MELBOURNE, Florida -- The Summer Solstice will occur on June 21, 2015 at 12:38 Eastern Daylight Time (16:38 Universal Time) which also happens to fall on Father's Day this year.
A Summer Solstice can occur on June 20, 21, or 22, depending on calendar events such as leap year and when the Solstice begins relative to Coordinated Universal Time. In the United States, Father's Day always falls on the third Sunday in June, so occasionally the two events occur on the same date. The last time the Summer Solstice fell on Father's Day was in 2009 and will not happen again until 2026.
What is the Summer Solstice?
The Summer Solstice is the shortest night and longest day of the year on Earth's northern hemisphere for locations like Melbourne, Florida, but the reverse in the southern hemisphere for locations like Melbourne, Australia. During the Summer Solstice, the Sun sits above the Tropic of Cancer, spreading more sunlight in the north and turning the tables on the south.
Several celebrations going back to primitive times center around the Summer Solstice because the apparent change in location of the Sun and Moon marks important dates for hunting and farming as evidenced by the astronomic architectural designs at Stonehenge in England and Mayan and Aztec pyramids in Central and South America.
However, it is not the Sun that is moving north or south through the seasons, but a change in the orientation and angles between the Earth and its nearest star. The axis of the Earth is tilted 23.5 degrees relative to the Sun and the ecliptic plane. The axis is tilted away from the Sun at the December solstice and toward the Sun at the June solstice, spreading more and less light on each hemisphere. At the equinoxes, the tilt is at a right angle to the Sun and the light is spread evenly.
How can the Summer Solstice be the First Day of Summer and Midsummer at the same time?
The difference lies in the definitions created by culture, agriculture and astronomy. According to NASA and astronomical institutions, June 21st marks the beginning of Summer in the Northern Hemisphere and the beginning of winter in the Southern Hemisphere.
The official start and end of summer can vary by country - not because summer starts a week or so earlier in one country than another in the same hemisphere, but because the recognition of the start of summer is often influenced by historical or cultural reasons particular to that country. Most countries recognize summer as starting on dates ranging in May and ending sometime in August.
Although the June Solstice marks the beginning of Northern summer, it is often called Midsummer. In traditional Gaelic culture, the Summer Solstice represented the mid-point between the commencement of the Celtic Summer on May 1 and autumn on August 1.
But I thought June, July and August were the Summer months?
They can be if your culture or country recognizes those months as summer. In the U.S., those months have become associated with summer because school vacation (a.k.a Summer Break) has traditionally taken place during those months. But the choice of those months were influenced by the agriculture harvest seasons to allow children to help on the family farm and not due to the official beginning and end of the summer season.
Why is there a lag time between the hottest days of Summer and the Solstice?
Blame the oceans, which heat up and cool down only slowly. By June 21 they are still cool from the winter time, and that delays the peak heat by about a month and a half. Similarly, in December the water still holds warmth from the Summer, and the coldest days are still (on the average - not always) a month and a half ahead.
The 2015 Summer Solstice marks the highest exposure of the northern Atlantic and Pacific Oceans to the Sun's heating radiation. The rise in ocean temperatures then provides the energy necessary to produce stronger hurricanes later in the year, usually around September.