Eye in the sky

As many a medieval castle-builder knew, the view from above is a privileged one.

Now, with its free Images of Change iPad app and online gallery, NASA makes the aerial perspective available to all, with results both stunning and disturbing.

For several decades, the agency’s Earth-observing satellites have been capturing dramatic views of land-changing events such as fires, tornadoes and mudslides. To see individual glaciers receding, however, the app’s ground-based photos showing green meadows replacing icebergs make the point best.

Urban change proves equally profound: An 1830s map alongside a satellite view of modern Boston shows that some of the country’s most expensive real estate occupies land that, until fairly recently, was underwater. 

Only some images are categorized as “human impact,” but nearly all of the changes on land — forest fire, glacier melt, flooding — clearly have a human component.

NASA does not explicitly make this point, but upon even a casual wander through the gallery, it makes itself.