Sunday, Mar 2, 2025

Sh2-173, also known as the Phantom of the Opera Nebula, is an H II region located in the constellation Cassiopeia, approximately 8,800 light-years from Earth. It is part of the Perseus Arm of the Milky Way and is characterized by an intricate structure shaped by stellar winds and radiation from massive stars. The nebula is ionized primarily by the OB-type stars of the open cluster Stock 18, which formed from the same molecular cloud. Its nickname comes from its resemblance to the iconic mask from The Phantom of the Opera. The nebula is a site of active star formation, with dust and gas interacting to create complex filaments and dark regions visible in infrared and optical wavelengths.