Is Earth unique in its fairly clear atmosphere? So, we have surface pictures from two alien planets, Venus (captured by the Venera 13), and Mars (captured by the rover).

Both of these pictures appear to be very dusty. For Venus we see strong storms; that makes sense. However, the Martian air also appears very dusty. Is Earth relatively unique in its clear atmosphere?



Mars



Venus



Titan (Thanks LocalFluff!)
Our atmosphere is only transparent to visible light, In most other wavelengths, some or all of the light is absorbed 

 
Image from Wikipedia, adapted from image by NASA

Our eyes have evolved to take advantage of the transparency at these wavelengths. If we had evolved in an atmosphere with a very different mix of gases. One in which visible light was absorbed, we would have evolved eyes that see different wavelengths.

There is a notable "window" at about $10\mu m$ in the diagram above. And you might wonder if any animal has evolved to see in this window. However, our own bodies emit thermal radiation at about $10\mu m$, eyes wouldn't work as they would be swamped by their own glow. However this window is used by thermal imaging devices.