I'm sure you've seen Google Earth professional used on the news. Anytime a broadcast "flies" to a destination and then zooms into a location on the earth - odds are - they are using Google Earth. That's really cool but what does it have to do with genealogy.
Well, Google Earth also has a gallery of special photo tours and events. This includes a timeline tour of London starting in 1953, tsunami mapping, shoreline changes, and much more.
Many of my ancestors spent much of their lives in Philadelphia, PA. With Google Earth I can see what their home looks like now (if they are still there.) I can also see what churches and schools are around their addresses. I was even able to locate local cemeteries. The church and cemetery records are wonderful sources for family documents.
Google Earth is a downloaded free piece of software that allows you to travel all over the world from your computer and with the timeline function, you can look at satellite views from prior years. That's cool, but that's not all.
Have ancestors from New York City? I do. Google Earth has antique map overlays which overlay an old map over the current map. This way you can track street name changes and maybe finally find the neighborhood your great-great grandfather grew up in.
So, happy travels.