There are plenty of Planet earth desktop backgrounds but there are few that work in real time like OSXplanet.
OSXplanet is a live desktop program based on the popular program, Xplanet. It generates live images of Earth on your desktop with additional information such as the current cloud conditions, storms, satellites, volcanoes, earthquakes and local time and locations of cities. Now, this might not sound useful - and it isn't really unless you're a frequent world traveler - but it does look quite good.
On installation, OSXplanet installs itself on your desktop immediately without any prompting which is a bit annoying as it should really warn you that your current desktop is about to disappear. However, as soon as you shutdown OSXplanet, your original desktop returns. What you see is a map of the Earth in real time with the current lighting conditions illustrated across the map - so at the time of writing, Europe and the Americas are in the sun light while the Eastern hemisphere is plunged into darkness.
However, it's not clear where the supposed cloud, earthquake and satellite data are. You can administer OSXplanet from your top toolbar although this also is not really explained when you install the program so you need to find it yourself. It's also rather unstable - I experienced two crashes within the first 5 minutes.
OSXplanet looks great on your desktop although do you really need to see the Earth's real time lighting conditions unless you work for NASA?
