A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.

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Questions regarding matter at densities so high that gravitational contraction is countered by the Pauli exclusion principle.
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A measure of the ratio of an object's mass with its volume.
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Questions regarding the amount of space between two objects, the units, or measurement thereof.
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a relatively inexpensive Newtonian telescope, in which the tube assembly slips freely in the lower base.
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Questions regarding bodies smaller than planets but larger than other bodies, that do not meet at least one of the IAU's criteria for being a planet.
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Questions regarding the universe shortly after it's formation
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Questions regarding the planet on which humans live, the third planet from the sun.
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Questions about solar system planets/moons and exoplanets that exhibit similar features to the Earth.
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Questions about orbits with high eccentricities, which deviate greatly from perfect circles.
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Questions about the speed at which an object can go to a point at infinity while ending at rest.
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Questions about Europa, a moon of Jupiter with a planet-wide ocean under a thick ice crust.
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Questions regarding planets that lie outside the Solar System.
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Questions about the increase with time of distance between two distant points in the Universe.
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For questions about objects or phenomena outside Earth, generally on other planets.
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Questions regarding the future and ultimate fate of the Universe, including the heat death, Big Freeze, Big Rip, or Big Crunch.
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about the lack of evidence for alien life, despite the growing evidence that suitable planets are reasonably plentiful.
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