Sunlight streaming through the window Shines on Christmas cards and books, ornaments my sewing kit. As the sun rises it also travels south in the sky in winter. Then in the afternoon it appears to move downwards and West. So because of the way the earth is tipped on its axis the position on the sky moves in arcs that tip further south in the winter and further north in summer. So the sun appears overhead eventually.

If the Earth was rotating on a vertical axis at 90° to the plane of the solar system, then day length would stay the same all over the world. 12 hours day and 12 hours night. There would be no seasons. There would probably be no poles as all parts of the earth would receive the same amount of heat from the sun.

Instead the tip of the axis means that the day length changes over the years. So at the solstices the earth has turned to have its poles either closest or furthest apart from the sun. It’s also complicated by the earth travelling in an elliptical orbit round the sun. In the summer in the North of the world the sun is actually slightly further away from the earth than in the winter.

Anyway enough of celestial mechanics. Don’t get me started on the moon! Happy Boxing day. X