2012-11-13
Prickly lettuce is known to some of its navigating friends as the 'compass plant' and to its Roman friends as 'lactuca serriola'.
In truth it is only one of many plants with the compass plant nickname (Silphium laciniatum in the US is another one), but it has earned it.
In open ground, the leaves of the main stem are aligned north-south, offering the least surface area to the midday sun, but the maximum area to the weaker light of the start and end of the day. (This is a similar logic to the N-S alignment…
2012-10-02
If you stood on the same spot and took a photo of the sun every day during a year's worth of good weather, at exactly the same time each day...
...You might expect to see the sun moving up and down in the sky. But sideways?
In fact it would trace a figure of 8 in the sky. This shape is called an Analemma.
This has nothing to do with 'daylight saving' or any of the other artificial clock changes.
It is caused by two factors. The first is well known and understood by…
2009-11-06
On holiday I did try very hard not to think too much about navigation, but wherever I am I cannot resist checking that the sun is behaving itself appropriately considering my latitude and the season. At 7 degrees north, Phuket is in the northern hemisphere and the tropics and because the sun is now well south of the equator the short midday shadow is cast towards the north. Nearer June this same pencil would cast a shadow in the opposite direction at midday, to the south.This photo was actually taken eleven minutes after local midday, which is logical since it…
