The sky around Sh2-203 at true scale, north up and east left, with stars to magnitude 8. The circles show the field of a low-power eyepiece and of 10×50 binoculars.
Sh2-203 is an emission nebula (H II region) in Perseus, 7,800 light-years away
Sh2-203 (LBN 685) is an emission nebula (H II region) in the constellation Perseus, 7,800 light-years away. It is a telescope object, 6 inches or larger, and it is highest in the evening sky in December.
Nebula: a cloud of gas and dust. Emission nebulae glow on their own, lit by ultraviolet light from hot young stars; reflection nebulae shine by starlight scattered from dust; dark nebulae block the light behind them.
Sh2-203 is Sh2-203 in the Sharpless catalog
Stewart Sharpless listed it in his catalog of H II regions (1959), drawn from the red and blue prints of the Palomar Sky Survey. He rated each region's brightness on a scale of 1 to 3; Sh2-203 is faint (class 1 of 3). It is also listed as LBN 685.
Finding Sh2-203 from Mirfak
Sh2-203 lies 5.0° north of Mirfak, the magnitude 1.8 star. Three fingers held at arm's length cover about 5°.
Sh2-203 is highest in the evening in December
The chart gives its height above the horizon at 9 pm through the year, from 60°N to 40°S. It can be seen from the whole northern hemisphere and south to about 35°S, and never sets north of 35°N.
Sh2-203 is 7,800 light-years away
The light seen from Sh2-203 tonight left it about 7,800 years ago. It ranks 83 of 159 by distance among the Sharpless nebulae with a measured distance. Distance source: Gaia EDR3 ionizing stars, Mendez-Delgado et al. 2022 (2.39 kpc).
