Sunday, 9 March 2014
12:37 PM
In the U.S. today, it's time for the semi-annual grump-fest about the changeover to Daylight Saving Time, aka DST. As we say around here, we "spring forward" an hour on the clocks, such that the first thing you do on Sunday morning is run around the house and slice an hour off your clock. You woke up at 9:00? Guess what, it's actually 10:00!
Some people don't understand why we do this, and lots of people don't like it, citing reasons from sleep deprivation to communism. It's true that DST doesn't make sense everywhere, and indeed, DST is not imposed everywhere. In the US, it's not uniform in Arizona, and Hawaii doesn't play at all.
Basically speaking, DST makes more sense the further north you go (or south, in the southern hemisphere), because it's an effort to even out, so to speak, the differences between the shortest and longest days. The closer you get to the equator, of course, the less of a difference there is, and at the equator, there is no difference (ok, only a very small difference) between the length of days on the solstices.
Ever since the beginning, offsetting the clock was proposed as a way to save energy (by Ben Franklin, who else, who calculated energy costs in terms of candles burned). The idea is to shift the bulk of daylight to the hours when people are most active.
Consider our latitude here in Seattle. Here's a graphical illustration of the times for sunrise and sunset at the solstices and with DST (not entirely to scale[1]):
Winter solstice[ 2] 
Summer solstice without DST
Summer solstice with DST
The general theory of DST is that more people are active on the evening side of the day than on the morning side. Or to use the numbers, more people are active at 9:09 pm than they are at 4:11 am. And being active, they need light, and why use energy (candles, electricity, whatever) when you could use daylight instead.
From the simple perspective of saving energy, it would theoretically be better to let areas impose DST that can actually benefit from it (Seattle, upper Alberta, whatever) and allow those areas that don't benefit from it (Key West, FL, Brownsville, TX) to give it a pass. But the benefits of having a standardized time system seem to (so far) outweigh the issues of imposing DST uniformly across the country.
Me, I'm not a morning person myself, so the longer the evening lasts, the happier I am. Daylight in the sky at 10:00pm? Fine by me. Sure, there's a hit today in terms of a lost hour, but that's like traveling one time zone, which is not considered that odious. And so tonight I'll be happy that there will be light in the sky well after 6:00pm.
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