Astronomy Picture of the Day Astronomy Picture of the Day (APOD) likes to make little jokes on April 1, usually re-captioning existing images. For example, on April 1, 2003 it reported that a new constellation was surprising star gazers. The constellation of Ollie the Owl has suddenly started dominating the southern hemisphere. The picture showed a bird perching on the Tololo All Sky Camera, and APOD admitted that it would have been funnier if the bird hadn't scratched the plastic dome.

However on March 31, 2005, APOD showed the next day's picture as water on Mars . . . which did leave people wondering. This was before orbiters and rovers had gathered considerable evidence of water on the red planet. The April 1 picture was of a glass of water on top of a Mars bar.

Mercury's moon On March 31, 2012 NASA provided the discovery image of a moon for Mercury, as captured by the MESSENGER spacecraft. Even on the eve of April 1, this was credible after all, spacecraft often discover moons. But like many good April Fools, there are clues.

Firstly, the enlarged picture of the moon is immediately recognized by many astronomy buffs. It's a well-known image of asteroid 243 Ida, taken by the Galileo spacecraft on its way to Jupiter.

Secondly, they outlined the plan to collide MESSENGER with the moon to knock it free of Mercury's gravity and set it on an Earth-crossing trajectory suitable for recovery as a Mercury meteorite. In fact, they'd do this with such precision that the moon would arrive at a remote location in Antarctica, avoiding population centers. Whew! Pretty impressive planning for something that had only been discovered the day before!

And finally, there's a mission proposal in the planning stage for X-ray analysis of Mercury's surface. It's name: Hermean On-surface Analysis with X-rays. (What's its acronym?)

Astronauts April Fool in space, 2010. The three-man crew of the International Space Station got a laugh out of Mission Control with a doctored photo of themselves spacewalking - not wearing space suits, but slacks, T-shirts and sunglasses. (Hope they remembered their sunblock!)

On April 1, 2013 Canadian astronaut Chris Hadfield tweeted a picture of himself with two space grenades, which were actually air sampling devices. And during the day he tweeted a series of images of an unidentified object nearing the Space Station. I imagine his followers had worked out the April Fool long before the final picture of him with a little green alien. "I don't know what it is or what it wants, but it keeps repeating 'Sloof Lirpa' over and over. Alert the press." (The alien message isn't so strange if you read it backwards.)

The Jovian-Plutonian Gravitational Effect The online Museum of Hoaxes lists Patrick Moore's April Fool as one of the 100 Best Hoaxes. The popular British astronomer, with the help of BBC radio, explained the Jovian-Plutonian Gravitational Effect to listeners on April 1, 1976. He said that at 9:47 a.m., a rare conjunction of Jupiter and Pluto would partially negate Earth's gravity and that if you jumped at that time, you would get a floating feeling.

A number of people later phoned the BBC to describe their experiences of floating. I don't know if they were serious or were joining in on the joke.

Go here to read the rest:

Astronomy April Fools