Winter solstice, sunrise and sunset time

It is happening because of the acceleration of the Earth orbital speed around the Sun (Earth is near the perihelion). Between December 13 and December 31 the Earth is speeding up and also it is normally rotating around its axis. These 2 movements (constant rotation and increasing orbital speed) add up to create the observed apparent movement of the Sun on the Earth sky. The Sun rises later and also sets later every day.

It is a bit tricky to visualize, so try it with a globe.

There are two causes of this and other effects which are basically that noon as measured by the Sun, i.e. when it is due south, is usually not the same as noon by local clock time. The two phenomena are: the speeding and slowing of the Earth in its elliptical orbit round the sun, and the inclination of the Earth's axis to the plane of the ecliptic. If we kept clock noon the same as Solar noon, then days would vary rather awkwardly in length through the year. Here at latitude 52 degrees North, noon today, 4th December, is about 11-53, and changes quite rapidly to 12-07 p.m. in a month's time. It "drags" dawn with it, so mornings stay dark well into January, while sunset begins to advance, giving us short mornings and longer afternoons.

At any particular location, the situation is made slightly more complicated by the use of time zones.

It's the reason why we have "Greenwich mean time, which is calculated as though the sun moved at a constant speed in a circular path round the Earth, to give us days of equal length, exactly 24 hours between successive noons. (almost exact-- someone will cavil)

This effect is rather curiously known as "the equation of time" and a good account is given at: http://en.wikipedia.org/wiki/Equation_of_time. There is a detailed description of time and its measurement in the book "Greenwich Time and the Longitude" by Derek Howse, published by Greenwich Observatory.

Think about this :

People that live on the equator have 12 hours of day and twelve hours of night all year ! If the earth's axis was perpendicular to the plane of its orbit (ecliptic) everyone would have twelve hour days and nights all year. But that ain't the model. The axis is ~ 23.5 degrees to the perpendicular. The plane containing the Earth axis and the line from earth center to sun center is perpendicular to the ecliptic twice a year ,i.e. the solstices . These do not coincide with earth's apogee and perigee about the sun .

Currently, the Earth reaches perihelion in early January, approximately 14 days after the December Solstice. At perihelion, the Earth's center is about 0.98329 astronomical units (AU) or 147,098,070 kilometers (about 91,402,500 miles) from the Sun's center.

The Earth reaches aphelion currently in early July, approximately 14 days after the June Solstice. The aphelion distance between the Earth's and Sun's centers is currently about 1.01671 AU or 152,097,700 kilometers (94,509,100 mi).

a good read may be found at

https://en.wikipedia.org/wiki/Apsis

MAY THE FORCE BE WITH YOU !