What is the longest day of the year in my area?

The summer solstice occurs once a year in December when the Sun's track across the Australian sky reaches its highest point. It is the day that has the most daylight hours of any in the year. The summer solstice usually occurs on 22 December, but can occur between 21 and 23 December. The winter solstice is the day of the year that has the least daylight hours of any in the year and usually occurs on 22 June but can occur between 21 and 23 June.

Sunrise, sunset and daylight hours

An interesting idiosyncrasy relating to the summer solstice is that it does not feature the day with the earliest sunrise and latest sunset as is commonly expected. Similarly, on the winter solstice, the sunrise is not the latest and the sunset is not the earliest. However, this day does have the least amount of daylight hours.

Because the path of the Earth around the Sun is an ellipse, not a circle, and because the Earth is off-centre on its axis, these combined phenomena can create up to several minutes difference between solar and mean time. Around the date of summer solstice, these effects make the Sun appear to move slightly slower than expected when measured by a watch or clock. As a result, the earliest sunrise occurs before the date of the summer solstice, and the latest sunset happens after the summer solstice. For the same reasons, around the winter solstice, the time of sunrise continues to get later in the days after the solstice.

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.

Position of Earth in relation to the Sun during the June solstice.

© timeanddate.com

Sun Reaches Most Northerly Point

The June solstice is the moment the Sun is directly above the Tropic of Cancer in the Northern Hemisphere. This is the northernmost latitude it reaches during the year. After the solstice, it begins moving south again.

11 facts about the June solstice

Solstice Local Time & Date

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.

Sun times at the South Pole in June

Why Is It Called a “Solstice?”

During a year, the subsolar point—the spot on the Earth's surface directly beneath the Sun—slowly moves along a north-south axis. Having reached its southernmost point at the December solstice, it stops and starts moving northward until it crosses the equator on the day of the March equinox. At the June solstice, which marks the northernmost point of its journey, it stops again to start its journey back toward the south.

This is how the solstices got their name: 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.

Earth: The living planet

The Sun: Our home star

Why Does the Sun Move North and South?

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.

How do seasons work?

Earth is tilted as it orbits the Sun, which is why equinoxes and solstices happen.

©timeanddate.com

The Solstices and the Seasons

The June solstice marks the start of summer in the Northern Hemisphere and the start of winter in the Southern Hemisphere, according to one definition.

Equinox and solstice dates—years 1-2149

Sunrise and Sunset Times Lag Behind

The longest day of the year is commonly associated with the earliest sunrise and latest sunset of the year. However, in most locations, the earliest sunrise happens a few days before the solstice, while the latest sunset occurs some days after it. Find out why

The June Solstice in the Calendar

Even though most people consider June 21 as the date of the June solstice, it can happen anytime between June 20 and June 22, depending on the time zone. June 22 solstices are rare—the last June 22 solstice took place in 1975, and there won't be another one until 2203.

Note: All dates refer to Coordinated Universal Time (UTC). Local dates may vary depending on the time zone.

Why Does the Date Vary?

The date of the equinoxes and solstices varies because a year in our calendar does not exactly match the length of the tropical year—the time it takes the Earth to complete an orbit around the Sun.

Today's Gregorian calendar has 365 days in a common year and 366 days in a leap year. However, our planet takes about 365.242199 days to orbit the Sun. This means that the timing of the equinoxes and solstices slowly drifts apart from the Gregorian calendar, and the solstice happens about 6 hours later each year. Eventually, the accumulated lag becomes so large that it falls on the following date.

To realign the calendar with the tropical year, a leap day is introduced (nearly) every four years. When this happens, the equinox and solstice dates shift back to the earlier date again.

Other factors influencing the timing of the equinoxes and solstices include variations in the length of a tropical year and in the orbital and daily rotational motion of the Earth, such as the “wobble” in the Earth's axis (precession).

Topics: Astronomy, Sun, Seasons, Calendar, Solstice, Earth

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