Monday, November 19, 2012

What Direction Does the Sun Rise and Set?

As children, we are all taught that the Sun rising in the East and sets in the West.  Although this is partly true, it's also a misconception.  It's true the the Sun rises SOMEWHERE in the East and sets SOMEWHERE in the West.  Where exactly in the east the Sun rises and in the west the Sun sets depends on the day of the year.  Assuming you are not living above the Arctic Circle or below the Antarctic Circle, there are only two days a year that the Sun rises directly East and sets directly West.  These are the first day of Spring, around March 20/21 and the first day of Fall, around September 20/21.  On every other day of the year, the Sun does NOT rise directly East, and it does NOT set directly West.

Why not?  This is due to Earth's 23.5 degree axis tilt and Earth's revolution about the Sun.  As Earth revolves around the Sun, the position of the Sun at rise and set time changes.  As the days proceed from the first day of Spring to the first day of Summer, the Sun's rise position slowly shifts to the North East.  Note the diagram (for someone standing in Earth's northern hemisphere) below showing Sun rise and set positions at different times of the year.



After June 20/21 (first day of summer) until December 20/21 (first day of winter) the Sun's rise position changes from northeast to east to southeast.  Then the position reverses back from southeast to north east as we go from winter to summer.  The same is true in the West when the Sun sets.

This is a hard misconception to remove from the brains of high school students.  Everyone thinks that the Sun rises in the East, but the key is that it rises SOMEWHERE in the East.  Take a look at the rise position of the Sun at different times of the year.  You've all done this before without realizing it.  Every Spring and Fall we complain about the Sun being in our eyes when we drive to work and/or home from work.  How many of you have been driving to work in the morning near the first day of Spring or Fall and come to a stop at a stoplight but can't see when the light changes because the Sun is right there, blasting into your eyes?  Happens to me every equinox.  But a couple of week's later it's not a problem because the rise position of the Sun has changed.  Show this to your kids sometime, but be careful and explain to them that they shouldn't stare directly at the Sun.


1 comment:

  1. Due to light diffraction caused by the atmosphere the sun will appear to set directly in the west a few days before the actual spring equinox. As an example, today, March 17, 2016, in Chicago. the sun went down in the "middle" of our east west streets, yet true equinox occurs on the 20th. So, for me, today marks the end of winter.

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