On April 1, the online world becomes even less reliable and more shadowy than normal. Most online japes are either not very funny, not very believable, or neither. You really can't believe anything you read that's posted — and on April 1 it doesn't much matter.
But some pranks are real, and have real consequences.
After Apollo 11's spectacular success, it was felt that Apollo 12 had to up the ante to keep people interested. As well as being a more relaxed mission — commander Pete Conrad made a $500 bet with a reporter that his first words on the moon would be "Whoopie! Man, that may have been a small one for Neil, but that's a long one for me" — the moonwalkers were given a colour, rather than Apollo11's monochrome, TV camera, albeit one with a much more delicate tube.
That wasn't to be the only colour on the otherwise starkly colourless lunar surface.
After landing on November 19, 1969 (and winning his bet), Conrad deployed the colour TV camera but found that it wasn't working at all well — the Secondary Electron Conduction (SEC) tube was very prone to overload and flared out easily. These problems had been anticipated due to issues found during pre-flight training, but nobody was sure what the actual lunar surface lighting conditions would be. Apollo 11 had landed at a different time of lunar day, after all. Thus, Conrad's lunar excursion checklist included a calibration test cad to set things up on location — something he had extensively practised.
During the calibration and set-up, the TV link up to the orbiting command module and thence back to Earth was active but not forwarded to the TV networks. This was ostensibly out of concern that viewers would get confused by the various test signals but in reality because NASA, already very sensitive to its image, wanted the first colour pictures from the lunar surface to be pristine, compared to the historic but hard to understand images from Apollo 11's live feed.
This reticence was just as well. Knowing that the set-up would not be broadcast, Command Module pilot Richard "Dick" Gordon had secretly got at Conrad's checklist [NASA PDF, NSFW] and among other additions had pasted the October Playmate Of The Month (Jean Bell) from Playboy over the calibration chart.
Conrad knew nothing of this until, half an hour into his first lunar EVA, he set up the camera for the test and turned to the appropriate page. Instead of the expected gray scale, colour bars and resolution gratings, however, he saw Ms Bell in all her glory.
Although the TV signal wasn't being broadcast, the mission audio was. Conrad choked back his initial reaction, set up the 'test card' and started an earnest discussion with Gordon orbiting in the CSM about front porches and blooming (fortuitously genuine video tech terms), surface features and other apparently legitimate matters. However, somewhat distracted, he didn't adjust the controls properly for a few minutes until Mission Control gently reminded him of the mission in hand — whereupon he removed the photograph to reveal the proper test card underneath. (The discarded photo remains on the lunar surface to this day, for all mankind.)
There is a phenomenon in early TV cameras called burn-in, where an image that has been present for too long leaves a permanent trace on the image. It normally takes a long time — but the early, crude technology of the SEC tube, the very harsh light of the moon and Conrad's extended funbling had overloaded the phosphor. Ms Bell's surface features, in ghostly negative, overlaid everything.
Mission Control was horrified. With the world waiting and options limited, they tried everything they could think of, but there wasn't much time and even fewer options. As a last-ditch attempt, they asked Conrad to try pointing the camera directly at the sun: this erased the Playmate but also burned out the camera. Just forty minutes after turning it on for the first time, it was useless. At least NASA had a plausible excuse for the failure and, delightfully for the moon-landing denialists, could embark on a very minor lunar cover-up.
There was no back-up. The Apollo 12 lunar surface mission returned no live TV surface pictures after the burn-out, leaving the networks cool about the extended coverage — the start of a decline in interest in Apollo that, even with Apollo 13's spectacular rescue, led to an early close-down of the project. Instead of going to Apollo 20, the last mission was Apollo 17.
Which was particularly harsh on the crew of Apollo 18 — and especially on the commander, who had previously come very close to the Moon and "wanted to land so badly, I could taste it." His name? Dick Gordon. For a prank to go so badly wrong is truly unbelievable.