Browse Reference Articles
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Extrasolar planet
An extrasolar planet, or exoplanet, is a planet beyond the Solar System. As of 11 November 2006, 209 extrasolar planets have been discovered. Known exoplanets are members of planetary systems that ... > more -
Hubble Deep Field
The Hubble Deep Field (HDF) is an image of a small region of the sky, based on the results of a series of observations by the Hubble Space Telescope. The field is so small that only a few foreground ... > more -
Ceres (dwarf planet)
Ceres, also designated 1 Ceres or (1) Ceres, is the smallest dwarf planet in the Solar System and the only one located in the main asteroid belt. With a diameter of about 950 km, Ceres is by far the ... > 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 -
Cepheid variable
A Cepheid variable or Cepheid is a member of a particular class of variable stars, notable for a fairly tight correlation between their period of variability and absolute luminosity. Since the ... > more -
Near-Earth object
Near-Earth objects (NEO) are asteroids, comets and large meteoroids whose orbit intersects Earth's orbit and which may therefore pose a collision danger. Due to their size and proximity, NEOs are ... > more
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