Amateur Egghead - Why is psychology a science?

In this series, Amateur Egghead, I examine a range of different subjects on which I have no formal education or expertise of any kind. The opinions and thoughts within are my own and will likely piss a bunch of people off, mostly the ones who benefit from the things I talk about. -Ed.

It's difficult to start this without getting directly to the point; why is psychology still a science when the only thing we're learning about the human mind is all about the mechanics of the brain? The brain is the medium in which the "mind" resides, but it is not the mind itself without the person attached to it and the experiences that person has had. Science, as defined by Oxford, is:

"the intellectual and practical activity encompassing the systematic study of the structure and behavior of the physical and natural world through observation and experiment..."

The world, as we know it, is already astonishingly complex, so much so that we don't know more than a fraction of what constitutes knowledge, and we've been hammering away at this ever since we became sentient. Hell, we don't even really know when that happened (though there are some really good guesses out there). Our universe, that which we can perceive and surmise from observation, is immensely enormous and, from our perspective, has no end. How do we even fathom that concept?