Non Equi Equinox ?

The Vernal Equinox, more commonly referred to as the Spring Equinox,
occurs March 20 this year. On this day, the noontime sun is shining
directly on the equator of the earth, while at the North Pole the sun peaks
above the horizon for the first time in 6 months1
. As the name “equinox”
implies, every place on the planet should observe 12 hours of daylight and
12 hours of night, but as the table below shows, this isn’t exactly the case
(Table 1).
Location Sunrise Sunset Difference
Fort Dodge 7:20 AM 7:29 PM +9 minutes
Mason City 7:17 AM 7:25 PM +8 minutes
Waterloo 7:13 AM 7:21 PM +8 minutes
Des Moines 7:18 AM 7:26 PM +8 minutes
Creston 7:21 AM 7:29 PM +8 minutes
Ottumwa 7:14 AM 7:22 PM +8 minutes
Table 1: The table able above shows the sunrise and sunset times (CDT) for various sites
across Iowa2. The yellow column on the end shows the difference between sunset and sunrise,
with positive values indicating more daylight.
Why isn’t here exactly a 12 hour difference between sunset and sunrise?
There are two reasons that explain the discrepancy. The first is a result of
how “sunrise” and “sunset” are defined. According to the American
Meteorological Society, sunrise occurs with the first appearance of the sun
on the eastern horizon, and sunset occurs with the last disappearance
below the western horizon. However, the equinox uses the center point of
the sun. Therefore, the 3 or 4 minutes difference between the first sliver of
sun and the center point at sunrise, and the last sliver of sun and the center
point at sunset is one part of the reason why there is a few minutes more of
sunlight during the Spring Equinox (Figure 1).
The second reason is because as sunlight enters the atmosphere, it
refracts, or bends slightly. Therefore even though the sun is actually below
a person’s line of site, the rays bend and the observer can actually see the
sun on the horizon before it rises, or after it sets

 

As an aside, I only learnt this year that we actually see the Sunrise about two minutes before the Sun actually shows above the horizon and the same applies to the Sunset, we still see it for around 2 minutes after it has disappeared below the horizon. Why?, all due to the bending of light in the atmosphere.

 

I never change my Clocks I either change the batteries or wind them up