Latitude and longitude and other fascinating stuff
Latitude and longitude and other fascinating stuff
On February 8, 2022, Statsraad Lehmkuhl sailed across the equator, the circle that divides the globe into the northern and southern hemisphere. There are more circles crossing the globe, here is the story behind them.
Imagine sticking a long rod through the globe from the North Pole to the South Pole. At the middle of the rod, in the center of the earth, attach a new rod perpendicular to the first. Grasp this rod where it protrudes from the globe, and rotate it a full circle. The globe splits in two, divided into a northern and a southern hemisphere.
The line along the split is the Equator.
Most of the Equator runs across oceans, but it divides Africa roughly in two, crosses the islands of Indonesia, and the northern part of South America. Through Brazil, Colombia - and Ecuador, which have been named after the line.
The circles of latitude
The Equator is one of the globe's five natural parallel circles, or latitudes. The other four are the Tropics and the Arctic Circles. In his report on 31 January, Captain Jens Joachim Hiorth explained the two Tropics.
- The Tropic of Cancer is roughly 23 degrees and 26 minutes north of the equator. It is characterized by the sun being at its zenith, 90 degrees on the earth's surface, when it is highest in the sky at the summer solstice. Why? Is it not at the Equator that the sun is at its zenith? This is because the earth's axis forms an angle with an imaginary line between us and the sun. The point where the sun is at its zenith, will move throughout the year between the Tropic of Cancer, and the Tropic of Capricorn which is located equally far to the south of the equator.
The sun is in the zenith above the equator twice a year, at the vernal equinox and autumnal equinox. These are the only two days of the year when the length of the day is the same on the entire globe.
The area between the Tropic of Cancer, and the Tropic of Capricorn we call, surprise, the tropics.
The Polar Circles
The Polar Circles runs 66 degrees and 33 minutes north and south of the equator. The southern one is mostly out in the ocean, but parts of it runs close to the coast of Antarctica.
The Polar Circle crosses the county of Nordland in Norway, close to the city Mo i Rana. Between the Polar Circles and the Poles there is midnight sun in summer and polar night in winter. These are the areas we call the Arctic in the north, and the Antarctic in the south.
Fun fact: The city Bodø, which is located one degree north of the Arctic Circle, has midnight sun from June 3 to July 8, a little over a month. But no polar night! The explanation is the atmosphere. The light is refracted by the air, and this effect "lifts" the sun up, so that it ends a little higher in the sky than the latitude indicates.
A nautical mile
The equator is 40,075 kilometers long. If the earth were completely spherical, the equator would be exactly twice as long as the latitude circle running at 60 degrees. But the earth is a little flattened, so there is a slight discrepancy.
If you round off the length of the equator to 40,000 kilometers, and divide it first by 360 degrees, and then by the 60 minutes of each degree, you get a familiar number; 1852 meters, one nautical mile. So, the definition of a nautical mile is the length of an arc minute at the equator.
We use knots to measure speed at sea; the number of nautical miles per hour. 20 knots is 37,040 meters per hour, a little over 37 km/h. It feels faster in a boat than in a car ...
In contrast to the latitudes, all longitudes are exactly the same length, they run from pole to pole.
Together with the latitudes, longitudes form a grid across the globe, useful when navigating. The Greek astronomer Hipparkhos got this idea first, about 150 years before our era. It is 90 degrees from the equator to each pole, and Hipparkhos divided the equator into 360 degrees. We still use his system today.
Placing the grid north to south is simple, 0 degrees is the Equator. But where to put 0 degrees east to west?
For a long time, most countries had their own so-called zero meridian, including Norway. On really old maps, the positions are given in degrees east and west of Christiania. Having a lot of slightly different grids is cumbersome, so at the International Meridian Conference in Washington in 1884, it was decided that the British zero meridian through Greenwich outside London should be used by all.
Just like the nautical mile, the meter has also been based on our globe.
France was the first country to use meters to measure length, and in 1791, they decided that one meter should be one ten-millionth of the distance from the North Pole to the equator, along the longitude running through Paris. One meter long rods made of bronze and then platinum, and finally platinum and iridium were cast as templates, and kept as standards.
In 1906 more precise definitions based on wavelengths took over. Since 1983, the length of one meter has been defined as the distance light travels in vacuum during a 1 / 299 792 458 of a second.
When Statsraad Lehmkuhl crossed the equator, a bunch of visitors came on board.
It takes a while to sail all the way south to the equator, or "the line" as sailors call it. You should have learned the skills of seamanship by then. King Neptune, the sea god in Roman mythology, has been given the job of testing the fresh sailors.
He comes on board with his entire entourage: Queen Neptune, an astronomer, a doctor, bishop, barber, herald and drabants or soldiers.
The exam ends in form of baptism, which, to quote the Norwegian Maritime Directorate, "could be a harsh ordeal". First being shaved, then submerged in not exactly clean water, and finally served "food" you would rather not eat.
Line baptisms have been organized since the 16th century, and all maritime nations have their own version. Today, it is just a nice party on board, as it was on board Statsraad Lehmkuhl.