Home sweet home I
Our galaxy, the Milky Way, is shaped like a large, thin disk with a central bulge. If viewed from above, it would appear as a large barred spiral. Most visible objects are located within this disk, which is remarkably thin compared to other galaxies, and it is surrounded by a weak halo containing stars and globular clusters.
Our solar system is located far outside the central region of the disk and near its central plane. The glowing band of the Milky Way that we see in the night sky is the projection of this disk. It consists of millions of distant stars and other objects. Most visible stars, nebulae, and star clusters above or below the band are objects relatively close to the Sun. The brightest and most spectacular regions of the Milky Way indicate the direction toward the center of the galaxy, located in the constellations Carina, Norma, Scorpius, Sagittarius, and Scutum.
The Milky Way is primarily formed by stars, cold and invisible molecular clouds, and mysterious dark matter. Gravitational forces acting between these objects cause them to rotate around the center of the galaxy. The overall structure of our galaxy is a result of these forces combined with ongoing star formation processes: new stars are born in the dense regions of interstellar matter. The most massive stars ionize hydrogen in their vicinity, forming reddish glowing nebulae. At the end of their short lifetime, they explode as supernovae, mixing up gas and dust clouds and enriching their surroundings with heavy elements like metals. Shock waves from these explosions may stimulate new star formation. Dust particles are created in the cool outer regions of red giant stars. Dust clouds have a significant impact on the visible appearance of the Milky Way, as they absorb visible light very efficiently. Most of the objects that we can see in the arms of the Milky Way are only a few thousand light-years apart, whereas the galactic center is invisible to our eyes.
The image covers a field of about 65x45° in the sky. Most deep-sky objects are in the neighborhood of our Sun, just 4,000 – 7,000 light-years away. Some "holes" in the dust clouds allow us to have a deeper view into the galaxy: the Sagittarius cloud M24 is part of the second-nearest spiral arm, the Norma arm, which is 12,000 – 16,000 light-years away. The globular cluster NGC 6522 shines through the so-called Baade window, located beyond the galactic center.
Starting from the impressive star clusters M6 and M7, the bright HII regions M8, M20, M17, M16, and NGC 6604 form a chain in the northern direction. Additionally, many open clusters are visible in the band of the Milky Way, whereas some globular clusters outside the band are located in the halo of the galaxy. The striking and colorful Antares region is quite near to us – here, the giant star Antares ionizes surrounding gas clouds and produces dust particles.
