Wednesday, 7 July 2010

Nautical miscellany

For those that have asked what the numbers mean at the end of my posts now we are under way, they give our position in latitude and longitude. You can use these numbers to "see" exactly where we are using Google Earth.

51 51.60'N

gives our latitude and means that we are 51 degrees north of the equator (if you take the angle from the centre of the earth) plus 51 decimal 60 minutes. There are 60 minutes in each degree.

One minute equals one sea mile. This means that the length of a sea mile varies according to how far south or north of the equator you are. For most practical purposes one sea mile equals the internationally agreed nautical mile of 1852 metres. Prior to this agreement in 1929, different countries had slightly different definitions.

00 09.767'W

gives our longitude and indicates that we are west of the Greenwich Meridian by 9 decimal 767 minutes. The calculation of longitude was a struggle for centuries and involved many great scientific minds. Amerigo Vespucci on his trips to the New World was perhaps the first to profer a workable solution, by noting the time difference between observed happenings in the sky, eg planet movements, and times listed in an almanac for home. But it was not until the development of an accurate ship's chronometer by John Harrison, an english clockmaker, that position could be accurately determined.

The story is a fascinating one and worth spending some time looking into.

No doubt there will be more stuff as we encounter more days where the weather keeps us in port.

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