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.
Question on time dilation, a physics concept about changes in the passage of time, caused by general relativity.
Questions regarding the universe shortly after its formation, up to the CMB or even as far as the formation of the first galaxies
Questions regarding an event where the Earth goes between the Sun and the Moon and casts a shadow on the Moon.
Questions regarding one of the two main angles(coordinates) of an object perceived by an observer on Earth.
Questions regarding the process of assigning an identifying set of characters to an astronomical object.
Questions regarding structures designed to aid in the observation of astronomical objects.
Questions about sub-stellar objects that are like stars but never achieve permanent nuclear fusion because they are too low-mass.
Questions regarding simulations for an n-body problem.
Questions regarding one of the three forms of space debris, this case a chunk of debris that survives its passage through the atmosphere and lands on a planet intact.
Questions about stellar objects which are too faint to observe with faint naked eye or even too far away for Earth-bound telescopes.
Questions regarding objects whose orbits bring them in close proximity to Earth, posing potential hazard.
Questions about rings of debris that encircle the equatorial regions of some planets.
Questions about the "Goldilocks Zone" around a parent star where conditions are just right for the potential of life developing.
Questions about the measuring the position of stars, and the techniques used to do this.
Questions asking "What is a good book about X?" or more generally, "What should I read to learn about X?", typically where there is not a single authoritative reference. Also requests for multimedia,…
Questions regarding Albert Einstein's theory that posits, among other things, the equivalence of mass and energy.
Questions regarding disks of gas, dust, and plasma around a central object, such as a black hole, which takes in the matter.
Questions about the NASA space observatory famous for finding potentially habitable exoplanets. Do not use this tag for questions about Johannes Kepler.
Questions regarding a phenomenon when an object has an orbital period that is equal to its rotational period due to gravitational tidal forces.
Questions about the predicted positions of an object in space, like another planet, comet, or asteroid.
Questions regarding the plane containing the orbit of the Earth around the Sun.
Questions regarding two objects colliding into each other with considerable force.
Questions about particulate matter found between stars, not to be confused with gas or ionised plasma. For planetary dust storms, use [dust-storm].
Questions about observations performed without the aid of any optical instrument.
Questions about the Hubble constant, the constant factor of the rate of expansion in the universe
Use for questions about standards of measurement used for different types of quantities, and for conversions between units.
Questions about the apparent displacement of a celestial body with respect to its background when observed along two different lines of sight.
Questions regarding a substance that takes up space, has volume, and has mass. Matter usually occurs in 5 forms, namely plasma, gas, liquid, solid, and bose-einstein condensate.
Questions about astronomical observations which involve superimposing waves received by multiple, physically separated, receivers to obtain higher angular resolution.
Questions about streams of plasma released from the Sun or other stars (stellar winds).
Questions about the ability of any image-forming device to distinguish small details of an object.
Questions regarding the theory of gravity as proposed by Newton, in which the force of gravity depends only on the mass of bodies, a constant, and the distance between them, and depends on one equatio…
Questions regarding Neptune, the 8th and furthest major planet orbiting Earth's sun.
Questions about reflecting telescopes using a concave primary mirror and a flat diagonal secondary mirror.