Galaxy Structure

A very large body of information has been collected on the structure of the Galaxy. Here we can only concentrate on a small selection of the most recent and most important observational facts and theoretical findings. The MILKY WAY GALAXY belongs to the Local Group, a smaller group of three large and over 30 small galaxies, and is the second largest (after the Andromeda Galaxy M31) but perhaps the most massive member of this group. The Milky Way is most likely a BARRED SPIRAL GALAXY of Hubble type SBc. We are situated within the outer regions of its spiral disk, only about 14 ly above the equatorial symmetry plane but about 8 kpc or 26 400 ly from the Galactic Center (1 pc ~ 3.29 ly ~ 3 × 9.5 × 10 km). The Milky Way forms a luminous band spanning all around the sky. This symmetry plane is also called the ‘Galactic Equator’. In addition to the luminous stars there is also a dark band due to the obscuration of stellar light via gas and dust within the GALACTIC PLANE. The center of the Galaxy lies in the direction of the constellation Sagittarius, close to the border of both neighbor constellations Scorpius and Ophiuchus. The coordinates of the center (Rogers et al 1994) are α(2000) = 17 45 40.045±0.010 and δ(2000) = −29o 00' 27.9"±0.2".