Sunrise and Sunset

   

     Unless a city observer has a well-positioned window, the rising and setting of the Sun is commonly a problem.  

     Nevertheless, the rising and setting of the Sun are fascinating phenomena if for no other reason than that they change in such a dramatic way in the course of a year!

     For example, in August, Maine in 2001, the sun rises on the first day of winter (on or about December 21) the Sun rises at 7:11 AM and sets at 4:02 PM.  Yet, on the first day of summer, it rises at 4:55 a.m. DST (3:55 Eastern Standard Time!) and sets at 8:26 p.m. DST.

     Looking at this graphically:

For Augusta, Maine

(All times Eastern Standard Time)

December 21                 June 21

                                     Rise:      7:11 a.m.                   3:55 a.m.

                        Set:        4:02 p.m.                  7:26 p.m.

     For Augusta, Maine the Sun is in the sky for less than eight hours on the first day of winter, but in the summer is in the sky over 15 hours.  No wonder summer is a warm season:  Summer daylight is nearly twice as long, at least in Maine.

     Especially for observers in the city, this is a stunning difference, where high buildings cast long shadows when the Sun is low, as it is for a preponderant fraction of the day in late fall and winter.  And the change in the apparent altitude of the noon Sun is just as dramatic as the change in daylight.  They are intimately related.

     Augusta is a good example of the changing length of daylight and night with the seasons. However, cities to to the south have somewhat less dramatic differences, though differences nonetheless:

For Jacksonville, Florida

(All times Eastern Standard Time)

December 21                 June 21

                                     Rise:       7:19 a.m.                   5:25 a.m.

                         Set:        5:30 p.m.                   7:31 p.m.

     Jackonville has a less dramatic change in the length of daylight and dark with the seasons.  In winter the daylight period is about 10 hours, while in winter it is about 14 hours.

     Most city observers in the United States will observe changes less dramatic than these.  It is an easy matter to determine the times of sunrise and sunset for your city, or for that matter, to determine the times of the rising and setting of the Moon as well.

     This change in sunrise and sunset times is related to the places on the horizon where the Sun rises and sets.  On the first day of spring and fall, it rises due east and sets due west.  However, on the first day of winter the Sun rises and sets well to the south, spending less time in the sky because the its path (its arc) is shorter.  On the first day of summer it rises and sets well to the north of east or west, the longer arc accounting for the increased period of daylight.

     All of us have probably responded to this change and not realized it:  We may not have noticed that only on certain days of the year do we need to lower the sunvisor as a certain stretch of highway heads us toward the Sun.