@igwuisman - re: 'Today it is monday' is also correct right?
Hola igwuisman. Here is something to consider. I read somewhere that the word "it" does not exist in Spanish.
If that's the case why bother throwing "it" into the perfect correct English sentence, "Today is Monday."
Personally I'd say it is. There is nothing that you could add to the Spanish sentence to make the "it" correct (bad explanation but I hope you see what I mean), therefore "is" and "it is" are both acceptable English translations. However it may be something along the lines where technically "Today it is Monday" is not grammatically correct in English, although of course in every day life it's totally acceptable to say.
It's allowed to capitalize them, but it's not necessary I've seen capatalized and non-capatalized calendars Same goes for months