I'm struggling to invision what you see on the astral plane and how to describe it to the players.

You can see aura's i get that.
You get photo negatives of anything non living.

Can you see through objects that arn't living i.e. wall's. Could you use astral perception as a heat sensor to see what's on the other side of a wall?

Is what ever is residing on the astral brighter?
Can you confuse an astral denzien (spirit) with someone who's astraly percieving.?
Can you see the other meta planes from astral?

Overall I'm just a tad confused and could do with some advice on how to convey to the players what's happening on the astral.

You can't see through much of anything. Even clear glass blocks your astral vision. Things that are astrally active are much brighter. Auras, spells, spirits, foci.

I think it would be hard to confuse an astrally perceiving or even projecting human with a spirit. You might need like 1 hit on an assensing test, but most GMs are just going to tell you without rolling it.

Remember that astral perception actually covers all the senses, not just vision. It's just easiest to describe it in terms of vision. But, you can use hearing & touch as allegories for it as well.

Some of the older books, like the Grimoire or SR3 had pretty good descriptions of Astral Space - one of the weaknesses of the SR4 book, in my opinion.

I generally hold that there are four categories of things in Astral space that a mage can see and distinguish automatically.
1. Dead things. Buildings, walls, cars - anything inorganic or dead. Appears black and is solid, no matter if it is translucent or transparent in physical space.
2. Alive things. People, animals, plants. Nice soft glow. Plants are fairly dim, but visible. Note: the planet appears to be alive.
3. Astrally active things. Dual natured critters, manifest spirits, sustained/quickened spells, active foci, perceiving mages, projecting mages etc.
4. Purely astral things. Projecting mages and spirits can be quickly identified as such because they don't have a physical form corresponding to their astral aura.

The various different categories of astrally active things can be distinguished with a Perception or Assensing test.

And, for what it's worth, I hold that Masking allows you to shift your appearance in Astral Space up or down one category, as well as outright concealing an aura. E.g. When astrally perceiving, you can appear to be a plane normal person.

It gets tricky is with invisibility spells. The spell description says it doesn't conceal the subject's aura, but having a sustained spell on the target would glow like a beacon in astral space...and make the spell pretty much useless against magical security. So I assume, that the spell also works on the astral plane.

It's not tricky. Invisibility is for physical only; yes, it's worthless against magical security.

My question has always been if things like Astral Cloak help you hide an invisibility spell. I think probably yes.

The Concealment spirit power works on both the Physical and Astral planes, as does the Infiltration skill, that should be more than enough to get by patrolling spirits.

No, you can't see through walls, glass, or anything else (you know, except air). You might however be able to see part of an aura if you are looking at a very thin wall and someone is leaning against it, similar to what you would get with thermal vision and noticing a hot spot on the wall (Except you know it isn't a fridge)
Yes, things residing on the astral are brighter, you could only confuse a spirit with a person if you were really really clueless about astral (like no astral perception ranks, or maybe a glitch) unless someone is using masking to make their aura look like that of a spirit purposefully. You can't see the other metaplanes.

The astral is often described as being very colorful and vibrant in regards to astral things, and very dull, grey, blurry in regards to things that aren't. If you've seen Sin City, think of how it is mostly black and white, but a few special things have color. Throw in a blur effect for the black and white stuff and you have a decent idea of what the astral might look like.

That's great guy's thanks for clueing me up.

Karoline I'm going too steal the Sin City analogy, that's brilliant.

You're welcome, and thanks

While astral sense is often communicated in visual terms, it is not sight. It's a different sense.

Unfortunately, it's indescribable, so we rely on sight. The closest thing is the multi-sense sculpted VR of the Matrix, but even that…

This to me is the single biggest problem with Astral Perception and undoubtedly the biggest cause of confusion for new players. IMO they should just drop all the silly nonsense and just make it a type of vision like Thermographic or Night Vision. That simple little change would eliminate virtually all confusion and debate about how Astral Perception works and what can be "seen".

I don't see that there's even another choice (that is, besides sight-like). We talk about the 'sense' being blocked by glass and walls, and other auras, so it's more like vision than any other sense (for humans). It's even more like vision than something like air-traffic radar, because you do get a '3D' impression of the scene around you (unlike hearing or smell).

For some reason, I always thought it would look like Eagle Vision from Assassin's Creed.

I need to sit down and read this section more fully (heck, I need to find the section(s)), but I just want to make sure I'm getting this.

You can't perceive though walls but you can walk through them?

Or am I doing some apples and oranges bit?

Correct.

Unless they're warded.

What is Astral Cloak?

Invisibility for the astral plane? Don't really know, just guessing.

The problem is. If you try to walk through a wall without knowing what might be on the other side you may get screwed by:

A- Someone waiting to ambush you.
B- an astral barrier that might kill you if you were moving fast.