I just came across OSXPlanet via MacUpdate.com. One of the reviews there mention that it's an app written by 15 year old Gabriel Ott.

It takes the NASA "cloudless earth" and "earth at night" images, projects them into whatever global projection suits your tastes, and can also overlay current cloud coverage. It also shows the day/night areas of the globe, showing either "cloudless earth" or "earth at night" as appropriate. VERY cool.

Just showed it to my wife, who normally uses a computer with a 10-foot pole, or assistance, or both. She was amazed. Cool.

Anyway, grab yourself a copy, and set it as a login item.