The insolation of a place is the power of sunlight received by a horizontal square metre at the top of the atmosphere above it. Averaged over the twenty-four hours of a day, it is the daily-mean insolation; averaged over a year, the annual-mean insolation; both are measured in .
উদাহরণ
Example 3.4 (The pole in June)
At the June solstice the Sun stands above the horizon of the North Pole all day long. The daily-mean insolation there is ; over twenty-four hours this is , per square metre. On the same day the equator receives a daily mean of , or per square metre: the Sun rises higher there at noon, but it is down for twelve hours.