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), the length of the day changes by only 2 minutes over the course of 10 days in late June. However, in late September the day shortens by 40 minutes in just 10 days.

The plants are very sensitive to this rapid change. The leaves on the trees begin to fall as the days shorten, or to be more precise, when the length of night increases. Since these are not steady, gradual changes, it is that much easier for nature to react at the right time. Autumn arrives with a loud rustle, if not a bang.

Happy New Year!

At times like this, I sometimes wonder what the Earth and Sun would say to each other if they could talk. They would watch us celebrating this annual moment at such an arbitrary time…

Sun: I could understand a party at either solstice…

Earth: Yes, or one at either equinox. Would make good sense…

Sun. Quite. But to pick a day about a week after one solstice…

Earth: Very strange.

Sun. Yes. They are a very strange lot.

In this picture of a beech tree in Wiltshire, we can see both moss and lichens thriving in the moist air close to the ground. Water evaporates constantly from the ground and moisture-loving organisms, including mosses, lichens and algae, will be found close to the ground regardless of aspect.

Direction can be found by looking for clues above this area or sometimes by getting to know the lichens in this low band itself. It is much more complex, and fun, detective work than simply thinking ‘green is north’.

On a different note, my book has just come out in the US!

As we approach the summer solstice the sun has so much north in it that no side of buildings, trees or other exposed areas will stay in the shade all day.

This is a northern roof getting a good late afternoon roasting. The moss, which in mid-winter is a plump dark green is in full retreat at this time of year. It is well-established and will survive until the sun starts moving south again in three weeks.

The last course stirred up some healthy discussion about the difference between the sun’s summer and winter arcs in the sky. The arcs are actually very similar, because they are parallel, but in our winter the arc is displaced to the south. However, the effect this has on shadows is more interesting and beguiling. The arc traced by shadows over the year are not parallel, but change quite significantly from summer to winter. This is because the sun rises north of us in summer and south of us in winter. The effect this has on shadows is quite counter-intuitive, but no less fascinating for it. The chalk line in this photo shows how the shadow from the edge of a flower tub moved this morning. In the summer it would have curved the other way and closer to the pot.