The Terrestrial Space
The Greek mathematician Eratosthenes, towards 240 BC, was the first to evaluate the circumference of the terrestrial globe. He used the following method. Knowing that at noon the same day of the year the sun hit to the bottom of a well in Aswan, Egypt but produced a shade on an obelisk in Alexandria located to the north, he measured the distance between these two points. With the angle of the shade on the obelisk and the distance he then made an approximate evaluation of the terrestrial circumference, which was only within 15% of the real size.
| Surface | 510,900,000 km2 |
| Equatorial diameter | 12,746.32 km |
| Polar diameter | 12,713.55 km |
| Equatorial circumference | 40,075.15 km |
| Polar circumference | 39,940.80 km |
| Rotation | The earth’s movement around its polar axe (24 hours) |
| Revolution | The earth’s movement around the sun (365 days and ¼) |
| Earth’s axis | 23 ½ degrees |
| Solstice | Summer: 21-22 June. Winter: 22-23 December. |
| Equinox | Spring: 20-21 March. Fall: 22-23 September. |
| Tropic of Cancer | Summer solstice, 23 ½ degrees north. |
| Tropic of Capricorn | Winter solstice, 23 ½ degrees south. |
| Meridian | Half circle having extremities at each of the poles. |
| Parallel | Circle produced on a parallel plan to the equator. |
| Latitude | Arc measured in degrees of a meridian according to the distance from the equator (0-90). |
| Longitude | Arc measured in degrees of a parallel between the place and the meridian of origin, Greenwich (0-180). |
| Co-ordinate | A longitude and latitude pair. |