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Halfway point

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BigStu
612899.  Mon Sep 14, 2009 2:52 pm Reply with quote

Was discussing this in the pub the other night, thought it would be well suited to here...

What latitude would you be at if you're halfway from the equator to the North Pole?

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Buzzer for anyone saying "45 degrees North". The Earth isn't spherical, so the 45th parallel is actually 10 miles South of the halfway point.

This annoys me every time I drive along Interstate 5, just South of Portland, where there's a sign at 45N saying it's the halfway point...

The 45th parallel is, however, a good jumping off point to some Quite Interesting ramblings, since it runs through the top end of Yellowstone National Park...

 
mckeonj
612921.  Mon Sep 14, 2009 3:12 pm Reply with quote

I presume that the explanation for this is that the halfway point is along the Great Circle.

 
Jenny
612927.  Mon Sep 14, 2009 3:19 pm Reply with quote

That would be Portland, Oregon, I presume? The interstate nearest to me, in the neighbourhood of Portland, Maine, is I95. I don't think there's a 'halfway point' marker along it though - not between here and Boston at any rate.

 
mckeonj
612932.  Mon Sep 14, 2009 3:32 pm Reply with quote

According to GoogleEarth, Halfway Point is in Canada

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<Placemark>
   <name>Halfway Point, Humber Arm South, NL, Canada</name>
   <open>1</open>
   <address>Halfway Point, Humber Arm South, NL, Canada</address>
   <LookAt>
      <longitude>-58.093395</longitude>
      <latitude>48.988281</latitude>
      <altitude>0</altitude>
      <range>1739.79541</range>
      <tilt>0</tilt>
      <heading>0</heading>
   </LookAt>
   <styleUrl>http://maps.google.com/maps?q=Halfway+Point,+Humber+Arm+South,+Division+No.+5,+Newfoundland+and+Labrador,+Canada&amp;sll=53,-8&amp;sspn=109.258,360&amp;ie=UTF8&amp;v=2.2&amp;cv=5.0.11733.9347&amp;hl=en&amp;ct=clnk&amp;cd=1&amp;geocode=FXmA6wIdrZCJ_A&amp;split=0&amp;output=kml&amp;ge_fileext=.kml#default+nicon=http://maps.google.com/mapfiles/kml/pal3/icon60.png+hicon=http://maps.google.com/mapfiles/kml/pal3/icon52.png</styleUrl>
   <Point>
      <coordinates>-58.093395,48.98828099999999,0</coordinates>
   </Point>
</Placemark>
</kml>

 
suze
612944.  Mon Sep 14, 2009 3:50 pm Reply with quote

I'm confused here. I understand that the Earth is not a perfect sphere - but why does that mean that 45 N is not half way between the Equator and the North Pole?

If it is not, that would imply that not all degrees of latitude occupy the same number of miles north to south (69 miles / 111 kilometers, or so I was taught in school). Which would be fine, except that I'd always imagined that they were defined so to be (at 0 longitude, if it makes a difference).

In which case, which degrees of latitude are actually "bigger" than that? Is it the ones nearest the equator, or the ones nearest the Poles?

 
Ion Zone
612948.  Mon Sep 14, 2009 3:55 pm Reply with quote

Quote:
since it runs through the top end of Yellowstone National Park...


Which is a super-volcano.

 
BigStu
612949.  Mon Sep 14, 2009 3:56 pm Reply with quote

There is also the "city" of Halfway, Oregon (population 337). Which is almost exactly on the halfway point, within a mile or two. But it was actually named that because it was halfway between the even smaller "city" of Pine, and the gold-mining now ghost town of Cornucopia; the name has nothing to do with its geographical significance.

It's also mildly famous for the fact that in 2000, the town officially changed its name to half.com, in a sponsorship deal with an internet company.

 
BigStu
612954.  Mon Sep 14, 2009 4:01 pm Reply with quote

suze - the latitudes are defined by the angle you would get if you cut a cross-section through the Earth, in a triangle whose other corners are at the equator and at the center. Since the globe is squashed at the top and bottom, the 'surface distance' (discounting hills etc) between adjacent degree lines is very slightly longer near the poles. Less than a mile difference though, from mental calculations, so your 69 mile figure may well still be right after rounding errors...

 
Ion Zone
612966.  Mon Sep 14, 2009 4:15 pm Reply with quote

Get your maths teacher with his wheel on a stick. :}

 
mckeonj
613051.  Mon Sep 14, 2009 6:14 pm Reply with quote

There is in England a town called Meriden, which means halfway or middle.

 
suze
613054.  Mon Sep 14, 2009 7:07 pm Reply with quote

Looking on a map, the halfway-ness of Meriden seems to be as between Coventry and Solihull.

There are a few places in the UK called Halfway as well. We discussed this once before and found four - one in South Yorkshire (halfway between Sheffield and Chesterfield), two near Glasgow (Glasgow and Hamilton, and Glasgow and Paisley), and one in Kent (Sheerness and somewhere else).

 
Moosh
613064.  Mon Sep 14, 2009 7:44 pm Reply with quote

Meriden also claims to be the geographical centre of England, and has done for at least 500 years.

On the other hand, so does Leamington Spa, Haltwhistle, Dunsop Bridge and Weedon Bec.

 
Peregrine Arkwright
613177.  Tue Sep 15, 2009 4:51 am Reply with quote

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Halfways
There are plenty of places called Halfway in South Wales, and for the life of me I can't work out where they are halfway between. One of them consists of about four nondescript houses a few miles out of Llandovery en route to Brecon.

Chesterfield used to claim to be the mid-point of England but I believe the Ordnance Survey now place it some way south of there.

Is there anywhere that claims to be the mid-point of the USA?

Peregrine Arkwright
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Celebaelin
613193.  Tue Sep 15, 2009 5:47 am Reply with quote

Re Meriden the rumour has it that if you get an outline of mainland Britain
and locate the centre of gravity (hang it from any three points on the
coastline and take a plumb line to it and see where the three lines cross)
then it will be at Meriden. How accurate this is is another question but it's
not far away - I guess you'd need quite a big cut out to do it with any
accuracy but we did it at primary school and it seems to be about right.

 
suze
613331.  Tue Sep 15, 2009 11:32 am Reply with quote

For the answer to that question to be Meriden - or somewhere reasonably close thereto - wouldn't we have to consider purely mainland England rather than Great Britain?

The question of where the centre of Great Britain is appears to be controversial - see this article from the BBC - but it's clearly somewhat further north.

 

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