Nemiroff said his favorite April Fools' Day Astronomy Picture of the Day was posted in 2001. The image shows two space shuttle astronauts on a space walk. The two were described as playing the historic first "Space Quidditch" match. Quidditch is a fictional game played by wizards in the popular J.K. Rowling's popular Harry Potter novels.
"I hope that astronauts will actually make up a game like Space Quidditch one day," Nemiroff said.
Bonnell, meanwhile, said his favorite April Fools' Day posting is a 1999 picture of "snow fields" on Mars imaged by the Mars Global Surveyor spacecraft. Bonnell titled the image "Ski Mars!"
"It must have been about the time my kids were learning to snowboard, and I was trying to keep up with them," Bonnell said.
Text notes accompanying the photo noted that the planet's uncrowded slopes indicated expensive lift tickets but that "a vacation on the red planet could still offer some advantages to skiing or snowboarding enthusiasts. For example, Mars' low gravityonly about [three-eighths] Earth's gravitywould definitely tend to reduce sore muscles and fall-related injuries."
Other hoax images include 2002's slightly altered picture of the moon, purporting to show a numeric date in one of the craters. The image was titled "Hubble Resolves Expiration Date for Green Cheese Moon." The image was actually taken in 1965 by the Ranger 9 spacecraft moments before impact.
For April Fools' Day 2003, Nemiroff and Bonnell posted a picture of the underside of a bird's talons. The bird had been perched on a camera at the Cerro Tololo Inter-American Observatory in Chile. The caption: "A New Constellation Takes Hold."
"April Fools' Day is supposed to be fun. We try to keep this in mind and even have fun ourselves when writing these up," Nemiroff said.
When Bonnell and Nemiroff started the Astronomy Picture of the Day, it forced them to look beyond their field of gamma ray astronomy to find something interesting to post each day.
As Bonnell put it, producing the site "makes us every once and a while stop and look around and smell the astrophysical roses and see what everybody else is up to."
Now, with the popularity of the Web site, their e-mail boxes are flooded with pictures and suggestions from their fans around the world. April Fools' Day is among the most popular days for fans to submit images for.
The current interest in Mars, and the stream of images beamed down to Earth from the various spacecraft roving and orbiting the planet, made 2004's hoax a no-brainer, Bonnell said.
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