Pebble in the Sky

A science fiction book by Isaac Asimov about a time trip by an elderly man from the mid-twentieth century to a time when the Earth has been rediscovered by humans who have colonized the galaxy and forgotten that Earth is their ancestral home. I found it to be very moving, and it is still one of my favorite books, although both Asimov and the genre moved ahead in the quality of writing as time went on.

Pebble in the Sky was Isaac Asimov's first ever published Science Fiction novel and it is one of the books in the Empire series which is the precursor to the Foundation series. It includes The Currents of Space and The Stars, Like Dust. This series was written very early on in his writing career and it sometimes shows. Also, over time it was proved that many of the Science Fiction elements in this series were actually incorrect. Things like radiation's effect on humans and such.

As such, the series is not in print anymore. However, if you frequent used book stores you can usually get a set in a couple of years.