The natural Navigation: The Right Course, Naturally

It is that time of year again. The sun and Jack Frost are working together to paint the land.

In this photo of a dog-mauled football, we are looking southeast. But why does the football’s shadow appear longer than the patch of frost? Surely, since the sun is rising it should be the other way round?

Useless clue: it doesn’t have anything to do with the dog, who wisely avoids footballs until they are well defrosted.

UPDATE: The patterns of frost we see as the day wears on are shaped by more than one factor.

The areas that have received direct sunlight will of course thaw faster than those that remain in the shade.

The colour of a surface has a huge effect too. Dark earth will thaw faster in the sun than light-coloured stone.

The wind also has a big impact on any day with a light breeze or…

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This photo of the roof of my home tells a story of the sun’s journey.

The morning shadow from the dormer window is retreating and the sun is reaching more of the roof with each minute. The frost from the night before is thawing in the warm light. It is also forming a very simple shadow compass. At this time of year the sun rises very close to east and the direction that the frost is retreating will be west to east. The protruding ‘nose’ of frost near the top of the roof can be joined to the jutting part of the shadow to form a near perfect west-east line.

This effect can be seen in so many places at this time of year, as we get closer to the spring equinox (20 March). It will also work close to the autumnal equinox (23 September this year), but not in…

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This picture was taken yesterday morning. The frost line on the top of my Land Rover runs close to a north-south line.

The morning sun has risen in the southeast and warmed the eastern driver’s side and southern rear of the car. The warming from the larger driver’s side is having a greater effect, which is why the main frost line is north-south.