After the winter solstice, about December 22nd, the days start getting longer. Not equally on both sides of the day though, but always in favor of sunsets. Sunrise during January is earlier by about 1 minute per day from 21-31 January... (at least in New London, Minnesota).  During the same period, the sunset times increase by 1-2 minutes per day.  Why is it not symmetrical?

Actually, since days are getting longer, and nights are twice as long as days at this time of year, seems to me that sunrise times should be earlier by a larger increment than sunset times are advancing. The ephemeris chart refutes my reasoning.  I asked several astronomers:

     "I don't know. Please expand reason for asking the question." --Bryan X.

Just idle (TIME) curiosity, a discussion around a couple of beers with colleagues after work. My guess was closest, but still not accurate. We finally did come upon the answer. Thank you anyway, Bryan.

Another response: "This screwy timing and why the latest sunrise/earliest sunset does not happen on Dec. 21st has to do with the "Equation of Time" described in my Astronomy Notes web site (in the Naked-Eye Astronomy chapter in the Time and Seasons section)." -- Dr. Nick Strobel <strobel@lightspeed.net>

We received yet another answer from astronomer Steve Willner <willner@cfa183.harvard.edu>.   For those who are interested, here is his response:  

     "This phenomenon is called the 'Equation of Time.' This is just a fancy name for the fact that the Sun's speed along the Earth's equator is not constant. In other words, if you were to measure the Sun's position at exactly noon every day, you would see not only the familiar north-south change that goes with the seasons but also an east-west change in the Sun's position. A graphical representation of both positional changes is the analemma, that funny figure 8 that most globes stick in the middle of the Pacific ocean.

The short explanation of the equation of time is that it has two causes. The slightly larger effect comes from the obliquity of the ecliptic---the Earth's equator is tilted with respect to the orbital plane. Constant speed along the ecliptic --- which is how the "mean sun" moves --- translates to varying speed in right ascension (along the equator). This gives the overall figure 8 shape of the analemma. Almost as large is the fact that the Earth's orbit is not circular, and the Sun's angular speed along the ecliptic is therefore not constant. This gives the inequality between the two lobes of the figure 8."

Analemma -- Sounds like a great pen name for a female astronomer! -- Anna Lemma. (Greg M.)

Some additional discussion, and illustrations, were provided by Dr. Nick Strobel <strobel@lightspeed.net> at http://www.bc.kern.cc.ca.us/programs/sea/Astronomy/ located at Bakersfield College Physical Science Dept.

Dr. Strobel's answer was both the shortest and the longest: "This screwy timing and why the latest sunrise/earliest sunset does not happen on Dec. 21st has to do with the "Equation of Time" described in my Astronomy Notes web site (in the Naked-Eye Astronomy chapter in the Time and Seasons section)." -- This reference is the best college text I have seen on any subject. -Greg Molenaar).
--

All the responses gave me fuel for poetic thought… so here we go:

An Astronomer at the Equation of Time

     An astronomer with a dilemma,
     Sat down with paper -- and penna...
     When she couldn't understand,
     The solstice at hand,
     She graphed out her name: "Ana Lemma".

                              I am almost ashamed to
                              sign my name to this…

                              -- Greg Molenaar (Jan 1999)

...and I have a friend, Andrew, who has plans
to name his future daughter "Andromeda", after all.