dust, and stars. They are arranged in a nearly spherical halo around the Milky Way, with relatively few toward the galactic plane but a heavy concentration toward the centre. The transverse (or tangential) velocity, T, is given by T V sin.74 / p where p is the stars parallax in arc seconds. These arms are contained in what is called the disk of the galaxy. Frequently it is even possible to observe the effects of several concentrations of interstellar gas between Earth and the background stars and thereby determine the kinematics of the gas in different parts of the Galaxy. If one were to assume that the galaxy is made up only of matter that we can see, then the rotation rate would be significantly less than what we observe. As such, dark matter is estimated to make up 90 percent of the mass of the galaxy. "It's almost like we're sailing through the galaxy sideways Merav Opher, an astrophysicist at George Mason University in Virginia, told.
The brightest open clusters are considerably fainter than the brightest globular clusters. Ages of open clusters are determined by comparing their stellar membership with theoretical models of stellar evolution. This gas was enriched in the heavy elements (i.e., elements heavier than helium) produced in stars during the later stages of their evolution, so that the interstellar gas in the Galaxy is continually being changed.
A conspicuous component of the tomorrow Is Another Country Galaxy is the collection of large, bright, diffuse gaseous objects generally called nebulae. The brightest of these cloudlike objects are the emission nebulae, large complexes of interstellar gas and stars in which the gas exists in an ionized and excited state (with the electrons of the atoms excited to a higher than normal energy level). The Galaxy contains more than 150 globular clusters (the exact number is uncertain because of obscuration by dust in the Milky Way band, which probably prevents some globular clusters from being seen). As time progresses after the formation of a cluster, the massive stars, which evolve the fastest, gradually disappear from the cluster, becoming white dwarf stars or other underluminous stellar remnants. The H II regions are concentrated in the spiral arms of the Galaxy, though some exist between the arms. About the Map, this map shows the full extent of the Milky Way galaxy - a spiral galaxy of at least two hundred billion stars. Spitzer can peer through the dust to give us extraordinarily clear views of what is going on at the heart of the galaxy and in star-forming regions. Minor components of the gas, such as sodium and calcium, absorb light at specific wavelengths, and they thus cause the appearance of absorption lines in the spectra of the stars that lie beyond the gas. In the case of the Virgo Supercluster, at least 100 galaxy groups and clusters are located within it massive 33 megaparsec (110 million light-year) diameter. More complete information on the dust in the Galaxy comes from infrared observations. It became possible in the 1990s to discover very young open clusters that previously had been entirely hidden in deep, dusty regions.
The Milky Way Galaxy