Being proper geeks, a lot of us here at TUAW are amateur astronomers (we won't count Mel Martin, who is so incredibly good at astrophotography that he should be considered a professional). Although we've talked about numerous "planetarium" apps such as Pocket Universe, Star Walk, Distant Suns, and SkyVoyager, these apps simply show you what's going to be visible in the night sky at some specific point in time or show information about deep sky objects.
A new iPhone app from Water-Powered Ideas, Observation [US$4.99, iTunes Link] is designed to do something completely different. It lets you determine whether or not it's going to be worth taking the scope out tonight through forecasts from Atilla Danko's great Clear Sky Chart website, and then provides a way to log your observing sessions with your iPhone.
When you launch Observation, the app will ask if it can use your current location. When you tap the OK button, the app creates a list of "Nearby Charts." These are observing locations that have been entered into the Clear Sky Chart site. Once a chart has been chosen, the forecasted observing conditions at the site are displayed at the present time and for the next 18 hours. To flip through the hourly conditions, you simply swipe left or right.
The conditions show the general sky conditions with a weather icon, the current or forecasted temperature, the wind velocity, the humidity, and information on transparency of the sky and seeing. Transparency refers to how clear the atmosphere is (i.e., no smoke, smog, clouds, or dust would mean the sky is very transparent), while seeing describes how still the air is (very still air means excellent seeing).