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Impact crater
An impact crater is a circular depression on a surface, usually referring to a planet, moon, asteroid, or other celestial body, caused by a collision of a smaller body (meteor) with the ... > more -
Near-Earth asteroid
Near-Earth asteroids (NEAs) are asteroids whose orbits are close to Earth's orbit. Some NEAs' orbits intersect Earth's so they pose a collision danger. On the other hand, NEAs are most easily ... > more -
European Space Agency
The European Space Agency (ESA), established in 1975, is an inter-governmental organisation dedicated to exploration of space with currently 17 member states. ESA has ambitious space plans that may ... > more -
Andromeda Galaxy
TThe Andromeda Galaxy (also known as Messier 31, M31, or NGC 224; older texts often called it the Andromeda Nebula) is a spiral galaxy approximately 2.5 million light-years away in the constellation ... > more -
Geosynchronous orbit
A geosynchronous orbit is a geocentric orbit that has the same orbital period as the sidereal rotation period of the Earth. It has a semi-major axis of 42,164 km (26,200 miles). In the special case ... > more -
Interstellar medium
The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. Whilst the ISM refers to the matter (interstellar matter, also abbreviated ... > more -
Van Allen radiation belt
The Van Allen radiation belt is a torus of energetic charged particles (i.e. a plasma) around Earth, trapped by Earth's magnetic field. When the belts "overload", particles strike the upper ... > more
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