When I was in the 4th grade, Sister Mary Gabriel, would play a game with the globe that resided in the back of the classroom.  The good sister would have a student step up to the front of the class, close his or her eyes, spin the globe, and then randomly stop it with their finger.  And wherever the student’s finger landed would be our “homework” for the week. We only had to write a single paragraph about the location, but it was one of the most enjoyable (and informative) geography lessons I ever had.  Obviously since globes are all canted with a Northern Hemisphere bias, the South Pacific and Australia got the short shrift, but one day when it was my turn to spin, my finger landed square on Greenwich England, home of the prime meridian.

Unless you’re a progressive, you probably studied in school and know what the prime meridian is, nevertheless, I thought it would make for an interesting blog post.  So, let’s start with the definition of an earth meridian – An earth meridian is an imaginary line that runs from north to south on a map.  There are 360 meridians around the glove (one for each degree, duh!) and the prime meridian is the starting point for measuring all the others.  At a longitude of 0 degrees, it denotes the separation between the Eastern and Western Hemispheres with 180 meridians to the east and 180 meridians to the west.

Interesting too, it was the implementation of the prime meridian in Greenwich, England, in 1884 that unified the globe in its measurements, resulting in all maps being drawn according to the prime meridian’s longitudinal location.  But because the Earth is not a perfect sphere and the fact that gravitational forces vary with terrain (betcha didn’t know that!), the surface of the mercury used for measurement at Greenwich is not precisely horizontal relative to the prime meridian.   Consequently, the meridian line as displayed at the Royal Observatory where the meridian is located, is slightly skewed and should be 102 meters to the east.

But before going further, let’s remember the position of the prime meridian is arbitrary and could theoretically be located anywhere.  And the reason Greenwich was chosen is because that’s where conferees at the International Meridian Conference of 1884 decided to place it.

We know that all important scientific measurements in the 21st century are made using Global Positioning Systems and not the misplaced meridian, rendering the impact of the error minimal.  And arguably, the issue should be confined to the Royal Observatory itself and how it plans to address the issue with the thousands of tourists who visit each year.  One can argue the need for a new marker at the “true” prime meridian, but since current meridian is literally “set in stone,” i.e., it’s a painted concrete & metal ‘ribbon’ imbedded into the cement at the Royal Observatory in Greenwich, England that’s probably unlikely.

So, are there other important meridians?  Glad you asked because shortly after the world was divided into time zones, the International Date Line became one of the planet’s most important meridians.  It too was established in 1884 and located halfway around the globe from the prime meridian.  The IDL as those of us who study such things refer to it, follows the 180-degree meridian with a few zigzags around political borders such as eastern Russia and Alaska’s Aleutian Islands as it passes through the mid-Pacific Ocean.

Interesting too, the International Date Line has no legal status, which is likely one reason the IDL has a disjointed course, which when crossed, will either add or subtract 24 hours from an individual’s day.

Meanwhile, the Tropic of Cancer is also a line, but it’s a latitudinal one, also known as a parallel that runs from east to west around the globe.  In addition to the equator, it is one of the five major parallels on Earth (the other three being the tropic of Capricorn, the Arctic Circle, and the Antarctic Circle). Located 23.5 degrees north of the equator.

The Tropic of Cancer plays an important role in the sun’s geographical relationship to the Earth because it denotes the northernmost point on Earth where the sun is directly overhead at high noon.  This happens annually on the summer solstice (for the Northern Hemisphere) in June.  Then, after reaching this point, the sun’s rays travel south until they reach the same angle at the Tropic of Capricorn in the Southern Hemisphere, which happens in December on the winter solstice

Allow me to end this blog by commenting that I’ll bet the next time you come across a globe somewhere, you’ll take a minute or two to identify a few of these lines.

Quote of the day: “There are shortcuts to happiness and dancing in one of them.”—Vicki Baum