The sky around vdB 138 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.
vdB 138 is a reflection nebula in Cygnus, 1,960 light-years away
vdB 138 (LBN 403, DG 166) is a reflection nebula in the constellation Cygnus, 1,960 light-years away. spans 15′ of sky, about 8.4 light-years across. It is a telescope object, 6 inches or larger, and it is highest in the evening sky in September.
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.
vdB 138 is vdB 138 in the Van den Bergh catalog of reflection nebulae
Sidney van den Bergh listed it in his catalog of reflection nebulae (1966), drawn from the Palomar Sky Survey. He chose nebulae lit by a star bright enough to appear in the Bonner and Cordoba star catalogs. The star that lights it is HD 199714, B8Ib, magnitude 8.3. He rated it faint in brightness and blue in color.
Finding vdB 138 from Deneb
vdB 138 lies 4.1° northeast of Deneb, the magnitude 1.2 star. Three fingers held at arm's length cover about 5°.
vdB 138 is highest in the evening in September
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 42°S, and never sets north of 42°N.
vdB 138 is 1,960 light-years away
The light seen from vdB 138 tonight left it about 1,960 years ago, around 66 AD. It ranks 87 of 158 by distance among the Van den Bergh nebulae. Distance source: Gaia DR3 parallax of the illuminating star via AT-HYG v3.2 (602 pc).
