Now that I looked into it, it seems like there is some mod (probably extra planets) with an orphaned moon, aka, a moon without a parent.
I couldn't reproduce it, but I think I fixed it.
=== 0.4.5 ===
- improved the environmental boost of isotope generators, fixes #33
- Upgraded to Galacticraft 1.7-3.0.12.488
- Fixed a bug where mothership data sometimes wouldn't be send to clients
- hopefully fixed the nullpointerexception in sky rendering
AmunRa-GC-0.4.5
I couldn't reproduce it, but I think I fixed it.
=== 0.4.5 ===
- improved the environmental boost of isotope generators, fixes #33
- Upgraded to Galacticraft 1.7-3.0.12.488
- Fixed a bug where mothership data sometimes wouldn't be send to clients
- hopefully fixed the nullpointerexception in sky rendering
AmunRa-GC-0.4.5