The sky around vdB 123 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 123 is a reflection nebula in Serpens, 1,430 light-years away
vdB 123 is a reflection nebula in the constellation Serpens, 1,430 light-years away. spans 6.8′ of sky, about 2.8 light-years across. It is a telescope object, 6 inches or larger, and it is highest in the evening sky in August.
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 123 is vdB 123 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 170634, B8/9(IV), magnitude 9.8. He rated it moderate in brightness and moderately blue in color.
Finding vdB 123 from η Ser
vdB 123 lies 4.7° northeast of η Ser, the magnitude 3.2 star. Three fingers held at arm's length cover about 5°.
vdB 123 is highest in the evening in August
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 89°S.
vdB 123 is 1,430 light-years away
The light seen from vdB 123 tonight left it about 1,430 years ago, around 596 AD. It ranks 78 of 158 by distance among the Van den Bergh nebulae. Distance source: Gaia DR3 parallax of the illuminating star via AT-HYG v3.2 (438 pc).
