Wednesday, 8 October 2014

Why does Daylight Saving Time start so much later than it finishes ?


From looking at my earlier post on growlights, it again raises a question that been puzzling me for a long time.  

Take a look at this sunrise-sunset-daylight hours graph for our location. from that post, but with a few extra intercept lines I've added.  Click for a larger image....




British Summer Time (BST) will end this year on 25/26 October 2014, but it won't begin again until 28/29 March 2015.  

Why should this be ?


Daylight Saving Time across the world, for those countries in the northern hemisphere which adopt it, always ends around a full month after the autumnal equinox but doesn't begin again until a few days after the vernal (spring) equinox.  Logically, surely it should start a full month before the spring equinox.

At our location, the clocks go back at a time when there's less than 10 hours of daylight, but they don't advance again until a time when there's more than 12.  

Why ?

The same total hours of daylight prevailing on 26 October will be available again on or around 16 February 2015, although the clocks won't actually go forward until six weeks after that date.  That's the black line on the graph    

Equivalent sunrise time as at the end of BST is around the end of February 2015, that's the red line.    Equivalent sunset time is actually around the end of January 2015, the blue line.



adjusted to 'clock' time - so why isn't the RH side
more of a mirror image of the LH, about the winter solstice line

I appreciate that hours, minutes and seconds are only an arbitrary construct, as opposed to days which have a more physical determination, but as someone who very much prefers having the extra light available towards the end of the '...conventional...' day, and doesn't give a toss about what it's like in the early mornings, this is a mystery to me....

It seems that someone's stealing a whole month of lighter evenings from me - the bastards....



No comments:

Post a Comment