I'm not Catholic, so forgive me, but I don't know much about Mass. I have a few questions:
How long does it last? For example, Santa Maria Maggiore and San Giovanni in Laterano apparently have Mass at 7, 8, 9, 10, 11, 12, and 18! About how long is each one?
Is tourism of any kind a definite no-no at a church during Mass? I mean, is it like I'm envisioning it? People sitting around worshipping while some guy in a baseball cap is in the background dropping coins into machines, spraying the wall with light, to stare at a painting? Or is it less intrusive than that?
I plan to visit a lot of churches in Rome, and I have found a decent list of Mass times at most of the ones I'll be going to. I just need to know how to approach Mass. Should I avoid those times entirely?