When the respected astronomer announced that gravity’s effects would be briefly suspended, it got everyone’s attention. People who are accustomed to taking action in response to severe thunderstorm warnings, approaching blizzards, or civil defense emergencies listened carefully to find out what they would need to do on the day when everyone would experience a blip in gravity.

The news came from Patrick Moore (1923-2012), one of the most respected names in astronomy. His eccentric practice of always wearing a monocle only served to enhance his gravitas as he educated the public about the latest discoveries in the heavens. His television program The Sky at Night aired on the BBC from 1957 until his death.

When Moore took to the radio that day in April 1976, listeners were stunned as he announced that a rare celestial event would have a significant impact upon the residents of Earth. According to Moore, at 9:47 a.m. that day, a rare conjunction of Jupiter and Pluto would briefly cancel out a significant amount of Earth’s gravity. This phenomenon is known as the Jovian–Plutonian gravitational effect. While the full effects could not be accurately predicted, Moore did state that anyone who happened to be jumping in the air at that moment would certainly feel some momentary weightlessness.

Moore’s words were shocking. Even more surprising were the reports that started flooding in immediately after the predicted alignment. The BBC received hundreds of calls from individuals reporting their experiences. It seems that the effects were not uniformly distributed. Some said they noticed no effect whatsoever. Many others reported feeling at least some release from the relentless pull of Earth’s gravity. The most extreme situation was experienced at a home where a dozen friends had gathered. At the appointed time, all twelve of them “wafted from their chairs and orbited gently around the room,” according to the breathless caller.

It was only then that Moore reminded listeners of the date: April 1. His warning about the Jovian–Plutonian gravitational effect was just an April Fools Day joke. It was inspired by the best-selling book The Jupiter Effect by John Gribbin, which had recently been released. In the book, the author warned that unparalleled cataclysmic destruction would be unleashed on Earth on March 10, 1982, due to a predicted alignment of all of the planets.

In case you are curious, the disasters predicted in The Jupiter Effect did not come to pass. The most significant thing that might be attributed to the alignment was a 40-micrometer increase in the high tides. One month after the original date predicted for the destruction of the world, Gribbin released another book, The Jupiter Effect Reconsidered. In this book, he stated that the effect of the alignment had actually been felt two years earlier (before the planets ever aligned, interestingly enough), and it was the trigger for the Mount St. Helens explosion.

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