please wirte an essay on STARS AND GALAXY in 1500 words
Answers
Answer:
A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems, all held together by gravity. We live on a planet called Earth that is part of our solar system. ... A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems. A galaxy is held together by gravity.
Answer:
A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter.[1][2] The word galaxy is derived from the Greek galaxias (γαλαξίας), literally "milky", a reference to the Milky Way. Galaxies range in size from dwarfs with just a few hundred million (108) stars to giants with one hundred trillion (1014) stars,[3] each orbiting its galaxy's center of mass.
Galaxies are categorized according to their visual morphology as elliptical,[4] spiral, or irregular.[5] Many galaxies are thought to have supermassive black holes at their centers. The Milky Way's central black hole, known as Sagittarius A*, has a mass four million times greater than the Sun.[6] As of March 2016, GN-z11 is the oldest and most distant observed galaxy with a comoving distance of 32 billion light-years from Earth, and observed as it existed just 400 million years after the Big Bang.
Research released in 2016 revised the number of galaxies in the observable universe from a previous estimate of 200 billion (2×1011)[7] to a suggested two trillion (2×1012) or more[8][9] and, overall, as many as an estimated 1×1024 stars[10][11] (more stars than all the grains of sand on planet Earth).[12] Most of the galaxies are 1,000 to 100,000 parsecs in diameter (approximately 3,000 to 300,000 light years) and separated by distances on the order of millions of parsecs (or megaparsecs). For comparison, the Milky Way has a diameter of at least 30,000 parsecs (100,000 ly) and is separated from the Andromeda Galaxy, its nearest large neighbor, by 780,000 parsecs (2.5 million ly.)
The space between galaxies is filled with a tenuous gas (the intergalactic medium) having an average density of less than one atom per cubic meter. The majority of galaxies are gravitationally organized into groups, clusters, and superclusters. The Milky Way is part of the Local Group, which is dominated by it and the Andromeda Galaxy and is part of the Virgo Supercluster. At the largest scale, these associations are generally arranged into sheets and filaments surrounded by immense voids.[13] Both the Local Group and the Virgo Supercluster are contained in a much larger cosmic structure named Laniakea.[14]
Explanation:
The word galaxy was borrowed via French and Medieval Latin from the Greek term for the Milky Way, galaxías (kúklos) γαλαξίας (κύκλος)[15][16] 'milky (circle)', named after its appearance as a milky band of light in the sky. 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. 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 faint band of light known as the Milky Way.[17][18]
In the astronomical literature, the capitalized word "Galaxy" is often used to refer to our galaxy, the Milky Way, to distinguish it from the other galaxies in our universe. The English term Milky Way can be traced back to a story by Chaucer c. 1380:
" identification of the Andromeda Galaxy, describing it as a "small cloud".[36] In 964, Al-Sufi probably mentioned the Large Magellanic Cloud in his Book of Fixed Stars (referring to "Al Bakr of the southern Arabs",[37] since at a declination of about 70° south it was not visible where he lived); it was not well known to Europeans until Magellan's voyage in the 16th century.[38][37] The Andromeda Galaxy was later independently noted by Simon Marius in 1612.[36] In 1734, philosopher Emanuel Swedenborg in his Principia speculated that there may be galaxies outside our own that are formed into galactic clusters that are minuscule parts of the universe which extends far beyond what we can see. These views "are remarkably close to the present-day views of the cosmos."[39] In 1745, Pierre Louis Maupertuis conjectured that some nebula-like objects are collections of stars with unique properties, including a glow exceeding the light its stars produce on their own, and repeated Johannes Hevelius's view that the bright spots are massive and flattened due to their rotation.[40] In 1750, Thomas Wright speculated (correctly) that the Milky Way is a flattened disk of stars, and that some of the nebulae visible in the night sky might be separate Milky Ways.[31][41]
Photograph of the "Great Andromeda Nebula" by Isaac Roberts, 1899, later identified as the Andromeda Galaxy
Toward the end of the 18th century, Charles Messier compiled a catalog containing the 109 brightest celestial objects having nebulous appearance. Subsequently, William Herschel assembled a catalog of 5,000 nebulae.[31] In 1845, Lord Rosse constructed a new telescope and was able to distinguish between elliptical and spiral nebulae. He also managed to make out individual point sources in some of these nebulae, lending credence to Kant's earlier conjecture.[42]
.