Wednesday, February 07, 2007
Playing the angles
Speaking of slants of light, I’ve just seen a dramatic demonstration of the difference that the angle of incidence of the sun’s rays can make.
Back in elementary school when they explained why the Northern and Southern Hemispheres are colder in their winters two factors (as I recall) were cited:
1) the days are shorter, hence less overall sunlight
2) The sunlight strikes at a more oblique angle in winter, and is thus less powerful
#1 made perfect sense to me at the time, #2 not so much. Sunlight is sunlight, right?
Wrong. Certainly the ice on the sidewalks on Bigelow Street suggest there is a big difference. Bigelow runs more or less due North-South, up a hill that crests a block or so from my house. The North facing slope is fairly gentle, but just steep enough so that the sun’s rays on these low-angled winter days do not strike at all directly. This is in contrast to the steeper, south-facing slope, which meets the sun’s rays much more directly.
Despite the single and low double digit temperatures we’ve been having, the south-facing sidewalks melted clean in a day or so of sunshine after last Friday’s freezing rain. In contrast, you take your life in your feet walking on the north-facing sidewalks.
Back in elementary school when they explained why the Northern and Southern Hemispheres are colder in their winters two factors (as I recall) were cited:
1) the days are shorter, hence less overall sunlight
2) The sunlight strikes at a more oblique angle in winter, and is thus less powerful
#1 made perfect sense to me at the time, #2 not so much. Sunlight is sunlight, right?
Wrong. Certainly the ice on the sidewalks on Bigelow Street suggest there is a big difference. Bigelow runs more or less due North-South, up a hill that crests a block or so from my house. The North facing slope is fairly gentle, but just steep enough so that the sun’s rays on these low-angled winter days do not strike at all directly. This is in contrast to the steeper, south-facing slope, which meets the sun’s rays much more directly.
Despite the single and low double digit temperatures we’ve been having, the south-facing sidewalks melted clean in a day or so of sunshine after last Friday’s freezing rain. In contrast, you take your life in your feet walking on the north-facing sidewalks.
