LBN691, a "bright" nebula

5/24

ASI2600MM, 360mm f/2.8, 18.7h (RGB 3x1.5h, Lum 14.3h)

Based on the sky survey of the Palomar Observatory around 1950 Beverly Lynds created two catalogs, namely Lynds' Catalogue of Dark Nebulae and Lynds' Catalogue of Bright Nebulae.

The original catalog data may be found online for example at the University of Strasbourg:
Bright Nebulae (LBN) Dark Nebulae (LDN).

In these catalogs dark and bright do not relate to visibility but if the nebula hides light from the background or not.

Examples for dark nebulae with catalogue prefix LDN are LDN1082 resp. B150 or LDN1174 as a dark patch of the Iris Nebula.

Objects with the prefix LBN are brighter than the background. This includes objects like LBN974, the Great Orion Nebula, which may be spotted visually even with smaller telescopes. Others are quite faint and nearly invisible on the plates from the survey, like this LBN691 next to the big dipper.

Scans from the photographic plates (Palomar Observatory Sky Atlas, POSS1) can be downloaded from the archive of the Space Telescope Science Institute. I used 22 Tiles of LBN691 from the blue channel to create the following mosaic matching the same area as the image above (Data use and Copyright by MAST):

My image is the result of several nights during new moon in May 2024. Under my Bortle 5 sky I needed more than 10 hours on luminance to recover the finer structures of this object.

On a closer look you'll find several galaxies in the background.