Sh2-188, often called the Dolphin Nebula, is a planetary nebula in Cassiopeia about 850 light-years away. Its distinct crescent shape comes from a bow shock as the nebula plows through the interstellar medium at high speed. The leading edge glows with bright hydrogen-alpha and oxygen-III emission, while fainter filaments trail behind, outlining its extended structure.

This deep image combines Ha, OIII, and SII data for over 20 hours of total exposure, revealing delicate filaments and subtle color contrasts across the nebula. The mix of short and long exposures preserves both the bright rim and the faint outer shell, capturing the nebula’s interaction with surrounding space in remarkable detail.