SCIENCE NEWS

Isn’t it getting dark early these days? Yes, because we’ve just passed the autumn equinox, TUPNews can report. September 22 was the autumn equinox, the point at which, traditionally, day and night are the same length. I say traditionally because it’s not strictly true. These days the equinox is all about celestial geometry – the point at which the centre of the sun intersects the celestial equator (that is, the earth’s equator projected theoretically into space).

On the equinox, the day is in fact still longer than the night, because of the refraction of the sun’s rays through the earth’s atmosphere. Also, sunrise and sunset occur when the sun’s outer edge (trailing limb, to use the technical term) disappears under the horizon, rather than the point at which the centre of the sun intersects the horizon. This adds about two minutes of sunlight to the day. The point at which day and night are actually equal was in fact yesterday, September 25, TUPNews can reveal. In London, the sun rose at 5:51am and set at 5.51pm.

Isn’t it getting darker fast? Yes, to a certain extent, TUPNews can report. I was wondering just the other day whether the day gets shorter at a steady rate, or whether there is any parabola action involved that might see night make its biggest gains over a short period of time. It’s a little of both: from August on to mid-November, the amount of evening light falls a pretty steady rate of two minutes per day (so four minutes for the whole day if you count the lost morning light). From mid to late November, this falls sharply to a rate of one minute per day, before suddenly bottoming out in December. Between December 1 and 23, sunset stays within a four minute range (3.54pm-3.51pm for London). By late January, it’s back to a rate of 2 minutes more evening light a day.

I’ve focused on the loss of evening light, as I don’t consider the loss of morning light to be a real loss. Getting up while it’s still dark makes you feel like you’re going on holiday, which is great. Also my morning jog takes me down Landells Road in East Dulwich, which affords an excellent view of Canary Wharf. The Wharf is always fantastic, but seeing it still lit up first thing in the morning is sublime.