Subject: If plasma rarely forms on Earth, then how do we know that it exists?

Is plasma on the sun?  How do we know how hot the sun is if we have never been 
too close to it?  Is plasma a term for any "self-ionized" (is that the term?) 
substance above a certain temperature?  How do scientists create plasma?  I 
mean:  If they are heating it to such extreme temperatures, then how do they 
keep all surrounding materials from being melted? Thank you!  (sorry so many 
questions)

Re: If plasma rarely forms on Earth, then how do we know that it exists?