The sky around vdB 91 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 91 is a reflection nebula in Monoceros, 3,790 light-years away
vdB 91 is a reflection nebula in the constellation Monoceros, 3,790 light-years away. spans 1.8′ of sky, about 2.0 light-years across. 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.
vdB 91 is vdB 91 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 BD-10 1839, B3V, magnitude 9.7. He rated it faint in brightness and blue in color.
Finding vdB 91 from Sirius
vdB 91 lies 7.5° northeast of Sirius, the magnitude -1.4 star. Three fingers held at arm's length cover about 5°.
vdB 91 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 southern hemisphere and north to about 79°N, and never sets south of 79°S.
vdB 91 is 3,790 light-years away
The light seen from vdB 91 tonight left it about 3,790 years ago. It ranks 134 of 158 by distance among the Van den Bergh nebulae. Distance source: Gaia DR3 parallax of the illuminating star via AT-HYG v3.2 (1161 pc).
