Today is June 21, the celebration of the summer solstice in the northern hemisphere. In England, Stonehenge has been opened to the public for celebration of the solar event.
A solstice occurs when the rays of the sun directly strike one of the two tropical latitude lines. The northern line is the Tropic of Cancer and the southern line is the Tropic of Capricorn (both titles of Henry Miller books, by the way).
By the way, as it stands today, the Tropic of Cancer should be renamed the Tropic of Taurus and the Tropic of Capricorn should be renamed Tropic of Sagittarius. This is due to the precession of the equinoxes.
To understand the precession of the equinoxes, it's important to understand the fact that the Earth wobbles slightly as it spins. Therefore, the northern tip of the axis creates a small circle in the night sky--just like a wobbling gyroscope.
As a result, the equinoxes and solstices go through a complete cycle ~ every 26,000 years. For more on this topic, click here.
Despite the name inaccuracies, June 21 marks the beginning of summer in the northern hemisphere and simultaneously heralds the beginning of winter in the southern hemisphere. In 2006, the solstice begins June 21, at 8:26 a.m. EDT.