Sh2-155, Cave Nebula

This image was obtained with the wide-field view of the Mosaic camera on the Mayall 4-meter telescope at Kitt Peak National Observatory. Sh2-155, informally known as the "cave nebula," is dark cloud of gas embedded in a giant emission nebula. The top edge of the cloud is illuminated by several hot, massive (OB) stars that are part of the Cepheus OB3 assocation. The image was generated with observations in Hydrogen alpha (red), Sulphur [S II] (blue) and I (orange) filters. In this image, North is left, East is down.