The Snake Nebula (Barnard 72) is a small dark cloud in the constellation Ophiuchus. It has a distinct S shape and meanders across the sky against the golden backdrop of a dense part of our Milky Way galaxy. The darker and more compact Barnard 68 is at the bottom right, appearing as a prey within the grasp of the lurking celestial snake!
Both these nebulae are dark absorption clouds of molecular gas and dust. Barnard 68 is located 500 light years away and contains about two solar masses of material within half a light-year. It is on the verge of collapsing under its own gravity to become a star and may do so within the next 200,000 years.
These interstellar clouds are sufficiently dense to block the light from thousands of background stars in the direction towards our galactic centre.
There exist many dark patches such as this one and the most famous is without doubt the Horsehead Nebula in Orion. Another and much larger example, visible to the naked eye when away from city lights, is the large dark patch near the Southern Cross known as the Coalsack Nebula. These clouds are full of tiny dust particles, each less than a micrometre in size. Optical wavelengths are easily absorbed by this dust and therefore the nebulae appear dark against any background light. However, radio and infrared wavelengths can penetrate the clouds and allow a peek inside where star formation often occurs.

In the early 1900's the American astronomer Edward Emerson Barnard complied a catalogue of dark nebulae by studying his many photographs of the Milky Way. Barnard was also an avid visual observer and discovered 15 comets, Jupiter's small moon Amalthea and Barnard's Star the second closest star to our solar system. He also made fleeting observations of so-called 'spokes' in Saturn's rings; a mysterious phenomenon only confirmed much later when the Voyager 1 space probe passed Saturn in 1980.

Image details:
Date: March-May 2022
Exposure: LRGB: 355:125:115:115 mins, total 11 hours 50 mins @ -25C
Telescope: Homebuilt 12.5" f/4 Serrurier Truss Newtonian
Camera: QSI 683wsg with Lodestar guider
Filters: Astrodon LRGB E-Series Gen 2
Taken from my observatory in Auckland, New Zealand