Question

What is the difference between casual observers and scientific observers?

Answer 1

There are different types of observers. Casual observers differ from scientific observer. Seeing and observing are two different things. Not that everybody seeing is actually observing the thing.
A casual observer just sits back and watch for something to happen while a scientific observer comes up with some hypothesis to work on it. 

Answer 2

Observation is a central theme of scientific investigation. Scientists are usually expert observers, who have sharpened their senses when it comes to observing the external world and its phenomenon. The principal difference between a scientist and a casual observer is that the scientist ponder on his observation and analyse it critically to get more insight and information and the observation may lead to a totally new experimental project. While a causal observer will just observe and move on.