This is very cool! Will definitely project on the ceiling.

I am struggling a bit with this explanation though:

> ZenithTrack shows a strip of the sky, a thin ribbon, one rice-grain tall, about 2,500 rice-grains long.

What does it mean to say "one rice-grain tall"? Is that angular diameter at arm's length?

yes. the Field of View is the size of a grain of rice at arm's length. the total "movie" you see is like 2500 of those rice-grains, end to end (earlier in the explainer, it mentions the FoV size)