Have you ever thought about the reason why, when we have in the northern countries, like in the USA and Canada, and the countries in Europe, cold winter season, and in South America, like in Argentina and Chile during the same time a warm summer? First, we need to remove the idea that it is because of the distance to the sun. Actually, yes, during the summer in the northern hemisphere we are closer to the sun, but it is not only the northern hemisphere that is closer to the sun, it is the whole Earth that is closer to the sun, during the summer in the north. But why is it summer in Argentina or in Australia, and in the Northern Hemisphere cold winter? It has to do with the inclination of the Earth axis of rotation. The axis of rotation will always point toward the northern star, Polaris. The Earth will not point to another star while revolving around the Sun. Because of that, the Sun will have an apparent motion between the southern hemisphere to the northern hemisphere passing the Equatorial line. The Sun describes a curve in the sky that is called the ecliptic, and when the ecliptic cuts the Equator on March 21, we call this point the Venal Equinox. This is the point when the day and the night have equal lengths. In the picture you can see how the sun is sending more warm rays to the north in June, and less to the south, and in December is the opposite. Just the axis of inclination!
AstroDidactics 