So, I have always been intrigued by this debate!  I think I have the best idea out there to answer this question once and for all!!!!   If the sun doesn't "set" or move around the globe, why doesn't someone launch a balloon during the night, say 1:00 am?  I have seen several balloon videos launched during the daytime showing what looks like a flat plane! If a night launch shows the sun at some point, I guess we can certainly put some factual data together and have the answer.  I don't know if this has been done.  If it has, I've never seen this.  I am just thinking logically!!.  Let me know what you all think....