The sky around LDN 121 at true scale, north up and east left, with stars to magnitude 8, the Lynds bright and dark nebulae, and the NGC and IC objects in the field. The box marks a circle of the same area as the cloud; the cloud itself is irregular.
LDN 121 is a dark nebula in the constellation Ophiuchus. It covers 0.017 sq deg of sky, about the area of a circle 8.8′ across, and Lynds gave it opacity 5 of 6, dark. It is a dark patch against the stars at low power in a telescope, under a dark sky, and it is highest in the evening sky in July.
Dark nebula: a cold cloud of gas and dust, a few degrees above absolute zero, dense enough to block the light of the stars behind it. Dark clouds are where new stars form, and they show only by contrast against a rich star field.
Finding LDN 121 from Han
LDN 121 lies 3.5° south of Han, the magnitude 2.5 star. Three fingers held at arm's length cover about 5°.
A dark nebula shows only by contrast, as a patch with fewer stars than the field around it. Use the lowest power and widest field you have, from a dark site with the Milky Way high in the sky; a nebula filter does not help, because there is no light from the cloud to pass.
LDN 121 is highest in the evening in July
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 76°N, and never sets south of 76°S.
The distance to LDN 121 is not well measured
No reliable distance has been measured for it yet.
7 Lynds bright nebulae and 35 Lynds dark nebulae lie within 5° of LDN 121
