NavList:

Yes, the Google Ngram viewer is fascinating! I also checked in with Google Trends. Here's a comparison on Trends of "terrestrial navigation" and "astro navigation". I included the latter only because it helps to illustrate that the trends are not normalized in the long-term; the apparent decline from 2004 is not real, in other words. It does show that both of these phrases are uncommon in the modern world. As we've discussed other times, celestial navigation seems to have edged out the formerly dominant astro-navigation even in British usage. Notice that "terrestrial navigation" has some interesting spikes in June for several years. That's the beginning of the busy boating season in the northern hemisphere, and I assume it's connected in some way. Maybe classes are offered with that title seasonally.

Frank Reed