eli5: Why does the longest day of the year not coincide with the hottest day of the year?


If it is the longest day because it gets the most sunlight why is it not the hottest on average? Why does it not correlate with the hottest day of the year?

In: Physics

Temperature depends on a number of factors beyond just the number of hours of sunlight on a particular day. Clear skies instead of clouds blocking the sunlight, weather patterns bringing in warm air masses from more southerly areas, a general lag as the landscape warms up from days and weeks of long days of sun.

The length of day does not affect the temperature of the surroundings. For relation – islands of Svalbard north of Norway has sunlight 24 hours a day from April to late August and the Average summer temperatures on Svalbard range from 3 to 7 °C . The temperature of the surroundings depends upon how the earth is tilted towards the sun, the altitude you are at on earth and how far away from the tropical oceanic currents you are located.

The ground and oceans can soak up tons of energy without showing much change, which means their temperature changes very, veeeeeeeeeery slowly. The fact that one day is longer than the others isn’t going to affect things much; it’s the cumulative effect of many, many, many energy-filled days that slowly makes days get hotter and hotter.

Same thing in the opposite direction: the coldest days of the year come some time after the shortest days of the year, because it takes a long time for the ground to give up the heat that it just soaked up all summer long.