Today, June 21, is the longest day of the year in the northern Hemisphere and it also marks the official beginning of the summer season.

Depending on the shift of the calendar, the summer solstice occurs between December 21 and December 22 each year in the Southern Hemisphere, and between June 20 and June 21 in the Northern Hemisphere.

As a major celestial event, the solstice happens twice in a year, during summer and winter. The Northern Hemisphere celebrates in June, but the people on the Southern half of the earth have their longest summer day in December.

The summer solstice, which is also called as 'midsummer,' would result in the longest day and the shortest night of the year.

On the day of summer solstice, the Sun reaches its highest position in the sky and this happens when the Earth's North Pole is tilted the most toward the Sun.

The word 'Solstice' comes from the Latin word solstitium, meaning sol (the sun) and stit (standing). The Sun's position at noon actually changes very little in the days surrounding the solstice, hence the concept of the sun standing still, National Weather Service says.

The summer solstice occurs at the moment the earth's tilt toward from the Sun is at a maximum. Therefore, on the day of the summer solstice, the Sun appears at its highest elevation with a noontime position that changes very little for several days before and after the summer solstice.

Due to daylight saving time, the Sun is expected to be at its highest point in Los Angeles at 12:55 p.m., rather than at noon. The exact stopping point of the sun will be at 10:16 a.m. Tuesday.

The summer solstice occurs when the Sun is directly over the Tropic of Cancer, which is located at 23.5° latitude North, and runs through Mexico, the Bahamas, Egypt, Saudi Arabia, India, and southern China.

Worldwide, the event is celebrated in various manners, but most have considered it as a sign of fertility, involving holidays, festivals, gatherings, rituals or other celebrations around that time.

Also, Google welcomed the Summer Solstice by putting a floral doodle called the First Day of Summer by Japanese artist Takashi Murakami on its home page.