The Tilt Of The Earth's Axis & The Seasons

If the axis of Earth was perpendicular to the plane of its orbit (and the direction of incoming rays of sunlight), then the radioactive energy flux would drop as the cosine of latitude as we move from equator to pole. However, as seen in
Figure 6, the Earth axis tilts at an angle of 23.5° with respect to its plane of orbit, pointing towards a fix point in space as it travels around the sun. Once a year, on the Summer Solstice (on or about the 21st of June), the North Pole points directly towards the Sun and the South Pole is entirely hidden from the incoming radiation. Half a year from that day, on the Winter Solstice (on or about the 21st of December) the North Pole points away from the Sun and does not receive any sunlight while the South Pole receives 24 hours of continued sunlight. During Solstices, incoming radiation is perpendicular to the Earth surface on either the latitude of Cancer or the latitude of Capricorn, 23.5° north or south of the equator, depending on whether it is summer or winter in the Northern Hemisphere, respectively.

During the spring and fall (on the Equinox days, the 21st of March and 23rd of September) the Earth's axis tilts in parallel to the Sun and both Polar Regions get the same amount of light. At that time the radiation is largest at the true equator.