![]() Hera wakes up while breastfeeding and then realizes she is nursing an unknown baby: she pushes the baby away, some of her milk spills, and it produces the band of light known as the Milky Way. ![]() In Greek mythology, Zeus places his son born by a mortal woman, the infant Heracles, on Hera's breast while she is asleep so the baby will drink her divine milk and thus become immortal. The word galaxy was borrowed via French and Medieval Latin from the Greek term for the Milky Way, galaxías (kúklos) γαλαξίας ( κύκλος) 'milky (circle)', named after its appearance as a milky band of light in the sky. 6.2 Effective radius (half-light) and its variations.Both the Local Group and the Virgo Supercluster are contained in a much larger cosmic structure named Laniakea. At the largest scale, these associations are generally arranged into sheets and filaments surrounded by immense voids. The group is part of the Virgo Supercluster. The Milky Way is part of the Local Group, which it dominates along with Andromeda Galaxy. Most galaxies are gravitationally organized into groups, clusters and superclusters. The space between galaxies is filled with a tenuous gas (the intergalactic medium) with an average density of less than one atom per cubic meter. For comparison, the Milky Way has a diameter of at least 26,800 parsecs (87,400 ly) and is separated from the Andromeda Galaxy (with diameter of about 152,000 ly), its nearest large neighbor, by 780,000 parsecs (2.5 million ly.) Most of the galaxies are 1,000 to 100,000 parsecs in diameter (approximately 3,000 to 300,000 light years) and are separated by distances on the order of millions of parsecs (or megaparsecs). In 2021, data from NASA's New Horizons space probe was used to revise the previous estimate to roughly 200 billion galaxies ( 2 ×10 11), which followed a 2016 estimate that there were two trillion ( 2 ×10 12) or more galaxies in the observable universe, overall, and as many as an estimated 1 ×10 24 stars (more stars than all the grains of sand on all beaches of the planet Earth). It has a comoving distance of 32 billion light-years from Earth, and is seen as it existed just 400 million years after the Big Bang. As of March 2016, GN-z11 is the oldest and most distant galaxy observed. The Milky Way's central black hole, known as Sagittarius A*, has a mass four million times greater than the Sun. Many are thought to have supermassive black holes at their centers. Galaxies are categorized according to their visual morphology as elliptical, spiral, or irregular. Galaxies, averaging an estimated 100 million stars, range in size from dwarfs with less than a hundred million (10 8) stars, to the largest galaxies known - supergiants with one hundred trillion (10 14) stars, each orbiting its galaxy's center of mass. The word is derived from the Greek galaxias ( γαλαξίας), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 55,000 light-years in diameter and approximately 60 million light-years from Earth.Ī galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter.
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