PUZZLE #3

The above pictures appear in an intentional order. 
Your task is to investigate each picture. 
For the photographs, you should determine:

1. The identity of the object in the picture

2. Why the object appears as it does

3. The significance of the object to the sequence above

For the central diagram, explain:

1. What the diagram represents.

2. How astronomers use this diagram.

3. Why I have placed the diagram sandwiched
between these two specific photographs.