I had hoped to be able to take some photograph of the trees in autumnal colours, but the weather remained cloudy for much of the afternoon, with occasional spots of rain. Then, towards dusk, the skies began to clear and this fine rainbow appeared, remaining visible for around twenty minutes.
Images
Autumn equinox
The phenomenon is neatly demonstrated by Stellarium. The Sun is at the point where the ecliptic intersects with the celestial equator. Hence day and night are of equal length. Tomorrow and for the next six months, the Sun will be south of the equator and the nights will be longer than the days.
