Expert: Paul Wagner - 10/7/2009

Question
QUESTION: If east is east and west is west, why does where the sun rises and sets vary by such a huge amount between the peak of summer and the peak of winter?  We are on the west coast in British Columbia, Canada.  Thank you.

ANSWER: Hi Ernie

East is East, and West is West...but those are directions on Earth, and they don't really apply to the heavens.  East and West refer to directions on Earth in relationship to the Poles and the Earth's rotation...while the Sun and Moon follow the ecliptic--which is the plane of the Solar System.  And the Earth is tilted in relationship to the ecliptic.  That's what we have seasons, and why the sun doesn't always rise or set at the same point on the horizon.

And you live in a beautiful place!

Paul Wagner

---------- FOLLOW-UP ----------

QUESTION: HI Paul, thank you for your answer. I think I understand. That being said, would a compass still read due west or east when referring to a sun rise or sunset at the different times of year or would the readings vary?
Thanks.
Yes, we enjoy it here on Vancouver Island very much!
Regards,
Ernie

Answer
Hi Ernie

I am sorry to have to tell you that the magnetic field of the Earth is yet ANOTHER variable in the equation!  The Magnetic Pole isn't exactly where the true North Pole is, so your compass will also not show a true East or West.  In fact, navigators have learned that they need to carry a chart of compass deviations for various locations to effectively get where they are going.

All that to say that The sun's position on  the horizon will vary by about 20% from East or West depending on the time of year.  The only times that the variation will coincide with true East and West are on the Vernal and Autumnal equinoxes---Sept 22 and March 22.  That's when the sun is directly in line with the equator...and thus in line with latitude and longitude!

Paul Wagner