"It is a long night."
Translation:Estas longa nokto.
"Leaving out ĝi" is the wrong way to look at it. The real trick is learning why English adds "it" or "there" in so many places where there isn't an actual it or an actual there.
- It's hot today. What's hot today?
- There's a jug of milk in the fridge. Where's a jug of milk in the fridge?
- It's a long night. What's a long night?
- It's not that easy being green. What's not that easy being green?
Because there's no "actual it" or "actual there", all these sentences would start with "Estas..." in Esperanto.