The Fastest Changing Day

Last week was Autumn Equinox, when day and night are twelve hours each.  Few people realize, though, it’s also the time when the day shortens most quickly.  Indeed, here in London, the day was a full 3 minutes and 54 seconds shorter on September 25st than it was the day before.  This change adds up: in the month around the equinox, our days will have shortened by almost two hours.  You can see this change here: 

 Length of Day (London, 2010)Daily Change in Day Length 

Even if we haven’t spent time on pondering the length of the day, subconsciously we all are aware that something has been going on recently.  Perhaps we have found ourselves thinking more urgently about all that lies before us.  During the lazy days around June’s summer solstice, when day length narrows by less than a second each day, time feels endless.  But now, when the sun creeps through our curtains a couple of minutes later each morning, we viscerally sense the passage of time.

It’s strange, isn’t it, that we always focus so much on the “equi” bit of the equinox, rather than on the more meaningful fact that the two equinoxes are the fastest changing days in the year.  It’s especially strange when we think how obsessed we are with rates of change in other arenas, like GDP growth, up-and-coming celebrities, and progress. 

Here we are, though, stuck on this spinning orb, each day tilting further away from the warming rays of the sun, further towards the cold dark emptiness at the end of solar system.  So we gather up a blanket against the coming chill, and ponder what it all means. 

 And just at that moment, a happy thought shines in:  from now on, at least, the days will no longer shorten as quickly. 

 – Liz

p.s.  Ok, I’m not an astronomer, and it be that the equinox is not actually the fastest-changing day, but a few days before/after it.

p.p.s. And for those of you in the Southern Hemisphere, enjoy the coming summer!