I’ve got a project for someone.  You’ll need a camera and a computer, and some programming skills, and a web site that can host about 400 photos.

A couple weeks ago I was driving from my office to downtown Bellevue shortly after sunset.  The sky and the buildings looked like a typical autumn evening around here.  And that got me wondering what exactly it was, other than my knowledge of the calendar and my view of the trees, that made me think it’s an autumn evening as opposed to any other season?  I figured it was probably something about the angle or quality of the light that did it, but since the sun had crossed the horizon a little while earlier it wasn’t direct light or shadows.  Whatever it was, it looked cold.  I was glad I had a warm car and gloves.

We take a lot of very subtle cues from the environment that help us determine where we are in the daily or yearly cycle.  Go take a nap in the park on some nice summer day.  When you wake up, don’t look at your watch, just look around you at the shadows.  Odds are, you’ll probably have a rough idea of how long you were napping based on how they’ve changed.  Most of us don’t deliberately try to learn this, but you see the world every day, and after several years of living year-round in the same place, you get an innate feeling for when the leaves will sprout or change color, and how long it takes shadows to crawl across the floor.

I didn’t think about this very much until about ten years ago, when I visited South Africa for a week in June.  We got off the plane around 10 a.m. local time, but as we drove out of the city into the more rural areas, something felt really off.  Logically I knew it was morning, but my brain was convinced it was six or eight hours later.  I’m sure part of it was jet lag and the unfamiliar countryside, but there was something different about the way the light was hitting in the Southern Hemisphere that just looked out of whack.  I was aware that we were in a different season and therefore the length of the days and nights would not be the same as what I’d just traveled from.  But I couldn’t figure out why I’d have the sensation that east and west were opposite of what I was used to, or that we were a couple hours away from sunset rather than a couple hours past sunrise.  Over the years since that visit, I’ve tried a couple times to work out the geometry of the problem in my head but I only end up confusing myself, convinced both ways at once.

Anyway, the project.  Set up a camera pointed at a fixed location outside–preferably one without too many natural cues like trees and grass.  Find the sunset tables for the next 12 months.  Program your camera to take a picture a set interval after sunset every day, say something in the range of 15 to 30 minutes.  It needs to be after sunset so that ambient light is reflected rather than direct, but I think the priciple would also work if you take a picture a set number of minutes prior to sunrise, just as long as the sun is below the horizon.  Then upload that daily picture to a web site where I (and anyone else who’s curious) can compare pictures taken several weeks or months apart, and see whether there really is a difference between the look of a spring evening and a fall evening.