What time of day was this photo of the Washington Monument taken?
While writing this warm-up question, I came across the Sun or Moon Altitude/Azimuth Table page. Supply a location and a date and this page will tell you the angle of sun in the sky for any time of day. (Interesting side note: This photo of the Washington Monument could not have been taken between November and February because the sun never gets that high in the sky.)
I can already imagine all sorts of interesting extension problems based on this picture but for now I will keep it simple: my students need to practice the inverse trig functions.