Part 1
In this video, the rotation of Earth, the difference between latitudes and longitudes and the tropical and polar circles are described.
To begin with, the Earth spins around its axis. This happens at a tilt of 23.4°. The axis is an imaginary line that runs through the planet. The Geographic north pole, or simply north pole, is the point in the upper half of the Earth where the axis of rotation meets the surface. Similarly, the South pole is the point in the lower half of the Earth where the same axis meets the surface.
Latitude lines are horizontal lines that run from 0* at the equator, all the way up to + and – 90° at the poles. To specify the location of a place, the first coordinate is the latitude which specifies where the place is located within a vertical space. On the other hand, longitudinal lines are vertical lines that run along with the Earth. It is also used to denote the position and is the second coordinate in specifying the location. It is also measured in degrees. At Greenwich, the longitude measures 0° and runs up to 180° in both East and West directions.
The difference between the two types of imaginary lines is that latitudinal lines are parallel and equally spaced lines that never cross each other. While longitudinal lines meet at the poles and change spacing throughout the length of the lines. These are visually represented and explained in this video.
There are five important latitudinal lines. These divide the earth into different geographical zones which have similar temperature conditions. The 0° latitude is the equator. The tropical circles which are the tropic of Cancer and Capricorn are northernmost and southernmost latitudes respectively where the Sun can be seen directly overhead. And finally, the Arctic and Antarctic poles are locations where one day a year the sun doesn’t set, and another day 6 months later, it doesn’t rise.
Part 2
In this second video, the concept of meridians is explained, including what they are used for, and what is so special about the spot in Oude Pekala.
A meridian is another word for a line of longitude. The 0th meridian or prime meridian runs through Greenwich from the north to the south pole. If we would continue this line on the other side of the world from the south to the north pole, we have the 180th meridian. These two meridians form a Great circle. A Great circle is any circle which goes from pole to pole and back. So the first and 181st meridian also form a great circle.
Meridians were and still are very important as they are used for navigation. Lines of latitude and meridians form a grid. If you have a point on the earth, you can specify its location using this grid. We now give the lines in the image a number from 1 to 5. It becomes clear that the red dot has a longitude of approximately 3.5 and a latitude of 2.7 or so. This principle was used in map making and navigation.
But there was a little problem in making universal maps, namely defining a zero point. Every country wants it to be at some important point for them, such as their capital for example. So in one country, the coordinates of a place could be 3.5 and 2.7, but in another country, it could be 44.5 and 57.7. This is not that practical as you can see, because this would make a map from Greece completely useless in the Netherlands, for example. So they decided to take a universal zero point in Greenwich. The Earth was then divided into 360 of these meridians. If you would go 7 meridians east of Greenwich, you would end up with a meridian that runs through the Province of Groningen. More precisely, right through the specific point in Oude Pekela.
To get a better idea of how big the spacing is between meridians, a few places with their longitude have been listed in the video. For example, Greenwich lays on exactly 0, but Amsterdam has a longitude of 4.5 and Berlin one of 13.3. If we go even further east we get St. Petersburg on 30.1.