UK seasonal day length

The difference is latitude on a tilted axis, not distance to the Sun. Earth’s orbit is only slightly elliptical. Perihelion — nearest the Sun — falls in early January, during northern winter. If distance caused seasons, London and Sydney would share summer. They do not.

At 51.5°N, London’s noon solar altitude on the December solstice is about 15°. On the June solstice it is about 62°. Day length swings from under eight hours to about 16.5. Walk north to Lerwick, near 60°N, and the December day falls below six hours; June barely gets dark. The same geometry, stretched.

A-level and AP students can treat this as insolation: the solar constant is the same. Incidence angle and duration are not. The energy received on a square metre of playground in December is a sliver of the June figure, even under a clear sky. UK solar farms know this in their yield curves. Field teachers know it in the last period on a winter Friday.

Compare Miami, near 26°N. December noon altitude stays above 40°. The day shortens by a couple of hours, not eight. Growers in the Central Valley care about hours above a useful incidence angle — the same number UK horticulture cares about under glass. Tilt, not orbital distance, is why a Californian December is not a British one.

Classroom move: freeze the seasons lab on 21 December. Read London’s day length, then Sydney’s. Ask which hemisphere is leaning toward the Sun before you reveal the tilt callout. Then scrub to June. The terminator walk is the whole argument.