The United States’ thermonuclear testing program Operation Castle commences with the first detonation, code named Castle Bravo, on a reef near Bikini Atoll. The most powerful hydrogen bomb detonation carried out by the American military during the 20th century, Castle Bravo has a yield of 15 megatons, three times greater than predicted, with a blast radius of over four miles. Radioactive fallout spreads over 7,000 square miles of the Pacific Ocean, including neighboring islands and a Japanese fishing boat, with both populations showing symptoms of radiation sickness shortly afterward, forcing evacuations and later reparations.
ABC airs the 46th episode of the supernatural anthology series One Step Beyond, hosted and directed by John Newland. Wesley Lau guest stars.
To further research into the formation and evolution of severe weather in the midwestern United States, the U.S. Weather Bureau establishes the National Severe Storms Laboratory in Norman, Oklahoma. Operating in close cooperation with the University of Oklahoma’s meteorology department and the Severe Local Storms Warning Service in Kansas City, the NSSL focuses on improving prediction and detection of destructive weather, including tornadoes, quickly fixating upon the potential of Doppler radar.
The 25th episode of Irwin Allen’s adventure series Voyage To The Bottom Of The Sea airs on ABC, starring Richard Basehart and David Hedison. John Anderson guest stars.
British broadcaster ABC airs the 101st episode of the spy-fi series The Avengers, starring Patrick Macnee and Diana Rigg. 
The 52nd episode of Irwin Allen’s science fiction series Lost In Space premieres on CBS, starring Guy Williams, June Lockhart, and Jonathan Harris.
For the second year running, NBC makes an announcement over the closing credits of Star Trek, reassuring viewers that NBC has picked up the show for a third season. Where the second season’s renewal was brought about by a substantial fan letter-writing campaign (with guidance from Gene Roddenberry), the third season pickup comes after fans stage protest marches outside NBC’s headquarters in Burbank and New York, having gotten word (from Star Trek fan Bjo Trimble, by way of Roddenberry) that the series is likely to be cancelled. The renewal is a double-edged sword, however: in the fall, NBC will move the series to Friday nights, a time slot where it’s virtually guaranteed to be cancelled at the end of its third season.
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ABC airs the 49th episode of Irwin Allen’s sci-fi series Land Of The Giants, starring Gary Conway, Don Matheson, Deanna Lund, and Don Marshall. 
NBC airs the 28th episode of Rod Serling’s Night Gallery, an anthology series of original short plays and short story adaptations hosted by Serling himself. Laurence Harvey and William Windom guest star.
The 275-pound, 18-foot filming “miniature” of the starship Enterprise from Star Trek arrives at the Smithsonian, but it’s just as well that its planned display in the National Air & Space Museum won’t open until 
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Despite the fact that a useful – and rare – alignment of the large outer planets will make a “Grand Tour” possible, NASA has only thus far funded a stripped-down version of the ambitious original Grand Tour plan, a pair of Mariner Jupiter/Saturn ’77 unmanned space probes (later renamed Voyager). Jet Propulsion Laboratory admits that scientists and mission planners have drawn up a “Uranus option” to extend the mission of one of the vehicles to reach Uranus four or five years after a Saturn encounter and gravity assist, and are making modifications to one of the vehicles to permit this contingency. (NASA has yet to approve continuing the MJS’77 program long enough to reach Uranus.) Mission planners also admit that a visit to Uranus could give the vehicle another gravity assist toward Neptune, while admitting that the odds of the vehicle surviving a journey to Neptune with its ability to gather images and scientific data intact would require “a miracle.”
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ITV airs the tenth episode of Roald Dahl’s anthology series Tales Of The Unexpected, hosted by the author himself and adapted from his short stories. Timothy West and Susan George guest star in the second season premiere.
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NASA launches Earth resource observation satellite Landsat 5, virtually identical to the Landsat 4 satellite launched in 1982. Like Landsat 4, Landsat 5 is capable of sending real-time data to Earth through the Tracking & Data Relay Satellite (TDRS) system. Landsat 5 becomes the longest-operating Earth observation satellite, outliving its anticipated three-year design life by a factor of ten and not becoming inoperable until 2013; by the time it was shut down, Landsats 7 and 8 had been launched. Among the events Landsat 5 witnessed from orbit were a tsunami that killed nearly a quarter million people along Indonesia’s coastlines in 2004, and the 1986 meltdown of the Chernobyl nuclear reactor in the Soviet Union.
Former Bourgeois Tagg frontman 
The ninth episode of a modern reboot of Dan Curtis’ gothic horror series Dark Shadows is broadcast on NBC, starring Ben Cross, Lysette Anthony, Roy Thinnes (The Invaders), and Jean Simmons. Adrian Paul (Highlander) guest stars.
The 95th episode of the syndicated series Superboy, starring Gerard Christopher and Stacy Haiduk, airs. This episode is a clip show.
The week-long national syndication window opens for 
The 14th episode of Roger Price’s rebooted science fiction series The Tomorrow People is broadcast on ITV in the U.K. (and will appear later on Nickelodeon in North America), starring Kristian Schmid, Naomie Harris (Spyfall), and Christian Tessier. Christopher Benjamin (Doctor Who) and Mac McDonald (Red Dwarf) guest star.
The week-long national syndication window opens for 
Premium cable channel Showtime airs the 30th episode of The Outer Limits, a revival of Leslie Stevens’ 1960s science fiction anthology series. Robert Foxworth (The Questor Tapes) and Teryl Rothery (Stargate SG-1) guest star.