On June 20, you can welcome the summer solstice, or the longest day of the year, when the sun shines over the Northern Hemisphere. It's also the time when you are at your happiest self, according to Philip Gehrman, associate director of the Behavioral Sleep Medicine Program at the University of Pennsylvania.
On this day, the sun is directly overhead the Tropic of Cancer, or 23.5° north latitude.
You can be part of the famous Summer Solstice Celebration in Santa Barbara, California. It runs a three-day festival from June 24 to 26----among the world's most eagerly awaited and popular summer solstice events.
The body's circadian rhythms, including its sleep cycle, hormonal fluctuations and body temperature, tend to get affected by light. Most living beings follow a diurnal pattern. The further north you move, the more sunlight you get.
"People tend to feel better in summer months," Gehrman said. "There's a slight elevation in our mood. More positive emotions are reported."
However, circadian rhythms may vary among different people, hence the amount and timing of sunlight may be different too, said Dr. Irina V. Zhdanova, a neuroscience professor at Boston University. Thus, early morning risers get happy when the sunlight shines on them. But they may get irritated by it in the evening.
Moreover, sunlight also tends to make the internal biological clock align itself to the external light-dark cycle. Due to longer days, the circadian rhythm is entrained better, Zhdanova said. In other words, the circadian rhythm is better aligned with natural sunlight and darkness, which can affect people's sleep and moods.
It is not clear, though, whether happy moods are due to entrained circadian rhythms and better sleep, or directly due to sunlight.
She said that even people's mealtimes follow a similar pattern. "Some like three meals a day, others like 10 small meals a day," Zhdanova said. "Sometimes sunlight is good and uplifting during a certain time of the day, while for others, it's neither uplifting or positive and can induce mild irritation."
Less sunlight in winter is also challenging, according to Frank Scheer, director of the Medical Chronobiology Program at Brigham and Women's Hospital.
"The lengthening or shortening of the light period during the day does have a clear effect," Scheer said. "In wintertime, when the days are shorter, we are more likely to wake up when it's still dark outside and before the circadian system stimulates wakefulness and improved mood."
That is why the longest day of the year may be your happiest. After June20, the days may get shorter, after all!
There is one more interesting even waiting for you after Summer Solstice: the Strawberry moon. For the first time since 1967, this eventful solstice coincides with a rare 'strawberry' moon. Soon, the 17 hours of sunlight will lead to a bright moonlit night.
This name was given to the moon by the Algonquin tribes of North America, who thought that the full moon meant the beginning of the strawberry picking season.
