The panoramic optical view of the Milky Way Galaxy was obtained using a Minolta 28mm lens. The central buldge of the Milky Way Galaxy is seen prominently. The dark patches in the image are due to intervening dust and gas clouds that absorb the optical radiation. These same clouds of gas and dust radiate in radio wavelengths as seen in the accompanying radio image.
A large portion of interstellar gas in a spiral galaxy is molecular hydrogen and much is contained in a part of the galaxy called the giant molecular cloud. Carbon monoxide molecule (CO) is an excellent tracer of the distribution of molecular hydrogen molecules in the Galaxy. Carbon monoxide has been used to show that most star formation occurs in dense molecular clouds. Giant molecular clouds form primarily in the arms of spiral galaxies. This radio image of the plane of our Galaxy was obtained with a 1.2 meter radio telescope. The same clouds of CO gas radiating in radio wavelength obscure the optical radiation from the background starlight and coincide with dark patches seen in the accompanying optical image.