NEBULAE
Shark Nebula
— LDN 1235 —
Processed by Nicolas Rolland, Paris. 15 hours gathered by Demoniak Alexkid in France.
There is nothing to see here, and that is the subject. This shape is drawn entirely by what it hides.
A dark nebula in Cepheus
LDN 1235 sits about 650 light-years away in Cepheus, and it emits nothing at all. It is interstellar dust, dense enough to absorb the visible light of whatever lies behind it — the same kind of cloud as the Horsehead in Orion or the Cone in Monoceros. Its entry in the Lynds Catalog of Dark Nebulae, an updated version of the list Beverly Lynds published in 1962, is the only designation it carries.
Why the shape reads as a fin
A dark nebula has no outline of its own. What draws the shark is the density of the dust changing from one place to the next: where the cloud thickens, fewer background stars come through, and the eye reads the gap as an edge. The brighter patches within the cloud are not lit from inside — they are simply thinner. Every contour in this image is a measurement of how much is in the way.
Four degrees of sky
The field runs 3.9 by 2.7 degrees, close to eight full Moons across. That is what it takes to hold the whole cloud, and it is unusual for a target this faint: most deep-sky work trades field for reach. Here the two had to be held together, because a fragment of this shape would not read as anything.
Fifteen hours from the Ardèche
The data came from an ASKAR 400 working at f/5.6 in the Ardèche in August 2021, under a Bortle 4 sky. Two cameras shared the work: an ASI 2600MM behind a luminance filter for ten hours, and an ASI 2600MC for five hours of colour. That split is the whole strategy — a dark nebula is a contrast problem before it is a colour problem, and the ten hours of monochrome luminance are what separate the dust from the sky behind it. Bortle 4 sets the floor: the faintest outer wisps sit close to the background, and pushing them further would have brought the sky up with them. The colour, gathered in a third of the time, is enough to say that the cloud is brown and not much more. Demoniak Alexkid gathered the data.
