The Gregorian Calendar

The Gregorian calendar is the calendar that is used nearly everywhere in the world. A modification of the Julian calendar, it was first proposed by the Calabrian doctor Aloysius Lilius, and was decreed by Pope Gregory XIII, for whom it was named, on 24 February 1582 via the papal bull Inter gravissimas. Its years are numbered per the perceived birth year of Jesus Christ, which is labeled the "anno Domini" era. This era was created in the 6th century by Roman monk Dionysius Exiguus.
The number of days in a Gregorian year is the average number of days per year in the time interval of 400 years of the Gregorian calendar. The Gregorian calendar was established in 1582 by the Pope Gregorio XIII and replaced the Julian calendar established by the roman emperor Julius Caesar in the year 46 B.C.
The Gregorian calendar contains regular years (with 365 days each) and leap years (with 366 days each). The rule used to decide if a year is a regular year or a leap year is quite simple. The year is a leap year if it is a multiple of 4, the centennial years excluded. A centennial year will be a leap year if it is a multiple of 400. So the most recent leap years we had are 2000, 2004 and 2008. Note that 2000 is a leap year only because it is a multiple of 400. The year 1900 was not a leap year. The same can be said of the year 2100 (despite the fact they are multiples of 4). The next leap year will happen in 2012

The South Atlantic Magnetic Anomaly - SAMA

The South Atlantic Magnetic Anomaly (SAMA) refers to the area where the Earth's inner Van Allen radiation belt comes closest to the Earth's surface. This leads to an increased flux of energetic particles in this region and exposes orbiting satellites to higher than usual levels of radiation. The effect is caused by the non-concentricity of the Earth and its magnetic dipole. The SAMA is the near-Earth region where the Earth´s magnetic field is weakest.
The Van Allen radiation belts are symmetric with the Earth's magnetic axis, which is tilted with respect to the Earth's rotational axis by an angle of ~11 degrees. The intersection between the magnetic and rotation axis of the Earth is located ~500 kilometers (300miles) more to the North, above the centre of the Earth. Because of this tilt and translation, the inner Van Allen belt is closest to the Earth's surface over the South Atlantic Ocean and farthest from the Earth's surface over the North Pacific Ocean
The illustration shows a cross-sectional view of the Van Allen radiation belts, noting the point where the South Atlantic Anomaly occurs
The South Atlantic Magnetic Anomaly is of great significance to astronomical satellites and other spacecraft that orbit the Earth at several hundred kilometers altitude; these orbits take satellites through the anomaly periodically, exposing them to several minutes of strong radiation, caused by the trapped protons in the inner Van Allen belt, each time. The International Space Station, orbiting with an inclination of 51.6°, requires extra shielding to deal with this problem. The Hubble Telescope does not take observations while passing through the SAMA. Astronauts are also affected by this region which is said to be the cause of peculiar 'shooting stars' seen in the visual field of astronauts.
The shape of the SAMA changes over time. Since its initial discovery in 1958, the southern limits of the SAMA have remained roughly constant while a long-term expansion has been measured to the northwest, the north, the northeast, and the east. Additionally, the shape and particle density of the SAMA varies on a diurnal basis, with greatest particle density corresponding roughly to local noon. At an altitude of approximately 500 km (300 mi), the SAMA spans from -50° to 0° geographic latitude and from -90° to +40° longitude. The highest intensity portion of the SAMA drifts to the west at a speed of about 0.3 degrees per year. The drift rate of the SAA is very close to the rotation differential between the Earth´s core and its surface, estimated to be between 0.3 and 0.5 degrees per year.

The Earth´s Magnetosphere

The magnetosphere of Earth is a region in space whose shape is determined by the extent of Earth's internal magnetic field, the solar wind plasma, and the interplanetary magnetic field (IMF). In the magnetosphere, a mix of free ions and electrons from both the solar wind and the Earth's ionosphere is confined by electromagnetic forces that are much stronger than gravity and collisions.
In spite of its name, the magnetosphere is distinctly non-spherical. All known planetary magnetospheres in the solar system possess more of an oval tear-drop shape due to the effects of the solar wind.
On the side facing the Sun, the distance to its boundary (which varies with solar wind intensity) is about 70,000 km (10-12 Earth radii or RE, where 1 RE=6371 km; unless otherwise noted, all distances here are from the Earth's center). The boundary of the magnetosphere ("magnetopause") is roughly bullet shaped, about 15 RE abreast of Earth and on the night side (in the "magnetotail" or "geotail") approaching a cylinder with a radius 20-25 RE. The tail region stretches well past 200 RE, and the way it ends is not well-known.