" is released by Cryptic Studios.
2016: STO short story: "After the Storm" is released by Titan Magazines in Star Trek Magazine, Issue 183 (US #56).
2022: TNG reference: Star Trek: First Contact: The Making of the Classic Film is released by Titan Books.
2023: DS9 - The Dog of War comic: "Issue 1" is released by IDW Publishing.