🌐 HOMESCHOOL GEOGRAPHY: The Prime Meridian

To specify your location on the surface of the earth, you need to give your latitude and your longitude. Determining your latitude (north or south of the equator) is fairly straightforward. The north pole (90ºN latitude), the south pole (90ºS latitude), and the equator itself (0º latitude) are not artificial constructs: they are fixed by our planet’s daily rotation. And in the northern hemisphere you can always make a rough and ready estimate of your latitude by measuring the height of Polaris (the North Star or Pole Star) above the level horizon — that angle corresponds to your latitude in degrees north (of the equator).

So latitude is given as degrees north or south of the equator, but longitude is given as degrees east or west of … what? There is no natural zero-line for longitude as there is for latitude (the equator).

Since there’s no natural zero-degrees-longitude line, we have to just pick one to use, and that’s exactly what happened on this day, October 13th, in 1884 at the International Meridian Conference in Washington, D.C. The line chosen as the earth’s Prime Meridian — the line of 0º longitude — was the line running north–south through the Royal Observatory at Greenwich, England, one of the world’s principal research centers for timekeeping and navigation. And from that day forward, the longitude of every spot on earth has been measured in degrees east or west of the Greenwich Prime Meridian, just as the latitude of every spot on earth is measured in degrees north or south of the equator.

You can visit the Royal Observatory some day on your homeschool travels if you like, and as thousands of people do every year, you and your students can stand astride the Prime Meridian — an actual line constructed on the Observatory’s grounds — with one foot in the world’s eastern hemisphere and one foot in the west:

• ➢ The Prime Meridian (rmg.co.uk)

So wherever you may be this week, take out your homeschool atlas and use the maps to determine your longitude. The longitude value you find will be in degrees east or west of the Prime Meridian, established on this day in 1884 as the north-south line that passes through the Royal Observatory at Greenwich.

What grand geographical discoveries have you and your students made in your homeschool this Cygnus Term? 😊

❡ Meridians and parallels: To teach students about longitude and latitude you really need to use a globe rather than a map. (If you don’t have one, take a look at the inexpensive inflatable globes we recommend for homeschool use.) The lines of longitude are called meridians and the lines of latitude are called parallels. The meridians all converge at the poles, north and south. The parallels (as the the name suggests) never converge, but instead are like a series of stacked rings that get smaller as you approach the poles. Find some notable points on your globe for your students to recognize: Washington D.C. is at 77ºW longitude; much of the U.S./Canada border runs along the “49th parallel” (49ºN latitude); Randall Jarrell’s philosophical-geography poem “90 North” is of course about the north pole (90ºN latitude); Honolulu is at 158ºW longitude, almost on the opposite side of the world (180º E or W longitude) from the Prime Meridian (0º longitude). What is the longitude and latitude of your homeschool? 🌐

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