The clearest ghost I have seen

I have one really clear experience with a ghost. It was the ghost of my grandmother. Several years after my grandmother died, I was visiting my parents. My room had been made into a home office, so they had made "grandma's room" into the guest room. I had stayed in that room numerous times before my ghost experience. In the middle of the night, I was awakened by the rocking chair rocking with no one in it, this chair makes a distinctive squeak when it rocks. As I looked at the chair, slowly the form of my grandma became visible. She was crocheting and rocking in the chair. She seemed to notice me looking at her, she turned her head and smiled at me and then went back to her crocheting. She was visible for what seemed to be a long time, but it was probably only a minute or so.
When I talked to my mom later she said there are times when she heard the chair rocking, but had never seen anything. I haven't seen her again in that room, although I have seen the chair rock 3 other times in the middle of the night. Ever since then I always say hi to her when I come to stay in "her" room, and say "I hope you don't mind if I use your room for a few days".
What is also strange is that occassionally my dog will go and sit infront of that chair as if someone is sitting in it, and he is expecting a treat from that person.