The sky around Sh2-255 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.
Sh2-255 is an emission nebula (H II region) in Orion, 6,390 light-years away
Sh2-255 (IC 2162, LBN 859) is an emission nebula (H II region) in the constellation Orion, 6,390 light-years away. It is a telescope object, 6 inches or larger, and it is highest in the evening sky in February.
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.
Sh2-255 is Sh2-255 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; Sh2-255 is bright (class 3 of 3). It is also listed as LBN 859.
Finding Sh2-255 from Alhena
Sh2-255 lies 6.1° west of Alhena, the magnitude 1.9 star. Three fingers held at arm's length cover about 5°.
Sh2-255 is highest in the evening in February
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 72°S, and never sets north of 72°N.
Sh2-255 is 6,390 light-years away
The light seen from Sh2-255 tonight left it about 6,390 years ago. It ranks 59 of 159 by distance among the Sharpless nebulae with a measured distance. Distance source: Gaia EDR3 ionizing stars, Mendez-Delgado et al. 2022 (1.96 kpc).
