Summer Solstice or June Solstice

 

Equinoxes and solstices are a result of two things: Earth’s tilt and its orbit around the Sun.

Solstice, the term comes from the Latin words sol and sistere, meaning “Sun” and “to stand still”.

Initially, the naming arose from observations of how the Sun’s apparent path across the sky changes slightly from one day to the next, which is caused by the same process as the subsolar point's movement described above.

In the months leading up to the June solstice, the position of sunrise and sunset creeps northward. On the day of the solstice, it reaches its northernmost point. After that, the daily path of the Sun across the sky begins to creep southward again.

The summer solstice or estival solstice occurs when one of Earth's poles has its maximum tilt toward the Sun. It happens twice yearly, once in each hemisphere (Northern and Southern). 

Compared to its orbital plane, Earth’s axis of rotation is tilted by about 23.4 degrees. This is referred to as Earth’s axial tilt or obliquity.

However, as Earth travels along its orbit, its tilt changes with respect to the Sun.

The subsolar point moves north and south during the year because the Earth’s axis is tilted at an angle of about 23.4° in relation to the ecliptic, an imaginary plane created by Earth’s path around the Sun. In June, the Northern Hemisphere is tilted toward the Sun, and the subsolar point is north of the equator. As the Earth travels toward the opposite side of its orbit, which it reaches in December, the Southern Hemisphere gradually receives more sunlight, and the subsolar point travels south.

For six months of the year, the North Pole is tilted toward the Sun, and the Sun lies somewhere above the Northern Hemisphere. For the other six months, the South Pole is tilted toward the Sun, and the Sun lies somewhere overhead the Southern Hemisphere.

There are two solstices every year: one in June and one in December. The June solstice marks the longest day north of the equator and the shortest day in the south.

The Solstices

The farthest points from the equator where the Sun can appear directly overhead are referred to as the tropics.

The tropics are lines of latitude that circle the Earth above and below the equator, at about 23.4 degrees north and south. This angle is set by Earth’s axial tilt.

There are two moments each year when one of Earth’s poles is tilted the most toward the Sun, and the Sun lies directly above one of the tropics. These moments are the solstices.

The June solstice takes place sometime between June 20 and 22, when the Sun is directly above the Tropic of Cancer in the Northern Hemisphere. As a rough guide, the Tropic of Cancer passes through Mexico, northern Africa, the Middle East, India, and China.

The December solstice happens sometime between December 20 and 23, when the Sun is directly over the Tropic of Capricorn in the Southern Hemisphere. In brief, the Tropic of Capricorn runs through South America, southern Africa, and Australia.

In the Northern Hemisphere, the June solstice and December solstice can be referred to as the summer solstice and winter solstice. In the Southern Hemisphere, June is winter and December is summer.

On the date of the summer solstice, all locations in that hemisphere experience their longest days and shortest nights. The winter solstice produces the shortest days and longest nights.

Longest Day in the North

Since the Northern Hemisphere is tilted toward the Sun in June, it receives more sunlight during the course of a day. The North Pole's tilt toward the Sun is greatest at the solstice, so this event marks the longest day of the year north of the equator.

This effect is greatest in locations that are farther away from the equator. In tropical areas, the longest day is just a little longer than 12 hours; in the temperate zone, it is significantly longer; and places within the Arctic Circle experience Midnight Sun or polar day, when the Sun does not set at night.

Shortest Day in the South

Conversely, the day of the June solstice is the shortest day of the year in the Southern Hemisphere. Here, too, the effect is greater the farther a location is away from the equator.

Places within the Antarctic Circle experience polar night, when the Sun does not rise at all.

Equinoxes and Solstices on Other Planets

Every planet in the solar system, apart from Mercury, is tilted on its axis of rotation. This means each planet has its own equinoxes and solstices.

Venus and Jupiter have small axial tilts of 2.6* and 3.1 degrees, respectively. Venus orbits the Sun more quickly than Earth—in Earth time, an equinox or solstice happens on Venus every couple of months or so. Jupiter orbits more slowly; an equinox or solstice occurs there about every three Earth years.

Mars, Saturn, and Neptune have tilts similar to Earth’s: the values are 25.2, 26.8, and 28.3 degrees, respectively. At the equinoxes on Saturn, the planet’s famous rings appear edge-on as seen from Earth.

Uranus has an axial tilt of 97.8 degrees. This is close to a right angle, meaning the planet appears to lie on its side. Around the solstices on Uranus, the Sun is almost directly overhead one of the planet’s poles.

Venus spins in the opposite direction to most planets, its tilt can be given as 177.4 degrees. In other words, Venus can be thought of like it is spinning upside down.