Scope: Televue NP127is
Mount: Losmandy G11
Guide: TV Pronto + Lodestar
Data aquired from my back garden observatory in Macclesfield UK.
Sh2-157 is a faint nebulous region in Cassiopeia on the border with Cephus, it cannot be seen visually in amateur class instuments but the power of long exposures using a CCD camera is able to reveal its true nature. This image is a 10 hour narrow-band composite of Ha, OIII and SII wavelengths which shows the loop at the right-hand formed by strong stellar winds and the area is dominated by triple-ionised oxygen resulting in the blue colouration. The left-hand side is mostly ionised Hydrogen (HII) which shows as red/yellow areas in this image and is illuminated by powerful UV radiation from nearby bright O-type stars.