Each solar day is approximately 24 hours and 30 seconds long around the December solstice. That is, it takes slightly longer than 24 hours for the sun to appear in the same location in the sky from one day to the next. The length of a solar day gets shorter as you get farther from the equator, but even at the poles it will take the earth about 25 days to completely circle the sun.
There are also two other points in time when the length of a day is exactly 12 hours: at the spring and fall equinoxes. At these times, the sun is directly over the equator, so days and nights are of equal length.
During the months surrounding the December solstice, the length of daytime decreases at a rate of 1 minute per hour north of the equator and 2 minutes per hour south of the equator. By the summer solstice in June, the length of daytime has decreased by about 14 minutes south of the equator and 21 minutes north of the equator.
These are very rough estimates, but they should be good enough for most applications. In practice, actual daily sunlight changes many times during the year due to clouds, air pressure, elevation, etc.
The amount of daylight at any given time depends on how far north or south you are and what part of the year it is.
"As a result, we utilize 24 hours as the yearly average for all timekeeping reasons." As a result, while the solar days in December are on average 24 hours and 30 seconds, and our clocks and watches continue to assume that each day is exactly 24 hours, the day shifts roughly 30 seconds later each day. At the winter solstice, the sun is at its farthest point from the Earth in the direction of its orbit, which is why we call it the "winter" solstice; however, since the Earth is not perpendicular to the Sun's orbit, at this point it is also at its closest approach to the Sun and receives less energy than at any other time of the year.
During the winter months, daytime temperatures across the globe tend to be lower than normal, which is why scientists believe that nocturnal sunlight is responsible for much of the ice that forms over land during the winter months. The ice that does form due to daylight hours does so because it has a higher temperature than the surrounding air, so when rain falls it can't melt away the ice that has formed during the night. The amount of sunlight that reaches the ground during the winter months is called the "photoperiod". Photoperiodism is when an organism's behavior or physiology changes depending on how much sunlight it receives.
When will the days lengthen? Every day following December 21st, the days lengthen by an average of 2 minutes and 7 seconds. An extra hour of daylight will not arrive until approximately January 18th, and an hour or two of sunshine should enhance the days every 28 days (four weeks) after that.
The amount of sunlight we receive varies from season to season, and even within a given season if you live near a large body of water. But on average, daily light levels decline during the month of December and increase again in March.
Light bulbs emit different wavelengths of light at different times during their lifespan, so replacing them is an easy way to adjust how much of these different wavelengths is coming into your home. Old lamps tend to produce more blue light, while modern lamps tend to do so more often than not. It's best to replace all of your lamps together since they share the same housing.
During winter, the quality of light drops dramatically because only certain parts of the spectrum are able to penetrate the clouds and rain that tend to block out most of the sun. However, this also means that more of the light is actually reaching ground level, which is why winter doesn't feel as dark during those months.
A solstice occurs when the sun's zenith is furthest from the equator. The December Solstice, also known as the Winter Solstice, takes place on or around December 21st, when the sun reaches its greatest southerly declination of 23.5 degrees. In other words, when the North Pole is inclined 23.5 degrees away from the Sun, which is why the term "southern hemisphere" was coined for that part of the Earth's surface during the winter months.
The summer solstice occurs when the sun's zenith is closest to the equator. The June Solstice, also known as the Summer Solstice, takes place on or around June 20th, when the sun reaches its greatest northness of 53.3 degrees. Like the winter solstice, the summer solstice marks the beginning of autumn and winter in the Northern Hemisphere. It is followed by a period of decreasing daylight length called "winter darkness." The opposite phenomenon occurs in the Southern Hemisphere where spring dawn arrives first near the South Pole and then spreads southward across the remainder of the continent by about 10 days per decade.
Since the axis of the Earth is not perpendicular to its orbit, but instead leans slightly toward the Moon, each year the distance between the North and South Poles changes. On average, the polar ice caps melt away, making room for more dark earth beneath the snow.