Daylight Time Expansion

Question

I live in northern hemisphere around 44th latitude. Starting from Winter Solstice, December 21, 2018 the duration of daylight is naturally increasing. What I observe, however, is that the duration increase is happening more in the evening rather than in the morning. In other words as days pass, the sunset seems to move forward much faster to a later hour than the first morning light moving backward to an earlier hour.

Is what I am observing a true phenomenon or is it merely a wrong observation? If so why is this happening in an uneven fashion?

EDIT

I found the sunrise/sunset times for my area. It in fact confirms the situation. In the first half of January sunrise moved back only 3 minutes while sunset moved forward 15 minutes with respect to civil time.

Answer 1

This phenomenon is the equation of time, the annually varying difference between apparent solar time (what a sundial indicates) and mean solar time (related to civil time). It has two components:

• The eccentricity of the Earth's orbit around the Sun causes a cycle with 7.5-minute amplitude and 12-month period, with zeroes at perihelion (Earth moving fastest and closest to the Sun) and aphelion (Earth moving slowest and farthest from the Sun).

• The oblique angle between the Earth's equator (rotation plane) and ecliptic (orbital plane) causes a cycle with 10-minute amplitude and 6-month period, with zeroes at equinoxes (Sun crossing Earth's equator) and solstices (Sun farthest north or south of the equator). This answer explains how that works.

These combine so that apparent solar time is 17 minutes ahead of mean solar time in early November and 14 minutes behind in mid February. Between those times of year, the apparent Sun falls several seconds behind the mean Sun each day, affecting both sunset and sunrise times as you observed.

For further explanation, see the US Naval Observatory or Wikipedia.

Answer 2

Below is a graph of the sun rise and set times. As you can see, the changes in the morning and evening are not exactly symmetric. The difference is more pronounced when the Earth is closer to the sun and moving faster (January), and less so in July when the Earth is furthest from the Sun.

In the Northern hemisphere, the earliest sunset is around Dec 5, and the latest sunrise around Jan 5. But, in June, the latest sunset, and earliest sunrise are only separated by about a week.

This is due to the combination of two effects. 1. Is the apparent change in RA/Dec of the Sun throughout the day, which changes faster based on the Earth's orbital speed. And 2. The time difference between sun rise and set (e.g. since summer nights are short, the sun will move more during the daytime than the nighttime). It it quite a small effect, but very obvious on a graph.

The graph below was generated for 44°N using this Astronomical Rise and Set Calendar.

Here is the same graph, but centered on (northern) winter, to make the offset more apparent.