Question regarding hemispheres, direction and maps.

August 25, 2004 10:40 AM

Question regarding hemispheres, direction and maps.

Ok. So if I travel far enough East, eventually, I am heading West because of geography terms, right? But in the abstract, I would still be heading east in the sense of right of North. So this confuses me. I am guessing the distinction exists for a geographical reason. But I am not sure why analytically hemispheres are necessary.

If I have a compass in my hand and keep walking East, at any point does the compass rotate where I think I would be walking West?

So, the North Pole is at 90 degrees north, but which side is 100 degrees? I was told that you only think of North of the equator in terms of 90 degrees. But, you think of East/West of the equator in terms of 180 degrees from the prime merdian. What gives? Why the difference? It is still half a globe.

Does it make any sense to say that NY is east of LA and that LA is east of NY? Does it make any sense to say that Canada is south of Mexico?

Is there a simple explanation that explains all this confusion?

posted by Seth to education (14 comments total)

Ok. So if I travel far enough East, eventually, I am heading West because of geography terms, right?

No.

But in the abstract, I would still be heading east in the sense of right of North.

That is right...not just in the sense of "right of North," but in every sense.

If I have a compass in my hand and keep walking East, at any point does the compass rotate where I think I would be walking West?

Barring the complication that magnetic north does not coincide with geographic north (and in some places the two are significantly different), no.

So, the North Pole is at 90 degrees north, but which side is 100 degrees? I was told that you only think of North of the equator in terms of 90 degrees. But, you think of East/West of the equator in terms of 180 degrees from the prime merdian. What gives? Why the difference? It is still half a globe.

Latitude can be thought of as the angle with your location at one point, the center of the earth as the angle, and the equatorial plane as the other side of the angle. Longitude is the angle between you and a half-plane passing through the poles, the center of the earth, and Greenwich, England. Because latitude is the angle to a plane, it cannot be more than 90 degrees; longitude is the angle to a half-plane, so it can be up to 180 degrees.

Does it make any sense to say that NY is east of LA and that LA is east of NY?

In a sense, yes. You can travel (roughly) east from LA and arrive in New York in 3000 miles or so. You can travel (roughly) east from New York and arrive in LA after about 14000 miles. When we say that LA is west of New York, you can think of that as meaning that the westerly route from New York to LA is shorter than the easterly route from New York to LA.

Does it make any sense to say that Canada is south of Mexico?

No, that is not true in any sense. East and West are fundamentally different than North and South. You can go east, and keep going east forever, because you're going around in circles. There's no "end" to going east or west. But if you go North, eventually you'll reach the North Pole, and you can't go any further north than that. At the North Pole, all directions are south.
posted by DevilsAdvocate at 10:54 AM on August 25, 2004

AskMetafilter: all directions are south.
posted by Eamon at 11:01 AM on August 25, 2004

P.S. as another way of thinking how east and west are different than north and south, you might want to think a bit about why there are north and south poles, but no east or west poles.
posted by DevilsAdvocate at 11:01 AM on August 25, 2004

As long as you're walking East, you're never going to be going West. You can walk around the Earth 27 times and you'll always be going East. Reverse direction and you'll be going West.

Leaving out the case of magnetic declination (Magnetic North is not the same as True North), as long as you were walking East the compass would never move. It would always be pointing North.

NY is East of LA. LA is West of NY. I tend to think the cutoff point is 180 degrees or an ocean.

North and South exists because of the Earth's magnetic feild. There is no "east pole" or "west pole"

On preview: What DA said.
posted by bondcliff at 11:02 AM on August 25, 2004

Basically, we use spherical coordinates to describe our position on (in, or around) the planet.

In case all this is disappointingly mundane, think about this instead: if you take bondcliff's advice and walk around the Earth 27 times going east, you'll believe that the date is almost a month later than it really is. Astronauts orbiting the Earth at high speeds don't have to worry about this. Why?
posted by Eamon at 12:00 PM on August 25, 2004

The Eastern and Western hemisphere designations confuse the straightforwardness of the "moving east gets you east" assertion, as does the International Dateline in a "What day is it?" sense. [link answers Eamon's question]
posted by jessamyn at 1:07 PM on August 25, 2004

Reminds me of a riddle, which sort of applies: how far can a dog run into a forest? Halfway, because after that he's running out of it.
posted by hootch at 1:23 PM on August 25, 2004

This thread enabled to look for, and find, and answer to a question I had which is, what Time on earth do astronauts attach themselves to? Is it GMT, or is it the local time of their contacts in Mission Control. From this article, it appears to be GMT>

Another Geography riddle: If you always go NorthWest, will you ever reach the North pole?? If not, isnt this a way of going Northwards forever? ;)
posted by vacapinta at 1:38 PM on August 25, 2004

If you always go NorthWest, will you ever reach the North pole??

Zeno?

Is space continuous?
posted by trharlan at 2:59 PM on August 25, 2004

If you always go NorthWest, will you ever reach the North pole??

Yes, you will, although it may not be intuitively obvious. You will be following a rhumb line--and although you'll wind around the pole an infinite number of times, you'll still reach it in a finite distance.
posted by DevilsAdvocate at 3:15 PM on August 25, 2004

Hey Seth, now that you've got that one 'splained, you can chew on this:

Why do mirrors invert left and right, but not up and down?
posted by Wet Spot at 5:36 PM on August 25, 2004

Mirrors don't invert left and right. They invert front and back.
posted by SPrintF at 6:58 PM on August 25, 2004

Mirrors don't invert anything. They just reflect (obviously).
posted by ZippityBuddha at 4:18 AM on August 26, 2004

Why are our eyes left and right, but not up and down?
posted by Songdog at 10:18 AM on August 26, 2004