Is Cosmos a part of Universe or both are same?

The cosmos is indeed a part of the universe. It is the studied, non-chaotic part though - the part that is not full of questions. It is what has been proven to be and what is known and is being studied. The universe is full of questions and chaos so that is considered to be a totally different thing.

Yes, though. The cosmos is in the universe. It has a sun, moon, the earth, planets, and stars. It makes sense, scientifically and mathematically. We find security in knowing these things that make sense.