1- I sat watching the rain.
2- I sat while I was watching the rain.
In the beginning, I thought the two sentences were the same, 1st one being a shortened form the 2nd one.
However, after I learnt about participles functioning as adverbs, I got confused and thought these sentences might not be the same.
So, here is what I now think that the sentences mean:
1- "I sat watching the rain". I think it means "I sat sometime in the past, and during this action of sitting, I watched the rain. In other words, the sentence can be an answer to the question: A: "How did you spend time when you sat?". B: I sat watching the rain.
2-"I sat while I was watching the rain.". I think it means I had been watching the rain for some time in a standing position, then I got tired, and I decided to sit down". It seems that the sentence can be an answer to the question: A:"When did you decide to sit?". B: I sat while I was watching the rain. So the sentence is not about how I spent time during the action of sitting, but when the action of sitting happened.
This is what I concluded. So, do these 2 sentences have the same meaning or do they emphasize different aspects?