I want to study astrophysics in my free time.

 I like studying physics. I study physics everyday. I am very interested in quantum mechanics and I am going to become a physicist studying and experimenting spintronics in the future. 

 I also like astrophysics. I have never studied astrophysics before but I am interested in the field. We can see billions of stars in the sky and these stars' moving and other behavior can be described with astrophysics. Don't you think it is a glorious thing? 

My major is solid state physics, and that is definitely wonderful field (this is the reason why I study electron, spin, orbital momentum and etc. everyday.)

In short, I want to study astrophysics as a hobby in the future.