The sky around Sh2-198 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.
Sh2-198 is an emission nebula (H II region) in Cassiopeia, 8,120 light-years away
Sh2-198 (LBN 669) is an emission nebula (H II region) in the constellation Cassiopeia, 8,120 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.
Sh2-198 is Sh2-198 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; Sh2-198 is medium (class 2 of 3). It is also listed as LBN 669.
Finding Sh2-198 from γ Per
Sh2-198 lies 6.5° north of γ Per, the magnitude 2.9 star. Three fingers held at arm's length cover about 5°.
Sh2-198 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 30°S, and never sets north of 30°N.
Sh2-198 is 8,120 light-years away
The light seen from Sh2-198 tonight left it about 8,120 years ago. It ranks 86 of 159 by distance among the Sharpless nebulae with a measured distance. Distance source: spectrophotometric, Foster & Brunt 2015 (2.49 kpc).
