This. While it wasn't Celestia (I was playing around with Orbiter), I ran into a very similar, very specific scenario. In Orbiter, you can fly to planets using orbital mechanics a la KSP but on a true scale. Frustrated that I was having trouble getting to Saturn using a Hohmann transfer, I eventually said fuck it and just input coordinates that put me just a little ways outside of Saturn's atmosphere.

Upon hitting the button to warp to the coordinates, I was presented with an entirely flat, beige plane. Thinking I had screwed up the coordinates, I began zooming out. Since Orbiter renders to scale rather than the scaled down planets in KSP, I began to realize that there was no mistake, and just how small my ship was relative to Saturn. It literally gave me a shiver. It's so hard for us humans to really perceive how mindbendingly big things are in space in a direct sense.