Tuesday, October 1, 2013


I was watching the news last night when I noticed a potential awesome cloud pattern for sunset.  I was lazy and just watched it from my house.  I sort of regret it, since the sunset did maximize.
The beginning color...

Then the color expanded...

The sun is setting farther south now, so to actually see it set into Lake Superior, you have to drive over to Twelve Mile Beach.  The shoreline at that location tilts toward the southwest, so it allows an angle to the sunset.  As I thought about this, I wondered how much this position of sunset changes over the year.

The diagram below shows the path of the Sun on the equinoxes and solstices at a latitude of 40 degrees north.  Due to the tilt of the Earth, the Sun will rise north of true East and set north of true West during summer whereas during winter, the Sun will rise south of true East and set south of true West.

The inclination of the Earth's rotation axis causes the seasons and the position of sunrise and sunset to change every day. The maximum angular distance between two sunrises or two sunsets is the angle between two solstices (June 21, December 21). This angle changes with the latitude of the place. The variation in sunset position is the minimum at the equator and the most at the poles. 

Irrespective of where you are on the globe, the Sun will always rise exactly East and set exactly West on two days: March 21 and September 21 which are the two equinoxes.

For the Upper Peninsula, the length of night and day as well as twilight, sunrise, and sunset times for October 1st are below:
05:56—06:31astronomical twilight
06:31—07:05nautical twilight
07:05—07:34civil twilight

07:37—19:13 — daylight    
19:16—19:46 — civil twilight
19:46—20:20 — nautical twilight
20:20—20:54 — astronomical twilight
20:54—00:00 — night

The chart below shows how the sunrise and sunset times change for Michigan over the course of the year.  The times are average for the state.

January 1st    Sunrise: 8:29am   Sunset: 5:07pm
February 1st  Sunrise: 8:09am   Sunset: 5:47pm
March 1st       Sunrise: 7:24am   Sunset: 6:29pm
April 1st         Sunrise: 7:24am   Sunset: 8:13pm
May 1st          Sunrise: 6:30am   Sunset: 8:53pm

June 1st          Sunrise: 5:55am   Sunset: 9:29pm
July 1st           Sunrise: 5:55am   Sunset: 9:42pm
Aug 1st           Sunrise: 6:25am   Sunset: 9:17pm
Sept 1st           Sunrise: 7:04am   Sunset: 8:25pm
Oct 1st            Sunrise: 7:43am   Sunset: 7:26pm
Nov 1st           Sunrise: 8:26am   Sunset: 6:30pm
Dec 1st            Sunrise: 8:08am   Sunset: 4:59pm

Shortest day is December 21st  -- Sunrise: 8:26am  Sunset: 4:59pm  (daylight=8 hrs 33 min)
Longest day is June 21st           --  Sunrise: 5:51am   Sunset: 9:41pm (daylight=15 hrs 50 min)


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