You can never make assumptions about who someone is when you haven't interacted socially. That smacks of judging a book by its cover. Just because someone looks straight-laced doesn't mean that they aren't up for a good time. Just give them an invitation and see how they react. Chances are they're going to surprise you. This is their way of showing you that they trust you, so take it as a compliment. Go out and have a good time!
Your birth chart is a map of the sky at the moment you were born. Download the Sun Signs app to find out how the planets’ positions influence your life.