Find the answer

We have started a competition today to see how many answers we can find out.

The first question is: Find an idiom meaning "not very frequently". In it, there is something that astronomers love.

2nd question: Who lives in 221B Baker St., London?

3rd question:
The sentence "May I have a large container of coffee?" is used as a memory aid for what?

4th question: What artist was the first one to have 20 million followers on Twitter? And 50 million?
5th question: Who was Frankenstein's mother?
6th question: Which is the nearest Star from the Earth?