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Geomagnetic reversal
A geomagnetic reversal is a change in the orientation of Earth's magnetic field such that the positions of magnetic north and magnetic south become interchanged. The Earth's magnetic north pole is ... > more -
Aurora (astronomy)
The aurora is a glow observed in the night sky, usually in the polar zone. It is also known as "northern lights" or "aurora borealis," which is Latin for "northern dawn" since in Europe especially, ... > more -
Comet Hale-Bopp
Comet Hale-Bopp was probably the most widely observed comet of the 20th century, and one of the brightest seen for many decades. It was visible to the naked eye for a record 18 months, twice as long ... > more -
Jupiter's natural satellites
Jupiter has 63 known natural satellites. Although claims are made for the observation of one of Jupiter's moons by Chinese astronomer Gan De in 364 BC, the first certain observations of Jupiter's ... > more -
Deimos (moon)
Deimos is probably an asteroid that was perturbed by Jupiter into an orbit that allowed it to be captured by Mars, though this hypothesis is still in some dispute. Like most bodies of its size, ... > more -
Definition of planet
The definition of "planet" has for some time been the subject of intense debate. Although the word dates back thousands of years, no officially decreed scientific definition of "planet" existed ... > more
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