In my five and half months of living above 62 degrees north latitude I’ve learned many things regarding the effects that this location imposes upon daily life. Without question the meteorological effects are more extreme and definitely more pronounced but so are other aspects such as light. I recently experienced my first Winter Solstice above 62 degrees north latitude and it was definitely different from all those I experienced in the lower 48; the day was very short with not much light and a lot of darkness. Now in the lower 48 I remember seeing almost no perceptible shift in the daylight until we were well into February and I am a sky watcher and hence more aware of such nuances. However, up here, within two weeks I could definitely tell the daylight was increasing and that has continued to this writing. We are currently adding 3 minutes and 30 seconds of daylight per day and it is very noticeable. Yet this figure is the same regardless of where one is on the earth – okay, if you’re in the southern hemisphere then the daylight is decreasing but it’s still doing so by this same amount – so why is it so noticeable at higher latitudes yet becomes harder and harder to discern as one approaches the equator..?
My suspicion is it’s based upon the geometry of a sphere and one that’s tilted at roughly 23 degrees to the vertical in conjunction with the atmosphere. I’ve never been good with mathematics in general and geometry in particular but I can imagine the earth as a roughly spherical object (if ya want to get picky I guess it’s closer to an egg shape…) tilted 23 degrees off the vertical axis and not just spinning but also orbiting the sun. It’s the tilt that gives the earth its seasons; as it orbits the sun one of the two hemispheres (northern or southern) will at one point be closer to the sun – and hence have ‘summer’ – and at the opposite position in its orbit be tilted away from the sun and hence experience ‘winter’. So far, so good… Now, its known that the thickness of the atmosphere varies with location; it is thickest at the equator and slowly decreases as one moves towards the poles This means that sunlight reaching the earth has to travel through different thicknesses of atmosphere to reach the surface. The more atmosphere the light travels through the more diffuse it becomes; its scattered by all the various molecules in the atmosphere. Therefore at lower latitudes incoming light travels through more atmosphere and is more scattered and hence more diffuse and so would appear to be ‘weaker’ than light striking the higher latitudes. This could well account for the perceived slower shift to increasing daylight in the lower 48 as to up here; the more diffuse and ‘weaker’ light requires more time to finally begin to show a change where as in the higher latitudes the light is not scattered and diffused as much so smaller changes are more easily perceived by our eyes. This also explains that phenomena of ‘flat light’ that photographers often speak to; it’s this same sharper, stronger light that traveled through less atmosphere.
Or at least this all sounds well and good; an interesting test would be to find a planet with the same tilt but no atmosphere to use as a baseline. If this summation is correct the perceived increase/decrease of light on the planet without an atmosphere would appear to be the same regardless of one’s latitude. It’s these kinds of situations I enjoy investigating; to me they are not immediately obvious yet they are undeniable. Without question the less thick atmosphere produces some other effects at the higher latitudes; I suspect this is the reason I see such amazing barometric pressure swings up here. Just this past Monday I saw a pressure reading of 28.88″ Hg (978.26 Mb) which is extremely low and would be something one might see in the eye of a medium strength hurricane in the lower 48 yet up here it was just low pressure; we did see a bit of snow along with it but no winds or other extreme weather.
It’s an interesting experience living in the higher latitudes; it makes me wonder what it would be like living at 80 degrees north latitude if not higher..? I suspect I’ll never know as the farthest north piece of Alaska is around 71.5 degrees north latitude. Still and all its fun to wonder…