Autumnal Equinox: The Shadows Dominate

Today is the Autumnal Equinox.  The Sun will be directly (center of disc) over the equator at 9:29 PM CDT.  It is often referred to as the First Day of Autumn, although, I have personally never understood the justification for that for a number of reasons (although there is an obvious seasonal lag).  If you live in the middle latitudes the Autumnal Equinox always marks the beginning of what I reference as the “shadow season”.  With the Sun directly over the equator today and with North Dakota situated between 46° and 49° north latitude, even at solar noon, the shadows are now longer than the object’s height.

The Twin Cities are located along or near 45° north latitude.  Meaning on the two equinoxes the Sun’s angle at solar noon would be at 45° above the horizon.  At that latitude the object and the shadow would be of the same length, but in North Dakota, such a sight will not be visible again until the end of March.  With the Sun’s direct rays moving southward until the Winter Solstice, the shadows will only lengthen during the next few months.

Today the Sun will reach only from 44° to 41° (from south to north) above the horizon across North Dakota at solar noon.   On the winter solstice the sun will only be from 20.5° to 17.5° (from south to north) above the horizon at solar noon.  With such a low sun angle and the usual snow cover, plus, far from the influences of a large body of unfrozen water, it is no surprise this area is so cold during the “low sun” season.

Below are solar graphs for Fargo, Bismarck and Crosby, North Dakota to give you Sun angles and sunrise and set positions over the course of the year.

Fargo Solar Chart
Fargo Solar Chart from December to June

 

Fargo Solar Chart from June to December
Fargo Solar Chart from June to December

 

Bismarck/Mandan Solar Chart
Bismarck/Mandan Solar Chart December to June
Bismarck / Mandan Solar Chart  June to December
Bismarck / Mandan Solar Chart June to December
Crosby Solar Chart
Crosby Solar Chart December to June
Crosby Solar Chart June to December
Crosby Solar Chart June to December

 

Daryl Ritchison