How do you, as a GM, describe Astral Space to your players? If a magic user goes into Astral Space and inspects a downtown club, what is it they see? How do you describe it to them?

usually I go over the difference in auras, the vibrancy of living things liek plants and animales, perhaps the occassional spirit, and the black void of cyberware. Emphasizing usually the difference in living things and technology. I generally describe things as brighter in the astral in a natural area, or darker in places like polluted cities. I also usually associate some sort of emotion the pc feels in charged areas like power sites and places w/ background counts.

You could also describe most of it is black and grey, with the living and magical as the only parts that have color.

yeah, but that's way to Rainbow Bright

There's some decent text on this in the astral space section of Street Magic.

I always start off with the emotional signature of the area. Whenever a player magician shifts into the astral, the first thing I hit them with is how the area feels, emotionally. Then I go on to describe how this manifests, usually in a visual metaphor (dark patches of astral space, vibrant and crackling auras, swirling clouds of mana) but not always. Sometimes I use other sensory metaphors, like scent or touch. I've described sections of astral space as feeling welcoming, like the warmth of a fireplace on an autumn day. Or smelling dead and lifeless, like a sharp tinge of ozone.

After I've conveyed the general emotional sense of the area, I go into further detail about astral shadows and auras.

Right, emotions are king. In the downtown club example you gave, the first thing an astral observer will notice is the joy, power, lust, zen, etc., of the mass of people packing the dance floor. Whatever tone the undoubtedly skilled DJ wants to imbue in the throng of clubgoers engrossed in his music will permeate the immediate astral area. If people are having a really amazing experience, where they lose their minds and transcend their normal range of emotion, you're going to get background count.

The building itself will be gray and shadowy, but the people who inhabit it will pass on some of their light and color to the area. Under the right circumstances, people can pass on an emotional residue to their surroundings which the astral observer can pick up on. This can manifest as a bit of color or something.

Astral observers are really sensitive to emotions. In fact when you consider the nature of astral space, I find it amazing the hermetic tradition exists since the workings of magic seem to lend themselves so much easier to someone working from their gut... artists and others with high intuition.

lol... maybe im more about the music

I;m reminded of the Jay-Z video 99' problems at the end when they swith the lens to thermographic vision. Everything else is gray except the people who represent differant colors to include of of there emotions. if there are a gorup of people it makes it hard to single out a particular person because all you see is waves of emotion unless you know there silouette or general emotional state.