John Vonderlin: A Matter of Degree…What’s Magnetic Declination?

Story  by John Vonderlin

Email John ([email protected])

Hi June,

While looking through some of the historic maps on the Coast Survey website, I came across one showing the magnetic declination in the United States as measured in 1850. As you see, I’ve attached a ScreenShot from that map, showing our local area. It looks like in 1850, the declination, hereabouts, was about 15 degrees 15 minutes. Checking online, I find it is now only 14 degrees 22 minutes at Half Moon Bay.

Without anyone ever complaining, let alone doing anything about it, we’ve lost almost a whole degree in just 150 years. Our declination is in serious decline. Is it sliding down a slippery slope that will leave us declination deficient?  I shudder to think. And if the rising CO2 level line runs afoul of the declining declination line, we could end up lost, hot and thirsty.

For those more interested in facts then my worries, Wikipedia has a very good article on “magnetic declination.” The prize of the article is a map at the very bottom of the page, that cycles through the magnetic declination’s changes around the world, from 1592 to recent times. The expansion and contraction of our magnetic field as portrayed, is quite hypnotic. It’s alive! It’s alive! But, its vital signs are weak and really ssllloooowwwww.


Enjoy. John