We say we are using a ‘frost compass’ when we find direction by looking at frost patterns.
We can navigate using the sun, because it follows predictable and dependable patterns as it moves over the sky.
The sun warms the land. Frost in sunlight thaws more quickly than frost in the shade. This creates areas where there is no frost and areas where there is frost (known as frost shadows).
Here is a sublime example of a frost shadow:
If we put these simple facts together it means we can draw a line from frost patterns back to the sun and this gives us a strong clue to direction.
Let’s start with nice simple patterns close to home. We should expect big differences on the north and south side of a building:
The patterns we find on the east and west side of buildings are often more intricate and depend on angles and time of day.
Notice how in the two pictures above, the sun has managed to melt some of the frost, but not all of it. In the first of these two, we are looking west and the sun is to our left; vice versa for the second image.
Now, let’s look at some variations.
The Many Patterns of Frost
In the picture above we are looking North in the afternoon. There is a ‘frost shadow’ where a house has kept part of the lawn in shade all day. On the left there is another frost shadow, where a hedge has down the same thing. The green line between them shows where the midday sun has managed to get between the building and the hedge to thaw that part of the grass.
In the picture above we can see how the effect can build over several days. The areas that never get sunlight end up with multiple layers of frost, leading to deeper frost and shades of white.
And gradient plays a massive part. In the photo above we are looking east over some grass with a very gentle rise in it. This is the same effect as we saw in the roof, only this time on a near-level piece of ground. A tiny gradient (like a flattened roof) is enough to create a sunny south-facing green area and a whiter cold north-facing area.
Once you’ve practiced looking for these effects close to home, you’ll start to spot them everywhere.
Which way are we looking in the picture below? Answer at the bottom.
The ground to the left of this picture has a deeper white colour, the result of several nights of deep frost.
The right side of the path has a frost, but it is a weaker one, because it has thawed each day.
We get the deeper frost on the south side of the track, because the shadows and sun are on that side.
We are looking WEST.
Here we can see why there is the colour difference:
Which way are we looking in the picture below? Answer below.
In the photo above we are looking South-East.
A deep frost has formed in the shade of the forest, on its northern side.
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