Longer, colder, later days

Fieldfare 2302_filteredThe cemetery was full of fieldfares and goldfinches today. Fieldfares are energetic thrushes that come over from Scandinavia in the winter. In sunshine, and if you get close enough, they look lovely, with dark tails, grey heads and rumps, and a gold flecked breast. Their white underwings and pale lower bellies are their most noticeable characteristic though, together with their communal and restless habits.

It always feels good to see them, and with the bright twitter of the goldfinches and the warmth of the sun, the cemetery was a pleasant place to be today. The days are, after all, a little longer now. Sunrise is no earlier, though.

The reason for this is simple, but quite intriguing. The earth rotates once every twenty four hours. It also moves a little further along its orbit. Imagine the orbit of the earth as a line round the outside of a large clock face, and the earth itself as a watch moving round that line. The earth goes round the sun anti-clockwise, so as a day passes in December we can imagine it moving from the very bottom of the clock face to a position slightly further to the right, 1/365th to the right, in fact. As it does so, we can picture the rotation of the earth by imagining the second hand of the watch going all the way round once – backwards, or anti-clockwise, because the rotation of the earth, like its orbit, is anti-clockwise if you imagine seeing it from above the North pole.

However, when the second hand returns to the top of the watch face, because the watch has moved to a slightly different position on the edge of the clockface, the second hand is no longer pointing to the centre of the clock. It has to move a tiny bit further, past the 12 position, to point to the centre of the clock (representing the sun). It’s just a matter of a fifth of a second for the second hand, but for a point on the earth to turn past the position it was at the day before and again point at the sun takes about four minutes. It amounts to a whole day over the year.

That’s fine, though. We take our time from the sun, not the stars and just make our solar days longer than our stellar days. A solar day is 24 hours. A stellar day is 23 hours, 56 minutes and about 4 seconds.

However, the orbit of the earth isn’t circular, it’s elliptical or egg shaped. As a result the speed of the earth varies. When we’re closest to the sun we move a bit faster round the orbit, and when we’re further away, we go a little slower. Our orbit is only about 1 per cent away from being circular, but it’s enough to make a small difference. We’re closer to the sun in the winter, so we move slightly faster near the solstice. It’s enough to wipe out the slight gains in day length in the mornings. The earth still has to turn a little more to see the sun, and the latest sunrise doesn’t occur on 21st December, but a week of so later. Meanwhile sunset has been getting later for about three weeks now.

Sunrise is currently 8.13am. It won’t be as early as 8am until January 21st. But sunset, which is now about 15.59, will be 16.31 by then.

I like the thought of the earth spinning round its orbit, and the year slowly climbing out of darkness for us living at 52.2641 North.

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