[Marcus]

I think house rules can be great. But to me RAW says Assensing is the skill of learning thing from an aura, and perception is the skill you oppose sneak. So as far as I'm concerned while there must be different methods of sneaking in each condition, and likely different bonuses and penalties applicable, I still think sticking with RAW is the safer bet for rules logic. So we all know what's going on if we sit down at the same table at some convention.

[Stainless Steel Devil Rat]

I think house rules can be great. But to me RAW says Assensing is the skill of learning thing from an aura, and perception is the skill you oppose sneak. So as far as I'm concerned while there must be different methods of sneaking in each condition, and likely different bonuses and penalties applicable, I still think sticking with RAW is the safer bet for rules logic. So we all know what's going on if we sit down at the same table at some convention.

House rules?  Rolling Sneaking in place of Perception to spot someone using Sneaking is the actual example given on page 136.

[Youneko]

Wow thx for all your answers. It's much clearer now. One question remains though. As SunRunner said, astral perception has nothing to do with eyes, so indeed light has no effect on it. But if a building or a wall remains as shadow in Astral world, why not smoke?  Is it too thin that everyone could just astrally look through it?

[Stainless Steel Devil Rat]

Just as there are environmental factors that affect visibility on the physical plane, feel free to describe energies doing analogous things on the astral.  Even mundane smoke can appear to be dark and ominous on the astral, particularly if it's full of toxic chemicals.

[SunRunner]

When it come to inanimate objects its generally only long lasting ones that leave shadows on the Astral, Rain and Fog are temporary and dont last so they dont show up. Like I said in previous editions it was abundantly clear as they made special smoke grenades that explicitly said these effect astral perception and were developed because normal smoke grenades did nothing to astral perception. It was a specific combat tactic to have people go in dump a bunch of smoke grenades and then let the mages just pick the opposition off, it was causing the Corps no end of consternation in the Amazonia conflict as well as in England as well as they were having guerillas using this tactic chew up absolutely absurd amounts of military resources with it. Its why the decided it was worth dumping a billion nuyen into researching FAB grenades.

 I will admit that some of this is legacy stuff coming from previous editions but since I have seen nothing that even hints at changes to this I feel like its still legit. Lighting, Smoke, Fog, Rain and such from non magical sources have no effect on astral perception. Distance and distractions do effect assensing, you also have some unique things they call out like the fact that since your not using light in anway things like windows that are see through to normal sight are opaque to assensing.

At the end of the day every table is different, Play what works for you and your group.