When the North Pole of the Earth is tilted toward the Sun, the South Pole is tilted away from the Sun. So, when it's summer in the northern hemisphere, it's winter in the southern hemisphere. For people living in the southern hemisphere, winter is approaching now and Christmas is a summer holiday!
What does the tilt of the Earth have to do with the seasons?
When the North Pole of the Earth is tilted toward the Sun, we receive more sunlight and the days are longer. In addition, the Sun rises higher in the sky, so the sunlight is more direct; that is, it comes down from above. This increases the amount of light that a given area on the Earth receives. More sunlight means more warmth, or summer.
When the North Pole is tilted away from the Sun, the days are shorter and the Sun does not rise as high in the sky. Less sunlight means less warmth, or winter.
Why are the hottest days after the first day of summer, and the coldest days after the first day of winter?
Even though there is more sunlight in the summer, it takes time to warm up the Earth and the atmosphere. This is just like heating up food in the oven – it doesn't happen in a second! So the heating and cooling effects from greater and lesser sunlight have a delay of almost two months. Hey, it's a big planet!
Doesn't the distance of the Earth from the Sun cause the seasons?
Many people think so, but this is not the main reason. The Earth is closest to the Sun in late December, but this is definitely not the warmest time of the year for people living in the northern hemisphere! It has more to do with the direction of the tilt of the Earth.