This is a great example of why I got the FM3a. Ok, it's not actually such a great example. It was a bit over exposed. The film is a cheap brand so it's grainy. But I still like it.
This photo is a 20 minutes long exposure. On digital this would require heavy noise reduction, usually something called dark frame subtraction. Mechanical cameras like the FM3a are great for long exposure shooting as you don't need the battery to do any shooting.