This might seem easy, but to guess exactly what it is would be hard for most people. Give it a try before you read on.

Need a hint? Okay: It's a lot more down to Earth than you might think.

No more hints.

This is a photo of the exhaust plume billowing out from rockets launching a space shuttle. It's the shuttle Endeavour in a night launch Feb. 8, 2010.

On Monday (May 16) Endeavour is slated to launch at 8:56 a.m. ET for its last flight. [Update: Endeavour Launched.]

Gallery of Space Shuttle ImagesPrevious What the Heck imageGot a strange or interesting photo related to science, nature or technology? What the Heck, send it to me and maybe I'll use it. And you follow me on Twitter or Facebook.

The space shuttle Endeavour lifts off in the predawn hours from Launch Pad 39A in Kennedy Space Center in Floria on Feb. 8, 2010. (Image credit: NASA)