The sky around LDN 31 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 31 is a dark nebula in Ophiuchus, 450 light-years away
LDN 31 is a dark nebula in the constellation Ophiuchus, 450 light-years away. It covers 0.022 sq deg of sky, about the area of a circle 10′ across, or 1.3 light-years at its distance, and Lynds gave it opacity 6 of 6, the darkest. 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 31 from Antares
LDN 31 lies 8.7° northeast of Antares, the magnitude 1.1 star. A fist held at arm's length covers about 10°.
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 31 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 71°N, and never sets south of 71°S.
LDN 31 is 450 light-years away
The light seen from LDN 31 tonight left it about 450 years ago, around 1576 AD. Distance source: Ophiuchus (B45), Gaia DR2 dust, Zucker et al. 2020 (sightline 2.4 deg away, 139 pc).
3 Lynds bright nebulae and 50 Lynds dark nebulae lie within 5° of LDN 31
