At two points throughout the year, the tilt of the Earth’s axis reaches its maximum angle compared to the Sun, and begins to move back the other direction. This usually happens around June 21st and December 21st. These days are known as solstices. On these solstices, the rays of the Sun shine directly on one of the two Tropics. During the June Solstice the rays of the Sun shine directly on the Tropic of Cancer. During the December Solstice the Sun’s rays shine on the Tropic of Capricorn.
As the Earth moves around its orbit, it reaches two points during the year where the tilt of its axis causes it to be straight relative to the Sun. These days are known as equinoxes. During these equinoxes the rays of the Sun shine directly on the equator. This happens on approximately March 20th and September 22nd.