When is the duration of insolation the least?

The duration of insolation, or the amount of solar radiation received at a given surface area, is least during winter, especially at higher latitudes. This is primarily due to the tilt of the Earth's axis and its orbit around the Sun. During winter, the hemisphere tilted away from the Sun experiences shorter days and lower angles of sunlight, resulting in less time for solar radiation to reach the surface.

At this time, the sun follows a lower trajectory across the sky, and the daylight hours are significantly reduced, leading to a shorter duration of insolation compared to other times of the year. In contrast, during the equinoxes, the duration of insolation is relatively equal across the globe, and summer sees longer daylight hours and increased insolation. Noon time typically provides the most intense sunlight but still does not affect the overall duration of insolation for the day. Hence, winter indeed represents the point in a year with the least duration of insolation.