When the Earth's Northern Hemisphere is tilted towards the Sun, the Sun's rays are more concentrated on that part of the Earth. This results in longer days and warmer weather in the Northern Hemisphere. At the same time, the Southern Hemisphere is tilted away from the Sun, so the days are shorter and the weather is cooler. This period of time is called summer in the Northern Hemisphere and winter in the Southern Hemisphere.
When the Earth's Northern Hemisphere is tilted away from the Sun, the Sun's rays are more concentrated on the Southern Hemisphere. This results in longer days and warmer weather in the Southern Hemisphere. At the same time, the Northern Hemisphere is tilted towards the Sun, so the days are shorter and the weather is cooler. This period of time is called winter in the Northern Hemisphere and summer in the Southern Hemisphere.
Twice a year, the Earth's axis is not tilted towards or away from the Sun. These two times are called the equinoxes. During the equinoxes, the days and nights are of equal length all over the world. This occurs on March 21 and September 21 each year.
The solstices are the two times of year when the Earth's axis is tilted the most towards or away from the Sun. The summer solstice occurs on June 21 each year, and the winter solstice occurs on December 21 each year. At the summer solstice, the Northern Hemisphere is tilted the most towards the Sun, so the days are the longest and the nights are the shortest. At the winter solstice, the Northern Hemisphere is tilted the most away from the Sun, so the days are the shortest and the nights are the longest.