Expert: Harry Hayfield - 9/28/2010

Question
Hey Harry,

        Quick bit of context. I'm a screenwriter currently writing a detective character who discovers a photograph (or perhaps a painting.... undecided) which he then uses to trace a missing person.

My question is just how much information can be gleaned from an outside photo or painting with regards light source. As a for instance-

1. Can anything more than time of day be worked out by angle? Or darkness values? Or length of shadow?

2. Could season or even month info be gleaned from position of sun. Or moon. or angle/direction of shadows?

The photo/painting is of a building with setting sun glinting off the rooftop. I've already worked out that means he knows it was painted/taken from an easterly position facing West.

I'm basically looking for anything else that can be worked out from shadow and light? Any clues that can aid the characters investigation.

Thankin' you in advance

Alex


Answer
Indeed, all that information would be used to calculate time and season. If I may elaborate (using a possible scene that you could use)

"There's a clue in this picture, I just know it. Come on, concentrate! The sun's glinting off that rooftop and I know that the picture was taken looking west so...that's it. That's the clue I've been looking for. That's a picture of the Chrysler Building which I know is 1,047 ft and that shadow is 524ft long. That means I can calculate the angle of the sun and cross reference that with data about the height of the sun at a certain time. This will help me find that person!"

Using basic trig it is possible to calculate the angle of the sun based on the length of the shadow of an object (if you know the height of the object creating the shadow) and then it is possible to collerate that information with published data on the height of the sun at any time on a given day.