Based on a talk that I gave to the Western Sydney Amateur Astronomy Group in September 2019 this video starts by canvasing the importance of recognizing the size of the astronomical objects that we view in our telescopes. It continues by showing how we can determine that size even if it is not quoted in our reference materials. It concludes by giving some examples of how knowing an object's size allows us to better understand its nature and how it fits into the larger scheme of things. (49 minutes)
It is recommended that you view it using the full-screen option.