Nebulas are interstellar collections of ionized gas covering vast areas with a fog which is difficult to penetrate with conventional sensors. This causes the following effects:
Hide ships and planets: Each point of nebula has a visibility factor depending on the level of density. Ships and planets will only be visible at this range.
All cloaking ships except the advanced cloaking Resolute and Darkwing which end their movement inside of a nebula will be decloaked after movement. Ships which start their movement inside of a nebula are decloaked at the beginning of the turn.
Minefields and web minefields which are overlapping a nebula suffer from a 3X higher minefield decay rate.
Cobol Ramscoop does not work (if ending movement inside a nebula).
Planets inside Nebulas are 10 times more likely to experience a small meteor shower.
Bioscanners and sensor scans do not work on planets inside of a nebula except for the Pawn Class Baseship (Robots).
Ionstorms which encounter a nebula have their voltage reduced by the nebula intensity each turn they touch the nebula.
All native life on planets inside a nebula with visibility less than 50ly may be taxed higher than the normal rate before becoming angry. Since these natives have never seen the stars the arrival of aliens causes the entire population to go into a religious fervor.
The Cyborg B41 Explorer and the Birdman Swift Heart Class scount are equipped with a Neb Scanner which will automatically detect planets and ships inside a nebula up to 100 light years away regardless of the nebula density.