The milky way galaxy
In our galaxy we have over 100 billion in the system. We are in one of the sprial arms of this galaxy. A spiral galaxy like the milky way has basic components to its visible matter:(1) the disk ( containting the spiral arms), (2) the halo, and (3) the nucleus or central bluge. In addition to these visible components, the galaxy contains at least three other components that are"invisible": the galactic magnetic feild, charged particles trapped in the galactic magnetic feild, and a halo of" darn and gas is dark matter" that is of unkown composition but that makes itself felt by its gravitational influence on the visible matter. most of the gas and dust of the mliky way is contained int he disk. This material between the stares is often termed the interstellar medium. The primary hydrogen and helium, and the dust makes many regions of the disk opaque. For example, we cannot see the center of the galaxy in visible light because of intervening dust clouds in the disk. The adjiacent image shows the nearby andromeda galaxy, which also has the messier designation M31. it is a spiral galaxy much like our own, and dark dust lanes between the spiral arms are quite in this image REF. The disk is quite prominent in our own galaxy and in other spiral because of its spiral arms, which contain many hot young stars and therefore is luminous. These ypunger stars are often contianed in assocations, which are groups of typically 10-100 young stars ths at are moving together through space because they have been recently fromed from from the same nebula, and open clusters, which contain 100-1000 star and are more strongly bound together gravitationally than assciation.

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The halo of the galaxy
The halo is a spherical cloud of thinly scattered stars and globular clusters. It is the largest component of the Galaxy, extending to radii of about 40,000 - 50,000 parsecs. The disk and bulge components are located in the center of the halo.
The disk component includes all of the material (gas, dust, stars, and star clusters) which are confined to the plane of rotation of the galaxy. The diameter of the disk is about 30,000 parsecs. It has a thickness of about 600 parsecs for the cold components (like neutral gas) and about 2000 parsecs for the hot components (like ionized gas). (The difference arises because the cold components have less energy and therefore don't move as far or as fast as the hot components.) The Sun is located at about 8,500 parsecs from the center, roughly in the middle of the disk
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The disk of the galaxy
The disk includes the
spiral arms, which are long patterns of bright stars, star clusters, gas, and dust in the shape of arms. It also conatins two kinds of star clusters: open clusters, and associations.
Open clusters are collections of stars which are held together by their own gravity. They are not as dense as Globular clusters; they typically contain about 100 - 1000 stars in a region approximately 3-30 parsecs in diameter. They survive about a few billion years and are concentrated along the band of the Milky Way. A well known example of an open cluster is the Pleaides, shown below.
An infrared
COBE* photo of our own Milky Way galaxy seen edge-on from within. The Milky Way is 100,000 light years wide, 10,000 light years thick in the central bulge, and 3000 light years thick in the spiral arms (a light year is six trillion miles). *COBE is an acronym for The Cosmic Background Explorer satellite, developed by NASA’s Goddard Space Flight Center to measure the diffuse infrared and background microwave radiation from the early Universe after the Big Bang.
This Milky Way Galaxy 200 billion stars page and the entire website are excerpted from
//You and the Universe//, a handmade, individualized fine art book on astrology, mythology and astronomy through which the recipient's complete astrological reading is woven.
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Milky way galaxy
Our Sun is a star 864,000 miles in diameter, composed of 75% hydrogen and 25% helium, the two lightest elements in the universe. It contains 99.8% of all of the mass in the solar system—the planets and everything else amount to only 1/500th of the total. The surface of the Sun is 5,800° on the absolute Kelvin scale (or 9600° Fahrenheit), but in the corona—which extends out for millions of miles, is ten billion times less dense than the atmosphere of the Earth at sea level, and is only visible during eclipses—the temperature averages over one million degrees Kelvin (2 million Fahrenheit). In fact in some places the corona can reach 3 million degrees Kelvin (5 million Fahrenheit)! Since temperatures ordinarily fall as one moves away from the source of the heat, the source of the corona's relatively high temperature remains an unsolved puzzle. At the Sun’s core the temperature is 15.6 million degrees, the pressure is 250 billion times the pressure at sea level on Earth, and the density of this lightest of all gases is more than 150 times that of water. To read more about our Sun, the star called Sol,
click here.All of us on the planet earth live in the milky way galaxy and if your at a space station. On a dark night we may see a band of light stretching across the sky. With binoculars or a small telescope this band is partially resloved into stars, as illustrated in the image on the right img source. We call this band the milky way; it is composed primarily of stars light as a faint glow. The milky way is anexample of a gigantic collection of stars, gas, and dust that we call a galaxy.