Most people use a telephone.
Step 1: you call someone to do it for you
a gimp
Call the place and ask
It's called getting your PhD.
"Let's call it a day?" is said when someone suggests packing up working for the day and going home.
By finding a place where someone can hire them to work.
Planetarium
You should call your manager or supervisor. It is not your responsibility to cover for someone else. You could also call in someone else in the position to see if they wanted to come in.
A person who passes by a place or incident is often simply called an observer or passerby.
If you have the power (i.e. being an owner or boss of a place) then yes.
Someone is an indefinite pronoun, a word that takes the place of a noun for an unknown or unnamed person. Example: Someone will call you when your order comes in.
A mechanical working model of the solar system is called an orrery. Many observatories have them, as do thousands of individuals.