Friday, 8 February 2008

A journey through the centre of the earth

I have just read the web diary account of yesterday and it seems that I wasn't the only one having difficulty with the roads! However, according to the tracker, Mark is now about 45 miles north of Madrid and bound for Burgos tomorrow. He has stopped tonight just south of the border with the province of Spain called Segovia.

The significance of Madrid, apart from it being a major milestone through Spain, is that it is one of two antipodal points along Mark's route. According to the Guinness criteria, which you can read under the route tab on , the route for a global circumnavigation must include two antipodal points.

That is actually harder to achieve than it sounds as there are fewer antipodal points on land than you might imagine. Antipodes are diametrically opposite one another i.e. they can be linked by a line going through the centre of the earth. However, most of the earth's land surfaces have ocean at their antipodes, this being a consequence of most land being in the northern hemisphere. This must have been a significant factor when planning the route. The globe shows how few the options actually were .....if Mark was to avoid Antarctica, the islands of Indonesia, the Amazon basin, Outer Mongolia, the Sahara, some Pacific islands and Siberia! Small wonder that he opted for New Zealand and Spain.
Within New Zealand and Spain, there are three pairs of antipodal cities - Hamilton and Cordoba, Auckland and Malaga and Wellington and Madrid. Malaga and Cordoba would have taken Mark too far south in Spain, leaving Wellington and Madrid as the obvious choice.

However, the Guinness rules are not just as simple as that. The longitude values have to add up to 180 degrees and the latitude values should be the same. If there is a difference on either or both, the total difference should not be more than 5 degrees. Let's check it out.....

If we round up to degrees, minutes and seconds (bearing in mind that there are 60 seconds in a minute and 60 minutes in a degree) , the latitude difference is 52' 6" - under 1 degree. The longitude values add up to 178 degrees 28' 44" giving a difference from 180 degrees of 1 degree 31' 16". The total 'error' is therefore just over 2 degrees - well within the 5 degrees allowed by the Guinness criteria.

Now, there is a much more fun way of doing antipodal points.....
If you click on Holey Moley, you can find out!

Having taken a slightly different tack in today's posting, I think I might take the liberty of bypassing Madrid and fast forwarding to the last part of today's journey which took Mark into the foothills of the Sierra de Guadarrama. The highest peaks in this range rise to around 2500m (hence the snow as in the Sierra de Gredos which we saw yesterday) but his route tomorrow morning will take him across a col at around 1500m. However, in order to reach there, there were two tough climbs today. This is because, as you can see from the map below the highest ground forms a V shaped ridge with an intermontane valley. So, having ascended the first ridge (Sierra de la Cabrera) and dropped down into the valley, it would have been all uphill again!
Incidentally, the underlying geology of this region is granite, as witnessed by a number of granite quarries such as this one in the vicinity of la Cabrera ....

...and below some weathered granite rocks in the Sierra de Cabrera borrowed from Flickr. Because of the way in which granite weathers along its joints, it gives rise to these very distinctive 'tor' landforms wherever it occurs in the world. The view below could be Dartmoor or Ben Macdhui .... blue sky? ... perhaps not!Legislation to designate a large part of the Sierra de Guadarrama as Spain's 15th national park is likely to be passed this year and one of the promotional videos (by an organisation with an unfortunate abbreviation) for that proposal is included below .....

If the embedded video does not play, click here to view it in its original location.

Mark has ended the day today at around 1200m - high enough to produce a cooler microclimatic zone. These images, all borrowed from Flickr and taken within a few miles of where Mark is this evening, give an impression of the surrounding landscape ......

It could be quite cool up there!

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