Dark nebulae are not as popular and spectacular as emission or reflection nebulae, but still, there are many astronomy amateurs who are fascinated by them. The line between the reflection and the dark nebula is not that obvious. A reflection nebula is a cloud of dust illuminated by nearby stars. A pure dark nebula on the other hand cannot be detected unless there is something bright in the background. So, as long as we have distant stars or other luminous nebulae, we can observe dark nebula that obscures more distant objects. But there is not a common scenario that a dark cloud is not illuminated at all. If there are no nearby stars to do that task, there are always some more distant stars. So that dark cloud will always be illuminated by something, although this something may be far away and may provide very little light. This way all dark nebulae are in some way also reflection nebulae, however, it is not always possible to capture this reflectivity in a reasonable exposure time.
The two dark clouds presented below are typical dark ones. Barnard 171 is the one cataloged by Edward Emerson Barnard at plate nr 49. You can find it in the constellation of Cepheus. Determining the distance to the dark cloud is not a trivial task, because we do not have any point of reference that actually radiates any information directly, so I was not able to find any information about how far away is that dark cloud.
There are several other dark nebulae in the frame – the most prominent is probably Barnard 174 at the left part of the frame, which is an active star formation region. Barnards 169, 170, and 173 are also captured in the image below. The bright star in the lower left part is Zeta Cephei – an orange supergiant about 3,600 times more luminous than Sun, that is located about 840 light-years away from us.
There is another dark nebulae catalog that contains a larger number of them – Lynds’ Dark Nebula catalog – LDN. The next image target is located in the constellation of Aquila some 300-600 light-years from us and is cataloged as LDN673. This dark nebula is a part of the so-called Aquila Rift which is a great mass of dark molecular clouds along the summer Milky Way that passes over the constellations Aquila, Serpens, and Ophiuchus. If you take a closer look at the image you will spot a small reflective object a little bit to the left of the image center. It is Herbig Haro object HH32 located about 900 light-years away. HH32 is a jet of the matter traveling at about 320km/s and most probably comes from the young T Tauri type star nearby.
A faint and not well-defined bunch of stars close to the right image frame is Berkeley 43 open cluster about 4,000 light-years away.
Image technical data: Date: November 2022 Location: Nieborowice, Poland Telescope: TecnoSky 90/540 Owl triplet Corrector: TS FF/FR 0.8x Camera: QHY268M Mount: EQ6 Guiding: ASI290MM + Evoguide ED50 Exposure: each image is about 6 hours of total exposure time with LRGB Baader filters Conditions: Bortle 6, transparency medium-good, seeing medium
