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.

Type to find tags:
× 2 × 13
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.
× 18
Questions regarding the universe shortly after it's formation
× 113
Questions regarding the planet on which humans live, the third planet from the sun.
× 20
Questions about solar system planets/moons and exoplanets that exhibit similar features to the Earth.
× 4
Questions about orbits with high eccentricities, which deviate greatly from perfect circles.
× 3 × 2
× 3
× 2
Questions about the speed at which an object can go to a point at infinity while ending at rest.
× 4
Questions about Europa, a moon of Jupiter with a planet-wide ocean under a thick ice crust.
× 83
Questions regarding planets that lie outside the Solar System.
× 38
Questions about the increase with time of distance between two distant points in the Universe.
× 5 × 2
× 2
× 16
For questions about objects or phenomena outside Earth, generally on other planets.
× 4
about the lack of evidence for alien life, despite the growing evidence that suitable planets are reasonably plentiful.
× 24
Questions about the dynamical processes leading to the assembling of a celestial object.
× 47
Questions involving basic astronomical concepts or information.
× 19
Questions regarding interactions between galaxies or between major parts of a galaxy.
× 2
× 124
Questions regarding systems of large numbers of stars held together by gravity.
× 10
Questions regarding the inner portion of a galaxy; in the Milky Way, this is the area around Sagittarius A*.
× 13
Questions regarding gravitationally bound systems of hundreds to thousands of galaxies as well as interactions between such systems.
× 2
× 7 × 7
Questions regarding matter in its gaseous state, and how it behaves in astronomy (e.g. forming stars in giant molecular clouds).
× 18
Questions regarding massive planets composed of layers of gases, such as hydrogen and helium, surrounding a solid/liquid core.
× 49
Questions about relativistic theory of gravity. General relativity describes gravity as a geometrical property of space and time.
× 2
× 10
Questions related to earth processes or related processes and principles.
× 4
Questions about large, dense, massive collections of stars orbiting galaxies, thought to have formed in the early universe.