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Learn about galaxies, the large collections of stars, planets, and gas and dust that form the universe. Find out about the types, shapes, ages, and features of galaxies, and how they are organized into groups, clusters, and superclusters.
- Evolution
Each galaxy deforms in reaction to the gravitational pull of...
- Large Scale Structures
Galaxies, galaxy groups and clusters, superclusters, and...
- Evolution
Learn the meaning of galactic, an adjective that describes something related to a galaxy or very large. See synonyms, examples, word history, and related entries of galactic.
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. [1] [2] The word is derived from the Greek galaxias ( γαλαξίας ), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System.
- Overview
- Early observations and conceptions
A galaxy is any of the systems of stars and interstellar matter that make up the universe. Many such assemblages are so enormous that they contain hundreds of billions of stars. Galaxies usually exist in clusters, some of which measure hundreds of millions of light-years across.
Are all galaxies the same shape?
Galaxies differ in shape, with variations resulting from how the systems were formed and subsequently evolved. Galaxies are extremely varied not only in structure but also in the amount of activity observed.
What are the types of galaxies?
Galaxy classification is based on the scheme proposed by the American astronomer Edwin Hubble. Hubble’s scheme is based on the optical appearance of galaxy images and divided into three general classes: ellipticals, spirals, and irregulars.
What is an example of a Sa galaxy?
The dispute over the nature of what were once termed spiral nebulae stands as one of the most significant in the development of astronomy. On this dispute hinged the question of the magnitude of the universe: were we confined to a single, limited stellar system that lay embedded alone in empty space, or was our Milky Way Galaxy just one of millions of galaxies that pervaded space, stretching beyond the vast distances probed by our most powerful telescopes? How this question arose, and how it was resolved, is an important element in the development of our prevailing view of the universe.
Up until 1925, spiral nebulae and their related forms had uncertain status. Some scientists, notably Heber D. Curtis of the United States and Knut Lundmark of Sweden, argued that they might be remote aggregates of stars similar in size to the Milky Way Galaxy. Centuries earlier the German philosopher Immanuel Kant, among others, had suggested much the same idea, but that was long before the tools were available to actually measure distances and thus prove it. During the early 1920s astronomers were divided. Although some deduced that spiral nebulae were actually extragalactic star systems, there was evidence that convinced many that such nebulae were local clouds of material, possibly new solar systems in the process of forming.
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Apr 17, 2019 · Learn about the types, origins, and features of galaxies, the sprawling systems of stars and dark matter held together by gravity. Find out how galaxies evolve, interact, and merge over time.
Learn how galaxies form, grow, and change over time, from the earliest stages of the universe to the present day. Explore images and facts about spiral, barred, colliding, merging, and ring galaxies, and their black holes.
Learn how galaxies, galaxy groups, clusters, superclusters, and the intergalactic medium form the cosmic web of the universe. Explore images and visualizations of these structures and their properties.
