Why days are longer and nights are shorter in Southern Hemisphere during the month of December

MEMPHIS, Tenn. (WMC) -The winter solstice marks the official start of winter in the northern Hemisphere which began Monday Dec. 21 at 4:02 a.m. Central time. It marks the shortest day and the longest night.

This is due to earth rotating around the sun and the tilting of the earth on it’s axis. It takes the earth 365 days, a year to rotate around the sun. Meanwhile, it is also spinning on it’s axis which takes 24 hours. Earth is tiled 23.5 degrees, this means as it orbits the sun, it changes the way in which it faces it. When it is tilted away it is winter.

During the winter, the sun’s rays hit the Earth at a shallow angle. The sun’s rays are more spread out, which decreases the amount of energy that hits any given spot. The long nights and short days prevent the Earth from warming up. This is why we have winter.

On the other hand, in the summer, the sun’s rays hit the Earth at a steep angle. The light is more concentrated and does not spread out as much, thus increasing the amount of energy hitting any given spot. The long daylight hours allow the Earth plenty of time to reach warm temperatures.

The solstice can occur anywhere between Dec. 20-23 and this year it is on the 21st. The winter solstice marks the minute the sun is directly over the Tropic of Capricorn. Earth is actually closest to the sun.

The word solstice comes from Latin sol “sun” and sistere “to stand still.” On the 21st of December, the sun’s path reaches its southernmost position. While it starts to return north, it gives the appearance of standing still.

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

In December, the North Pole is tilted away from the Sun.

© timeanddate.com

The December solstice is the moment the Sun is directly above the Tropic of Capricorn in the Southern Hemisphere. This is the southernmost latitude it reaches during the year. After the solstice, it begins moving north again.

10 facts about the December solstice

Solstice Local Time & Date

Shortest Day in the North

Since the Northern Hemisphere is tilted away from the Sun in December, it receives less sunlight during the course of a day. At the solstice, the North Pole's tilt away from the Sun is greatest, so this event marks the shortest 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 shortest day is just a little shorter than 12 hours; in the temperate zone, it is significantly shorter; and places within the Arctic Circle experience polar night, when the Sun does not rise at all.

Longest Day in the South

Conversely, the day of the December solstice is the longest 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 Midnight Sun, when the Sun does not set at night.

Sun times at the South Pole in December

What Does “Solstice” Mean?

During the course of 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 northernmost point at the June solstice, it starts moving southward until it crosses the equator on the day of the September equinox. At the December solstice, which marks the southernmost point of its journey, it stops again to start its journey back toward the north.

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 December solstice, the position of sunrise and sunset creeps southward. On the day of the solstice, it reaches its southernmost point. After that, the daily path of the Sun across the sky begins to creep northward 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 December solstice marks the start of winter in the Northern Hemisphere and the start of summer in the Southern Hemisphere, according to one definition.

Equinox and solstice dates—years 1-2149

Sunrise and Sunset Times Lag Behind

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

The December Solstice in the Calendar

The December solstice can be on December 20, 21, 22, or 23.

December 21 or 22 solstices happen more often than December 20 and 23 solstices. The last December 23 solstice was in 1903 and the next one is in 2303. A December 20 solstice is also rare, with the next one in the year 2080.

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, December, Solstice, Earth

Updated June 25, 2019

By Amy Dusto

Northern Hemisphere dwellers, or most of the Earth's population, have probably all noticed longer days and shorter nights in the summer and the opposite in winter. This phenomenon occurs because the Earth's axis is not straight up and down at a 90 degree angle, but it is instead tilted a bit.

Therefore, as the planet orbits the sun every 365 days, sometimes the Northern hemisphere is closer to the sun (summer) while sometimes it is farther away (winter).

To explain why days are longer in summer and shorter in winter, first consider the two ways the Earth is rotating all the time.

It spins around its axis, or the imaginary line running through the North and South poles, every 24 hours so that part of the planet is always facing the sun (experiencing daytime) while the opposite side of the planet is not (experiencing nighttime). Meanwhile, the Earth is also orbiting the sun, completing its circle every 365 days.

If the Earth's axis was straight up and down at 90 degrees, the length of time spent facing the sun would always equal the length of time facing away. But it isn't.

Instead, the Earth is tilted slightly at 23.5 degrees to be exact. Additionally, this tilt is always pointed in the same direction in space, toward Polaris (the North Star), even as the planet travels in a circle around the sun. This means that throughout its yearly orbit, sometimes the Northern hemisphere is closer to the sun (summer) while sometimes it is farther away (winter).

Depending where you are on the planet, the difference in the length of day from season to season can be larger or smaller.

Latitude is a measurement that locates a point on a planet in relation to its distance from the equator. Higher latitudes are closer to the poles, while 0 degrees in latitude is the equator itself.

Because the Earth is a sphere, the higher latitudes near the poles are already curving away from the Sun and therefore receiving less sunlight every 24 hours. This is why the poles stay colder than the rest of the planet.

Therefore, with an additional 23.5 degree tilt away from the Sun, a pole receives even less light, and it will only experience daytime in the short window when its lowest part is in line with the Sun's rays. In fact, in the middle of winter, the sun never fully rises above the horizon, and it is essentially 24 hours of night; in the summer, the reverse is true.

The combination of the Earth's tilt and its rotation about the Sun mean that on one day a year, the North Pole ends up tilting as far as possible toward the Sun while the South Pole is tilted as far away as possible. This results in the longest day of the year, also known as the summer solstice, for all locations in the Northern Hemisphere, and the shortest day in the Southern Hemisphere, called the winter solstice.

Halfway between the solstices are the equinoxes. This marks the point in Earth's orbit where the planet's tilt switches its orientation either toward or away from the Sun. At one hemisphere's spring equinox, the tilt changes from away to toward the Sun, lengthening the subsequent days until the fall equinox, when the opposite occurs.

The solstices and equinoxes have variable dates due to small accounting differences in the Earth's orbit (a year is slightly more than 365 days) and calendar systems.

However, the first day of a season as usually defined on a calendar falls near the same dates as these astronomical events. In the Northern Hemisphere, the winter solstice occurs around December 22; summer solstice, June 22; spring equinox, March 21; and fall equinox, September 23.