It's impossible to give a definitive percentage of Americans who know the sun is a star. There's no single, widely accepted survey that specifically asks this question.

However, we can infer some information:

* Basic Astronomy Knowledge: Most people learn in elementary school that the sun is a star.

* Scientific Literacy: Surveys on scientific literacy often show gaps in basic science knowledge among certain segments of the population.

* Misconceptions: Some people may hold misconceptions about the sun and stars.

Therefore, it's likely that a large majority of Americans know the sun is a star, but there may be a smaller percentage who are unsure or hold incorrect beliefs.

To get a more accurate answer, you would need to conduct a specific survey or study focusing on this question.