The Equator is a very definite unarbitrary and invariable mark, therefore we can in no uncertain terms refer to a Northern Hemisphere and a Southern Hemisphere.
But do the terms Western Hemisphere and Eastern Hemisphere have any definite, useful, practical applications?
Of course the measurement of longitude itself is important. It isn’t terribly important which meridians are chosen as prime/international date line, so long as you select one and stay with it. I do think that it’s more convenient to have put the international date line in mid-ocean, as has been done, but it really could have been anywhere.
As Natto Guy said, the meridians that you pick to divide the world into two hemispheres are pretty much arbitrary, so long as they’re 180 degrees opposite each other – 90 east and 90 west would be equally valid as 0 and 180.
The useful thing about the Prime and 180th meridians is that with minimal jogging of the lines, it’s possible to create a set of hemispheres in which complete land masses and their ancillary offshore islands fall in one or the other as a whole. While there is no formally defined line shifting from 0 degrees the way the International Date Line does from 180, a little simple work with a staightedge to leave the British Isles and Iceland, the French coast and Iberian Peninsula, and the West African bulge in the Eastern Hemisphere, akin to the jogs in the IDL, will produce meaningful results.
Well, yes, in as much as if you are specifying a location using latitude and longitude, you need to specify E or W (or + or -) to get an unambiguous result.
Check out this page, which shows the locations entered by visitors to Heavens Above, a cool astronomy site. See the perfect mirror image of the USA floating in Central Asia? That’s what happens if you mix up East and West :smack:
As the posts have pointed out, arbitrary != meaningless. It’s arbitrary that we stop at red lights and go at green instead of vice versa, but it’s nonetheless critically important that everyone know that rule.
–Cliffy
I checked out that webpage. If you enter as an anonymous user, and do a search on the United States, and then enter your hometown, you will be shown a list of towns that match the name you entered. This list displays the longitude and latitude of each location, with the longitude correctly displayed as a negative number.
However, when you click on a specific town in the list to choose it, it then displays the longitude and latitude with the longitude expressed as a positive number.
What I’m saying is, it may not be Americans who are entering the wrong longitudes, unless the site and its database admins are American, that is.
It could be Yank visitors. I am more likely to think in terms of 81°40’40"W than I am to think of -81°40’40" (I get it right more often when using decimal coordinates, -81.6666).
I also notice, however, that the Atlantic Ocean has quite a few European visitors.
Are you sure? I just tried that. I chose United States, then off the top of my head I typed in “Evanston”. Then I chose “Evanston, Illinois” (Lat 42.041 Long -87.690).
When I clicked on it, the lat and long in the address bar were correct: http://www.heavens-above.com/main.asp?Loc=Evanston&Lat=42.041&Lng=-87.690&Alt=185&TZ=CST
D’oh- upon reading tomndebb’s post and your follow-up, I see that they are merely presenting the coordinates with the compass directions, instead of using decimals.
Well, I’ve always wanted to visit Central Asia…