What’s the difference between an equinox and a solstice?
An equinox is when the sun is visible above the horizon and below the horizon for equal time – 12 hours each. This corresponds to the sun being apparently directly overhead at noon on the equator. That happens on 21 March and 21 September.
A solstice is the longest or shortest day in each hemisphere of the earth, usually reckoned from the north (that’s us). So our winter solstice is 21 December (mid-winter’s day) and the summer solstice is on 21 June.
Signs of autumn in trees and plants
A familiar sign of autumn is leaves changing colour. This is a visible signal of the physical and chemical changes going on inside the plant as it prepares for winter.
Plants depend on light for photosynthesis to work, so that they can grow, change and reproduce. Less light and heat means that plants will either slow down their metabolisms as winter approaches, or if they are annual plants, it will be time to set seed and then die.
Many perennial plants will shed their leaves in winter and go into a state akin to hibernation in animals. If they shed their leaves – making them deciduous plants – they withdraw chemicals and nutrients from those leaves into the main body of the plant, such as the trunk and roots of a tree. This also rids them of products they will no longer need when they are resting, or that would even be harmful if kept in the main body of the plant. This is the equivalent of excretion or shedding of skin, fur or feathers in an animal.