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.