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.
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 the planet on which humans live; the third planet from the Sun.
Questions about solar system planets/moons and exoplanets that exhibit similar features to the Earth.
Questions about orbits with high eccentricities, which deviate greatly from perfect circles.
Questions regarding a binary (or more) star system where one star eclipses another, causing a dip in brightness.
Questions regarding the plane containing the orbit of the Earth around the Sun.
Questions about the upcoming European Extremely Large Telescope.
Questions about a certain range of frequencies of electromagnetic radiation, given e.g. as wavelengths or wavenumbers. Consider using the tag "wavelength" as well.
Questions on how frequent certain chemical elements are on or in a celestial object.
Questions about the sixth largest moon of Saturn.
Questions about the predicted positions of an object in space, like another planet, comet, or asteroid.
Questions about the moment when the Sun's declination is zero. A less strict definition is the day when the day and night are the same length.
Questions related to missions carried out by the European Space Agency
Questions about the speed at which an object can go to a point at infinity while ending at rest.
Questions asking for approximate results by making an educated, reasonable guess based on the information given.
Questions about Europa, a moon of Jupiter with a planet-wide ocean under a thick ice crust.
An event horizon is the notion of a distance away from the gravitational center of mass of a black hole. Observers outside of the event horizon can escape however any object including light which app…
Questions about the Event Horizon Telescope, or EHT.
Questions regarding planets that lie outside the Solar System.
Questions regarding non-baryonic matter, most notably, matter with negative mass or imaginary mass, such as tachyons.
Questions about the increase with time of distance between two distant points in the Universe.
for questions regarding the dimming of light from distant objects when it passes through interstellar dust and gas clouds. This is not for questions about extinctions of species on Earth or other …