Yesterday Google marked the 150th anniversary of the first aerial photo acquired in the U.S. They overlayed the photo (of what is now downtown Boston) on Google Earth imagery, and set it at the appropriate viewing angle in the video above.
In the scope of human history, aerial photography can seem like a very young technology. But for those of us watching the updates and advances roll out on a near-daily basis today, the 1860 image of Boston has a ghostly quality, as though we're looking into the past through a window that shouldn't exist. I often get a similar sensation when analyzing land surface changes over much shorter timescales - looking at forest mortality since 1980, for instance, or urban growth between 1970 and 1990. It seems like pixels should have a harder edge to them than memories, but they often feel like ephemeral impressions. This is especially true if they represent something lost like the Boston Common of 1860, or the Cornfields of South Burlington, VT in 1937: