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summer milky way

 

Covering more than 150 square degrees of sky, this image represents what I believe to be the very essence of our own Milky Way Galaxy. The northwest corner of the constellation Sagittarius is inarguably one of the richest starfields in the entire sky. It is all here--emission nebulae, dark nebulae, reflection nebulae, globular clusters, and open clusters--from the very bright to the extremely faint. The most obvious features, of course, are the Lagoon and Trifid Nebulae located near bottom and the densely packed stars of Messier 24 just above center. If you hold your mouse over the image above, a b&w image will appear with many of the more obvious features labeled for identification. The intense coloration of the denser areas is due to several factors. First of all, this image represents an area of our galaxy located less than 5 degrees from the galactic center. As previously mentioned in the Messier 31 and Messier 33 articles, the core areas or central "bulge" of spiral galaxies are typically composed of older G and K type stars which are yellow and orangish in color. Furthermore, we are actually peering through several different spiral arms when glancing towards the center of the Milky Way. This means that the light from many of the stars that we see in this direction has traveled through copius amounts of interstellar dust and gas before reaching us. When such dust particles are packed with enough density, they completely block the transmission of light in the visible part of the electromagnetic spectrum, thus creating a silhouette or "dark nebula". Such dimming of starlight by the interstellar medium is called interstellar extinction. However, when the dust is not so thick, it simply "reddens" the starlight by attenuating the shorter blue wavelengths of light and passing the longer red wavelengths. This results in the core area of our galaxy appearing quite ruddy to photographic instruments which typically have a high sensitivity towards the red end of the spectrum. The large quantity of interstellar dust and gas is made quite obvious by the many obscuring clouds forming the Great Rift, which appears as a darkened band running along the center of the visible Milky Way. In this depiction, the Great Rift can be seen traversing the entire frame from the upper left near Messier 17 down to the lower right of the image. Image taken with Canon 70-200mm USM-L lens at 135mm/f5.6 and STL-11000M. LRGB image composed of 90 minutes of L and 40 minutes each R,G,B. Be sure to click on the above image for the high resolution version.