I used this stacking software. Good thing about it, is that you need NOT install, you could just run the application. Also you could build time-lapse video too.I'm not sure about that but since I didn't have a stacking software (and my laptop didn't allow me to install one), so I've always gone for the long exposure technique.
Hey there is slight noise in the picture, i would suggest trying out the interval shots, you would be much more pleased with it.This is the most recent shot I've:
Also i had observed couple of times, when aeroplanes (at very high altitude) pass by, they make that light streaks in the sky, we could avoid that in stacking, by just fixing those frames.