Have you had that feeling recently that the season has not so much shifted to autumn, as snapped?
There is a time each year when we get this feeling and its suddenness not purely psychological, it is because we witness the most dramatic changes in the Earth-Sun relationship at two times in the year: spring and autumn.
Some of the things that we tend to assume change gradually, actually don’t at all. On this blog I have mentioned that the bearing of sunrise and sunset change most dramatically at the equinoxes, in March and September, and briefly stand still at the solstices.
There are other things that change with varying speed over the course of the year and they follow a similar pattern. The length of day hovers at the same length at each solstice, but changes rapidly in spring and autumn. For example, in London (latitude is important),…
In this photo you can see the dew that the sun has not yet burnt off. The shadow itself is mostly moving right to left in this picture, leaving the thin band of wet wood in the shade all the time. This thin band is a rough east-west line at all times of the year, but quite an accurate one at times like this, close to the spring and autumnal equinoxes.