Today is the first day of summer in the northern hemisphere.
The summer solstice is an astronomical term regarding the position of the sun in relation to the celestial equator. At the time of the summer solstice, Earth is at a point in its orbit where one hemisphere is most tilted towards the sun, causing the sun to appear at 23.45 degrees above the celestial equator, thus making its highest path across the sky. The summer solstice is the day of the year with the longest daylight period and hence the shortest night. This day usually occurs on June 21/June 22 in the northern hemisphere and on December 21/December 22 in the southern hemisphere. The actual date changes due to differences between the calendar year and the tropical year.
An excellent article on the meaning of St. John the Baptist's Day, now on June 24 but traditionally on the date of the summer solstice, can be found at Masonic Traveler's blog. The other St. John, the Evangelist, has a celebration day on the Winter Solstice.
A Mason should remember that many of the symbols of Freemasonry as well as of Christianity and other religions are reflections of what happens in the sky. The Saint John days mark the solstices. Man has added the spiritual symbolism. As above, so below.
Have a great summer!