Since we talk bout astronomy, there is another interesting point regarding the "weather" in OP:
Enies Lobby is an island without night. I wonder if Oda will explain that by placing an isle in the NW without daylight. Cause that would mean EL as well as the other island are always pointing at the sun/covered by the planet himself and cut off of the daylight.
Oda's inspiration for EL sure came from Scandinavia (IDK exactly which country, Finland or Norway) where in one whole summer night there is no dusk so the sun shines for more than 24 hours. Skadi is Scandinavian iirc, she could know which country I mean.
I know this is Shonen after all, but Oda also linked certain weather phenomena together:
the ebb and flow thing @ Long Ring Long Land and the Aqua Laguna @ W7.
Both of them seem to be linked together IMO. This might be far fetched, but even the KnockUp-Stream could be causing this other two phenomena. But its stated that the KnockUp-Stream happens once a month, the Aqua Laguna and the tides @ LRLL once a year iirc.
Though I sumhow doubt the SHs will travel to one of this planets. IMO there is only one moon, the other "bodies" are planets cause one them has its own "moon". Why I am convinced there is only moon that "shines" at night? Oda has put a lot of emphasis at the moon between Whiskey Peak and Drumm KD. Fans wanted to calculate the travel time of the SHs by studying the moon phases in certain panels back then (half moon, full moon, new moon, …)
I also don't think those other planets will be involved in OP. We have Enel and "his" moon to come back in the story, and I think that's all.
But it might be awesome if Oda's Mecha/Cyborg/robot story after OP will take place on one of those planets. @ least he said he'd love to draw a "Robot-Story" after OP is finished. I'd be patient there, it could take a while until that day...