<p>Not noticeably darker.</p>

<p>Assuming such a globule has a mass of 50 solar masses and a diameter of 1 light year, that would make it's average density about <span class="math-container">$2.2\times 10^{-16}\,kg\,m^{-3}$</span> which is fairly close to not being there at all in human terms.</p>

<p>An imaginary tube of this stuff 1 AU tall and of area 1 meter squared would contain about <span class="math-container">$3\times 10^{-5}\,kg$</span> of mass.  That is an imaginary tube from Earth to the Sun.</p>

<p>That much matter won't block much light.</p>

<p>For comparison the density of air at ground level is about <span class="math-container">$1.2\,kg\,m^{-3}$</span>.  So less than a millimeter of air at ground level blocks more sunlight than the dust cloud would.</p>

<p>Also </p>

CC BY-SA 4.0
2018-10-03T02:42:38.963Z
Question calls them "dust clouds" and Wikipedia says about 1% dust. I think this won't change "Not noticeably darker." but the dust particles may be more important to the answer than the gaseous components of the cloud.
uhoh
CC BY-SA 4.0
2018-10-03T12:00:00.887Z
Presumably, though, gravitational effects would make the cloud concentrate in the inner solar system?
adrianmcmenamin
CC BY-SA 4.0
2018-10-03T16:49:24.983Z
@uhoh I think it makes no difference as the total mass "in the way" won't change no matter what it's made of.
StephenG - Help Ukraine
CC BY-SA 4.0
2018-10-03T16:52:28.750Z
@StephenG I don't think that's how astronomers handle dust, just saying it's the same as an equivalent amount of gas. In this particular case with such a short path length and low density, doing this wrong will still give a reasonable answer, but it's still not correct to suggest dust can be treated as gas.
uhoh
CC BY-SA 4.0
2018-10-03T16:55:13.863Z
@adrianmcmenamin I'm not at all clear on how the cloud would interact with the Sun's solar wind (and the "bow shock" where the Sun's solar wind meets the interstellar medium).  This might reduce the extent to which the cloud can penetrate, although we're talking about very low densities anyway in human terms.
StephenG - Help Ukraine
CC BY-SA 4.0
2018-10-03T16:57:35.287Z
@uhoh I didn't make any attempt to treat the cloud in any detailed way, and you should view my estimate as strictly "back of the envelop" stuff.  If I'm within a couple of orders of magnitude I'd be happy.
StephenG - Help Ukraine
CC BY-SA 4.0
2018-10-02T22:04:22.720Z
2018-10-02T22:04:22.720Z
StephenG - Help Ukraine
<p>Bart Bok gave his name to dust clouds of 2-50 solar masses, which by their darkness may be 100 times more frequent than telescopes can detect. </p>

<p>If the solar system traversed a <a href="https://en.wikipedia.org/wiki/Bok_globule" rel="nofollow noreferrer">Bok Globule</a>, how dark would the sun become towards the surface of the Earth, as visible by humans? </p>

<radiation><nebula><interstellar-medium><dust>
How dark would the sun become if we traversed a Bok globule?
bandybabboon
# How dark would the sun become if we traversed a Bok globule?

(Asked by: username_0 on 2018-10-02)

Bart Bok gave his name to dust clouds of 2-50 solar masses, which by their darkness may be 100 times more frequent than telescopes can detect.

If the solar system traversed a [Bok Globule](https://en.wikipedia.org/wiki/Bok_globule), how dark would the sun become towards the surface of the Earth, as visible by humans?

**Tags:** radiation, nebula, interstellar-medium, dust


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## 1 answers

### Answer by username_1 on 2018-10-02. Score: 4 | Accepted answer

Not noticeably darker.

Assuming such a globule has a mass of 50 solar masses and a diameter of 1 light year, that would make it's average density about $2.2\times 10^{-16}\,kg\,m^{-3}$ which is fairly close to not being there at all in human terms.

An imaginary tube of this stuff 1 AU tall and of area 1 meter squared would contain about $3\times 10^{-5}\,kg$ of mass. That is an imaginary tube from Earth to the Sun.

That much matter won't block much light.

For comparison the density of air at ground level is about $1.2\,kg\,m^{-3}$. So less than a millimeter of air at ground level blocks more sunlight than the dust cloud would.

Also

> **Comments:**
> **username_2**: Question calls them "dust clouds" and Wikipedia says about 1% dust. I think this won't change "Not noticeably darker." but the dust particles may be more important to the answer than the gaseous components of the cloud.  
> **username_3**: Presumably, though, gravitational effects would make the cloud concentrate in the inner solar system?  
> **username_1**: @username_2 I think it makes no difference as the total mass "in the way" won't change no matter what it's made of.  
> **username_2**: @username_1 I don't think that's how astronomers handle dust, just saying it's the same as an equivalent amount of gas. In this particular case with such a short path length and low density, doing this wrong will still give a reasonable answer, but it's still not correct to suggest dust can be treated as gas.  
> **username_1**: @username_3 I'm not at all clear on how the cloud would interact with the Sun's solar wind (and the "bow shock" where the Sun's solar wind meets the interstellar medium).  This might reduce the extent to which the cloud can penetrate, although we're talking about very low densities anyway in human terms.  
> **username_1**: @username_2 I didn't make any attempt to treat the cloud in any detailed way, and you should view my estimate as strictly "back of the envelop" stuff.  If I'm within a couple of orders of magnitude I'd be happy.  

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