The
amount of sunshine we have depends on latitude
and how much cloud there is in the sky. In some of the world's deserts
the number of sunshine hours is very high, more than 3,600 hours each
year. In the Eastern Sahara desert, the sun is covered by clouds for
less than 100 hours a year. In Britain we have from 1,850 hours in
Southern England to 1,200 hours in North Scotland. There is usually
more sunshine where atmospheric pressure
is higher.
Hours
of sunshine are usually recorded on a simple machine called a parheliometer
also known as a Campbell-Stokes recorder. It works by using a glass
ball to focus the sunlight and rays onto a strip of card. As the sun
moves round during the day, the card is scorched creating a record
of how many sunshine hours there were.