The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Galaxia Kuklos; or simply "the Galaxy") is a barred spiral galaxy in the Local Group, and has special significance to humanity as the location of the solar system, which is located near the Orion Arm of the galaxy. Latin is the language originally spoken in the region around Rome called Latium. ... Wikipedia does not yet have an article with this exact name. ... This article is about a celestial body. ... Map of the local group The Local Group is the group of galaxies that includes our galaxy, the Milky Way. ... Binomial name Homo sapiens Linnaeus, 1758 Subspecies Homo sapiens idaltu (extinct) Homo sapiens sapiens Human beings define themselves in biological, social, and spiritual terms. ... Presentation of the solar system (not to scale). ... Observed structure of the Milky Ways spiral arms The Orion Arm or Local Arm (labeled 0) is a minor, spiral arm of the Milky Way galaxy. ...

The term "milky" originates from the hazy band of white light appearing across the celestial sphere visible from Earth, which comprises stars and other material lying within the galactic plane. The galaxy appears brightest in the direction of Sagittarius, towards the galactic center. White is a color (more accurately it contains all the colors of the visible spectrum and is sometimes described as an achromatic color—black is the absence of color) that has high brightness but zero hue. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye or, in a technical or scientific setting, electromagnetic radiation of any wavelength. ... In astronomy and navigation, the celestial sphere is an imaginary rotating sphere of gigantic radius, concentric with the Earth. ... Earth, also known as the Earth, Terra, and (mostly in the 19th century) Tellus, is the third planet outward from the Sun. ... The Pleiades star cluster A star is any massive gaseous body in outer space. ... Many galaxies, including the Milky Way in which our Sun and Earth are located, are disk-shaped: the majority of their visible mass (excluding possible dark matter) lies very close to a plane. ... Sagittarius (♐, and Latin for Archer) is a constellation of the zodiac, commonly depicted as a centaur drawing a bow. ... The Galactic Center is the rotational center of the Milky Way galaxy. ...

Relative to the celestial equator, the Milky Way passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux, indicating the high inclination of Earth's equatorial plane and the plane of the ecliptic relative to the galactic plane. The fact that the Milky Way divides the night sky into two roughly equal hemispheres indicates that the solar system lies close to the galactic plane. The celestial equator is a great circle on the imaginary celestial sphere, which could be constructed by inflating the Earths equator until it intersects with said sphere. ... Orion is a remarkable constellation, visible from most places on the globe (but not always the whole year long). ... Cassiopeia is a northern constellation which greek mythology considered to represent a vain queen. ... Crux, being Latin for cross, commonly known as the Southern Cross (in contrast to the Northern Cross), is the smallest of the 88 modern constellations, but also one of the most famous. ... The equator is an imaginary line drawn around a planet at a distance halfway between the poles. ... The plane of the Ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ... The term hemisphere is used in three different meanings: one-half of the Earth (or other planetary or stellar body; see also New World and Old World) Eastern Hemisphere and Western Hemisphere. ...

As a guide to the relative physical scale of the Milky Way, even if the galaxy were only 130 km (80 mi) in diameter, the solar system would be a mere 2 mm (0.08 in) in diameter. Also, a beam of light transmitted around the circumference of the Milky Way would take nearly 250,000 years to complete one revolution. The concept of scale is applicable if a system is represented proportionally by another system. ...

Age

The Galaxy is currently estimated to be about 13.6 billion (10⁹) years old, which is nearly as old as the Universe itself. The word billion, and its equivalents in other languages, refer to one of two different numbers. ... A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... The age of the Universe is defined as the largest possible value of proper time integrated along a timelike curve from the Earth at the present epoch back to the Big Bang. ...

This estimate is based upon research performed in 2004 by a team of astronomers: Luca Pasquini, Piercarlo Bonifacio, Sofia Randich, Daniele Galli, and Raffaele G. Gratton. They used the UV-Visual Echelle Spectrograph of the Very Large Telescope to measure, for the first time, the beryllium content of two stars in globular cluster NGC 6397. This allowed them to deduce the time elapsed between the rise of the first generation of stars in the entire Galaxy and the first generation of stars in the cluster, at 200 million to 300 million years. They added in the estimated age of the stars in the globular cluster: 13.4 ± 0.8 billion years. The sum is their estimated age of the Milky Way Galaxy: 13.6 ± 0.8 billion years. 2004 is a leap year starting on Thursday of the Gregorian calendar. ... One of the four telescopes that make up the VLT, named Kueyen. ... In classical physics and engineering, measurement is the the result of comparing physical quantities of objects, relations (e. ... General Name, Symbol, Number beryllium, Be, 4 Chemical series alkaline earth metals Group, Period, Block 2, 2, s Appearance white-gray metallic Atomic mass 9. ... The Pleiades star cluster A star is any massive gaseous body in outer space. ... A globular cluster is a spherical bundle of stars (star cluster) that orbits a galaxy as a satellite. ... Globular Cluster NGC 6397 (also known as NGC 6397) is a globular cluster in the Ara constellation. ... A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ...

Structure

Observed structure of the Milky Way's spiral arms

As of 2005, the Milky Way is thought to comprise a large barred spiral galaxy of Hubble type SBbc (loosely wound barred spiral) with a total mass of about 10¹² solar masses (M_☉), comprising 200-400 billion stars [1]. Observed spiral structure of the Milky Way galaxy following Taylor, J.H. & Cordes, J.M. ApJ 411, 674 (1993). ... Observed spiral structure of the Milky Way galaxy following Taylor, J.H. & Cordes, J.M. ApJ 411, 674 (1993). ... 2005 is a common year starting on Saturday of the Gregorian calendar. ... Wikipedia does not yet have an article with this exact name. ... The Hubble sequence is a classification of galaxy types developed by Edwin Hubble in 1936. ... Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... The word billion, and its equivalents in other languages, refer to one of two different numbers. ...

It was only in the 1980s that astronomers began to suspect that the Milky Way is a barred spiral rather than an ordinary spiral, which observations in 2005 with the Spitzer Space Telescope have since confirmed, showing that the galaxy's central bar is larger than previously suspected [2]. A spiral galaxy is a type of galaxy in the Hubble sequence which is characterized by the following physical properties: Spiral Galaxy M74 presents a face-on view of its spiral arms. ... 2005 is a common year starting on Saturday of the Gregorian calendar and is the current year. ... The Spitzer Space Telescope (SST) (formerly the Space Infrared Telescope Facility (SIRTF)) is an infrared space observatory, the fourth and final of NASAs Great Observatories. ...

The galactic disk has an estimated diameter of about 100,000 light-years (see 1 E20 m for a list of comparable distances). The distance from the Sun to the galactic center is estimated at about 27,700 light-years. The disk bulges outward at the center. A light year, abbreviated ly, is the distance light travels in one year: roughly 9. ... To help compare distances at different orders of magnitude this page lists lengths from 11,000 light years and 110,000 light years (1020 m and 1021 m). ... By ancient tradition, the Sun is the light in the heavens whose presence is day and whose absence is night. ...

As with most galaxies, it is suspected that the galactic center harbours a supermassive black hole, with Sagittarius A* being thought to be the most plausible candidate for the location of this extreme concentration of mass. Top: artists conception of a supermassive black hole drawing material from a nearby star. ... Sagittarius A* (pronounced A-star) is a bright and very compact source of radio emission at the centre of the Milky Way Galaxy, part of a larger astronomical feature at that location (Sagittarius A). ...

As is typical for many galaxies, the distribution of mass in the Milky Way is such that the orbital speed of most stars in the galaxy does not depend strongly on its distance from the center. Away from the central bulge or outer rim, the typical stellar velocity is 210 and 240 km/s [3]. Hence the orbital period of the typical star is directly proportional only to the length of the path travelled. This is unlike in the solar system where different orbits are also expected to have significantly different velocities associated with them. Presentation of the solar system (not to scale). ...

The galaxy's bar is thought to be about 27,000 light years long, running through the center of the galaxy at a 44±10 degree angle to the line between our sun and the center of the galaxy. It is composed primarily of red stars, believed to be ancient.

Observed and extrapolated structure of the spiral arms

Each spiral arm describes a logarithmic spiral (as do the arms of all spiral galaxies) with a pitch of approximately 12 degrees (see Valle, below). There are believed to be four major spiral arms which all start at the Galaxy's center. These are named as follows, according to the image at right: This is a diagram of the arms of the Milky Way Galaxy based on both observed information and extrapolations where current techology cannot penetrate. ... This is a diagram of the arms of the Milky Way Galaxy based on both observed information and extrapolations where current techology cannot penetrate. ... Logarithmic spiral (pitch 10°) Cutaway of a nautilus shell showing the chambers arranged in an approximately logarithmic spiral A logarithmic spiral, equiangular spiral or growth spiral is a special kind of spiral curve which often appears in nature. ...

• 2 and 8 - 3kpc and Perseus Arm
• 3 and 7 - Norma and Cygnus Arm (Along with a newly discovered extension - 6)
• 4 and 10 - Crux and Scutum Arm
• 5 and 9 - Carina and Sagittarius Arm

There are at least two smaller arms or spurs, including: The parsec (symbol pc) is a unit of length used in astronomy. ... The Perseus Arm (labeled +I) is a spiral arm of the Milky Way galaxy with a radius of 10. ... The Norma Arm or 3-kpc Arm is an inner spiral arm at the center of the Milky Way galaxy. ... Observed structure of the Milky Ways spiral arms The Cygnus Arm or Outer Arm (labeled +II) is one of four major spiral arms in the Milky Way galaxy, along with the Sagittarius Arm. ... The Scutum-Crux Arm or Centaurus Arm is a spiral arm of the Milky Way galaxy. ... The Scutum-Crux Arm or Centaurus Arm is a spiral arm of the Milky Way galaxy. ... The Sagittarius Arm or Sagittarius-Carina Arm (labeled -I) is one of two major spiral arms of the Milky Way galaxy, along with the Cygnus Arm. ... The Sagittarius Arm or Sagittarius-Carina Arm (labeled -I) is one of two major spiral arms of the Milky Way galaxy, along with the Cygnus Arm. ...

• 11 - Orion Arm (which contains the solar system and the Sun - 12)

Outside of the major spiral arms is the Outer Ring or Monoceros Ring, a ring of stars around the Milky Way proposed by astronomers Brian Yanny and Heidi Jo Newberg, which consists of gas and stars torn from other galaxies billions of years ago. Observed structure of the Milky Ways spiral arms The Orion Arm or Local Arm (labeled 0) is a minor, spiral arm of the Milky Way galaxy. ... By ancient tradition, the Sun is the light in the heavens whose presence is day and whose absence is night. ... Monoceros Ring is a proposed ring of stars around the Milky Way which consists of stars torn from other galaxies as they merged with the Milky Way galaxy over the course of billions of years. ...

The galactic disk is surrounded by a spheroid halo of old stars and globular clusters. While the disk contains gas and dust obscuring the view in some wavelengths, the halo does not. Active star formation takes place in the disk (especially in the spiral arms, which represent areas of high density), but not in the halo. Open clusters also occur primarily in the disk. A spheroid is a quadric surface in three dimensions obtained by rotating an ellipse about one of its principal axes. ... The galactic halo is a region of space surrounding spiral galaxies, including our galaxy, the Milky Way. ... A globular cluster is a spherical bundle of stars (star cluster) that orbits a galaxy as a satellite. ... The Pleiades star cluster A star is any massive gaseous body in outer space. ... An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud, and are still gravitationally bound to each other. ...

X-ray image of Milky Way taken by Chandra X-ray Observatory

x-ray image of milky way, from NASA - public domain File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. ...

The Sun's place in the Milky Way

The Sun (and therefore the Earth and Solar System) may be found close to the inner rim of the Orion Arm, in the Local Fluff, 8.5±0.5 kpc from the galactic center. The distance between the local arm and the next arm out, the Perseus Arm, is about 6,500 light-years (see [4]). Earth, also known as the Earth, Terra, and (mostly in the 19th century) Tellus, is the third planet outward from the Sun. ... Presentation of the solar system (not to scale). ... The Local Fluff is a relatively dense cloud of interstellar gas which formed where the Local Bubble and the Loop I Bubble met. ... The Galactic Center is the rotational center of the Milky Way galaxy. ... To help compare different orders of magnitude, this page lists distances between 1019 m (1,100 light years) and 1020 m (11,000 light years). ...

The Apex of the Sun's Way, or the solar apex, refers to the direction that the Sun travels through space in the Milky Way. The general direction of the sun's galactic motion is towards the star Vega near the constellation of Hercules, at an angle of roughly 86 degrees to the direction of the galactic center. The sun's orbit around the galaxy is expected to be roughly elliptical with the addition of perturbations due to the galactic spiral arms and non-uniform mass distributions. We are presently about 8.5 kpc from the center of the galaxy and roughly 1/8 of an orbit before perigalacton (the sun's closest approach to the center, ~8.3 kpc). The Apex of the Suns Way, or the solar apex, refers to the direction that the Sun travels through space. ... Hercules and Cacus, by Baccio Bandinelli, 1525 - 1534. ... The parsec (symbol pc) is a unit of length used in astronomy. ...

It would take the solar system about 200-250 million years to complete one orbit ("galactic year"), and so is thought to have completed about 20-25 orbits during its lifetime. The orbital speed is 217 km/s, i.e. 1 light-year in ca. 1400 years, and 1 AU in 8 days. Presentation of the solar system (not to scale). ... The orbital speed of a body, generally a planet, a natural satellite, an artificial satellite, or a multiple star, is the speed at which it orbits around the barycenter of a system, usually around a more massive body. ... The astronomical unit (AU or au or a. ...

The galactic neighborhood

The Milky Way, the Andromeda Galaxy and the Triangulum Galaxy are the major members of the Local Group, a group of some 35 closely bound galaxies; The Local Group is part of the Virgo Supercluster. This image is a Galaxy Evolution Explorer observation of the large galaxy in Andromeda, Messier 31. ... Messier Object 33, the Triangulum Galaxy. ... Map of the local group The Local Group is the group of galaxies that includes our galaxy, the Milky Way. ... The Virgo Supercluster or Local Supercluster is the supercluster of galaxies that contains the Local Group and with it our galaxy, the Milky Way. ...

The Milky Way is orbited by a number of dwarf galaxies in the Local Group. The largest of these is the Large Magellanic Cloud with a diameter of 20,000 light years. The smallest, Carina Dwarf, Draco Dwarf, and Leo II are only 500 light years in diameter. The other dwarfs orbiting our galaxy are the Small Magellanic Cloud; Canis Major Dwarf, the closest; Sagittarius Dwarf Elliptical Galaxy, previously thought to be the closest; Ursa Minor Dwarf; Sculptor Dwarf, Sextans Dwarf, Fornax Dwarf, and Leo I. A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Ways 200-400 billion stars. ... The Large Magellanic Cloud (also known as LMC) is a dwarf galaxy that is in orbit around our own Milky Way galaxy. ... The Small Magellanic Cloud (SMC) —also known as NGC 292— is an irregular galaxy, sometimes classified as a dwarf galaxy, in orbit around the Milky Way Galaxy. ... The Canis Major Dwarf Galaxy located in the same part of the sky as the constellation of Canis Major. ... The Sagittarius Dwarf Elliptical Galaxy (Sag DEG) is a satellite galaxy of the Milky Way Galaxy. ... for SDIG, see Sculptor Dwarf Irregular Galaxy The Sculptor Dwarf Galaxy (also called E351-G30, PGC 3589, A0058, Sculptor Dwarf Spheroidal Galaxy) is a dwarf spheroidal galaxy in the Local Group that is a satellite of the Milky Way in the direction of the constellation of Sculptor. ... The Leo I Dwarf Galaxy (or simply Leo I) is a dwarf spheroidal galaxy in the Local Group. ...

Mythology

Main article: Milky Way (mythology)

There are many creation myths around the world regarding the Milky Way. In particular, there are two similar ancient Greek stories that explain the etymology of the name Galaxias (Γαλαξίας) and its association with milk (γάλα). Some myths associate the constellation with a herd of cattle whose milk gives the sky its blue glow. In Eastern Asia, people believed that the hazy band of stars was the "Silvery River" of Heaven. There are numerous legends in many traditions around the world regarding the creation of the Milky Way. ... Creation beliefs and stories describe how the universe, the Earth, life, and/or humanity came into being. ... The Silvery River of Heaven is the great swath of white/silver nebulosity that is the plane of the disc of the Milky Way. ...

References

1. J. P. Vallée, "The Milky Way's Spiral Arms traced by Magnetic Fields, Dust, Gas and Stars", The Astrophysical Journal, volume 454, pp. 119-124, 1995. Available online through NASA's Astrophysics Data System
2. Press release, Canadian Galactic Plane Survey
3. Press release, European Southern Observatory
4. Sandage, A. & Fouts, G., The Astrophysical Journal, volume 97, p. 74, 1987
5. Foley, Ryan J. "Study Details Bar at Center of Milky Way". Retrieved August 17, 2005.

The Astrophysical Journal is one of the foremost research journals devoted to recent developments, discoveries, and theories in astronomy and astrophysics. ... The Astrophysical Journal is one of the foremost research journals devoted to recent developments, discoveries, and theories in astronomy and astrophysics. ...

External links

• The Milky Way Galaxy, SEDS Messier pages
• MultiWavelength Milky Way NASA site with images and VRML models
• An Atlas of the Universe
• Proposed Ring around the Milky Way

• Milky Way spiral gets an extra arm New Scientist.com
  • http://www.solstation.com/x-objects/gal2arc.jpg
• Possible New Milky Way Spiral Arm Sky and Telescope .com
  • http://skyandtelescope.com/mm_images/6829.jpg