Barnard 68

Barnard 68 is a molecular cloud, a dark absorbing nebula or Bok's globule, located in the direction of the southern constellation Ophiuchus and within the Milky Way galaxy at a distance of about 125 parsecs (407 light-years). It is so close and dense that the stars behind it are not visible from Earth. American astronomer Edward Emerson Barnard added this nebula to his catalog of dark nebulae in 1919. Its catalog was published in 1927 and at this stage it included about 350 objects.. Because of its opacity, its interior is very cold, its temperature being around 16 K (-257 °C/-431 °F). Its mass is about twice that of the Sun, and its diameter is about half a light year.

Observation

This nebula can be found in the south of the constellation Ophiuchus, the nearest bright star is 191 Ophiuchus, other bright stars around are 44 Ophiuchus, Theta Ophiuchus, Omicron Ophiuchus and HD 157398. This nebula is also designated as LDN 57 and [CB88] 82.

The coordinates of this dark nebula are:

1. Right ascension: 17 22 38.2
2. Declination: -23 49 34
3. Galactic longitude: 001.5249
4. Galactic latitude: +07.0895

Position in the Sky

This photo shows where the Barnard 68 Nebula is located: File:Barnard68sky.png Barnard 68 location: File:Barnard68place.png

Maps and photos

photo of Barnard 68 from Sky Map.org: File:Barnard68photo.png beautiful photo of Barnard 68: File:Barnard68beautifulphoto.jpg

Characteristics

Although it is opaque to visible wavelengths, use of the Very Large Telescope at the Cerro Paranal revealed the presence of about 3,700 blocked background stars in the Milky Way, about 1,000 of which are visible in the infrared. Careful measurements of the degree of obscuration resulted in an accurate mapping of the distribution of dust within the cloud. Observations obtained by the Herschel space observatory made it possible to further limit the distribution of the dust component and its temperature. The presence of a dark cloud in the vicinity of the Sun greatly facilitates observation and measurement. If external forces do not disturb the stability of dust clouds, then it is a fine balance between external pressure caused by the heat or pressure of the cloud contents and internal gravitational forces generated by the same particles (see Jeans instability and Bonnor-Ebert mass). This causes the cloud to sway or oscillate, like a large soap bubble or a water-filled balloon that sways. For the cloud to become a star, gravity must take over long enough to cause the cloud to collapse and reach a temperature and density at which fusion can be sustained. When this happens, the star's much smaller envelope signals a new balance between greatly increased gravity and radiation pressure. The mass of the cloud is about twice the mass of the Sun, and its diameter is about half a light year. The well-defined edges and other features of Barnard 68 show that it is on the verge of gravitational collapse, followed by stellar transformation over the next 200,000 years or so. The cloud is often confused with the Bootes Void, although there is nothing in common between the two, and images of Barnard 68 are often erroneously used to illustrate articles on the Bootes Void.