Starship Asterisk*

... half a light-year across. It is not known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely places for new stars to form. In fact, Barnard 68 itself has been found likely to collapse and form a new star system.

vdix wrote: ↑Sun Nov 22, 2020 11:00 am 500 light year away in that direction and there are no stars in front of it? That seems unlikely.

BDanielMayfield wrote: ↑Sun Nov 22, 2020 12:54 pm

vdix wrote: ↑Sun Nov 22, 2020 11:00 am 500 light year away in that direction and there are no stars in front of it? That seems unlikely.

But this cloud is very small as these objects go, being "only half a light year across." Something that small even at that distance could easily have no stars between us and it. Space is mostly empty. The average spacing between neighboring star systems around here is, what, about 5 ly or so.

Barnard 68 is a molecular cloud, dark absorption nebula or Bok globule, towards the southern constellation Ophiuchus and well within our own galaxy at a distance of about 400 light-years, so close that not a single star can be seen between it and the Sun.

Stellar density is the average number of stars within a unit volume. It is similar to the stellar mass density, which is the total solar masses (MSun) found within a unit volume. Typically, the volume used by astronomers to describe the stellar density is a cubic parsec (pc³).

In the solar neighborhood, this value can be determined from surveys of nearby stars, combined with estimates of the number of faint stars that may have been missed. The true stellar density near the Sun is estimated as 0.004 stars per cubic light year, or 0.14 stars pc³.

It is possible to look right through the cloud in infrared light.

BDanielMayfield wrote: ↑Sun Nov 22, 2020 5:57 am

... half a light-year across. It is not known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely places for new stars to form. In fact, Barnard 68 itself has been found likely to collapse and form a new star system.

This then is proof that not all stellar systems form in groups, some stars can and do form by themselves. Interesting. Is solo system formation rare or common?

orin stepanek wrote: ↑Sun Nov 22, 2020 1:53 pm barnard68v2_vlt_960.jpg


Kinda spooky little Twerp! It's density is so amazing
that it hides all the stars behind it!

It is possible to look right through the cloud in infrared light.

I'd like to see a photo of that; (maybe I missed it!)

jiharmer@hotmail.co.uk wrote: ↑Sun Nov 22, 2020 5:06 pm Haven't we had this picture on APOD before ? Or am I just going completely bonkers ?

De58te wrote: ↑Sun Nov 22, 2020 5:48 pm

jiharmer@hotmail.co.uk wrote: ↑Sun Nov 22, 2020 5:06 pm Haven't we had this picture on APOD before ? Or am I just going completely bonkers ?

2017, October 08. And the comments there said it was also from 2014, December 14.

BDanielMayfield wrote: ↑Sun Nov 22, 2020 1:33 pm Stellar density in solar neighborhood is only 0.004 stars per cubic light year

Stellar density is the average number of stars within a unit volume. It is similar to the stellar mass density, which is the total solar masses (MSun) found within a unit volume. Typically, the volume used by astronomers to describe the stellar density is a cubic parsec (pc³).

In the solar neighborhood, this value can be determined from surveys of nearby stars, combined with estimates of the number of faint stars that may have been missed. The true stellar density near the Sun is estimated as 0.004 stars per cubic light year, or 0.14 stars pc³.

The volume of a cone with a length of 400 LY and a base of 0.25 LY is only about 26 LY³. The odds of a star being between us and an object as small as Barnard 68 is only 0.004*26 or about 0.104 to 1.

heehaw wrote: ↑Sun Nov 22, 2020 6:07 pm

De58te wrote: ↑Sun Nov 22, 2020 5:48 pm

jiharmer@hotmail.co.uk wrote: ↑Sun Nov 22, 2020 5:06 pm Haven't we had this picture on APOD before ? Or am I just going completely bonkers ?

2017, October 08. And the comments there said it was also from 2014, December 14.

I LOVE seeing a great APOD, such as this one, every so often!

johnnydeep wrote: ↑Sun Nov 22, 2020 6:29 pm

BDanielMayfield wrote: ↑Sun Nov 22, 2020 1:33 pm Stellar density in solar neighborhood is only 0.004 stars per cubic light year

Stellar density is the average number of stars within a unit volume. It is similar to the stellar mass density, which is the total solar masses (MSun) found within a unit volume. Typically, the volume used by astronomers to describe the stellar density is a cubic parsec (pc³).

In the solar neighborhood, this value can be determined from surveys of nearby stars, combined with estimates of the number of faint stars that may have been missed. The true stellar density near the Sun is estimated as 0.004 stars per cubic light year, or 0.14 stars pc³.

The volume of a cone with a length of 400 LY and a base of 0.25 LY is only about 26 LY³. The odds of a star being between us and an object as small as Barnard 68 is only 0.004*26 or about 0.104 to 1.

Thanks for that extra math! I too couldn't quite believe there were no stars between us and Barnard 68. BTW, I just double checked your local stellar density figure using numbers from http://www.atlasoftheuniverse.com/250lys.html, which says there are about 260000 stars within 250 ly, which is 6.54e7 ly ³. That amounts to almost exactly .004 stars / ly³. What a pleasant coincidence!

There Are About 260000 Stars Within 250 Light Years Of US

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E Fish wrote: ↑Sun Nov 22, 2020 3:34 pm

orin stepanek wrote: ↑Sun Nov 22, 2020 1:53 pm barnard68v2_vlt_960.jpg


Kinda spooky little Twerp! It's density is so amazing
that it hides all the stars behind it!

It is possible to look right through the cloud in infrared light.

I'd like to see a photo of that; (maybe I missed it!)

The ESO has a series of images of Barnard 68 in different wavelengths. B&W but still neat to see. https://www.eso.org/public/images/eso9934b/

De58te wrote: ↑Sun Nov 22, 2020 5:48 pm

jiharmer@hotmail.co.uk wrote: ↑Sun Nov 22, 2020 5:06 pm Haven't we had this picture on APOD before ? Or am I just going completely bonkers ?

2017, October 08. And the comments there said it was also from 2014, December 14.

BDanielMayfield wrote: ↑Sun Nov 22, 2020 10:10 pm
In honor of all who mainly comment on what some object in an APOD looks like,

Barn[y]ard 68 resembles a cow paddy after it's been stepped in.

Perhaps it smells like a barnyard too. (All those aromatic hydrocarbons, etc.)

• A remnant of rector Poczobutt's Taurus Poniatovii

https://en.wikipedia.org/wiki/Taurus_Poniatovii wrote:

Ophiuchus holding the serpent, Serpens, as depicted in Urania's Mirror, a set of constellation cards published in London c. 1825. Above the tail of the serpent is the now-obsolete constellation Taurus Poniatovii

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<<Taurus Poniatovii (Latin for Poniatowski's bull) was a constellation created by the former rector of Vilnius University, Marcin Odlanicki Poczobutt, in 1777 to honor Stanislaus Poniatowski, king of Poland. It consisted of stars that are today considered part of Ophiuchus and Aquila. It is no longer in use. It was wedged in between Ophiuchus, Aquila and Serpens Cauda. A depiction of the constellation can be found on the wall of the Vilnius University Astronomical Observatory.

The stars were picked for the resemblance of their arrangement to the Hyades group which form the "head" of Taurus. Before the definition of Taurus Poniatovii, some of these had been part of the obsolete constellation River Tigris. The brightest of these stars is 72 Oph (3.7 magnitude) in the "horn" of Taurus Poniatovii. The "face" of Taurus Poniatovii is formed by 67 Oph (4.0), 68 Oph (4.4) and 70 Oph (4.0).[1] The five brightest stars belong to loose open cluster Collinder 359 or Melotte 186. Barn(y)ard's star is also inside the boundaries of this former constellation. Some minor stars (5th and 6th magnitude) now in Aquila formed the "rear" of Taurus Poniatovii.>>