Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Avg density of nebula?

NV
  • Please log in to reply
5 replies to this topic

#1 Jim4321

Jim4321

    Soyuz

  • -----
  • topic starter
  • Posts: 3574
  • Joined: 19 Sep 2014
  • Loc: Asheville

Posted 19 September 2019 - 08:02 AM

(Mods, this may be a better fit in Outreach or some other forum; feel free to move it, but it arises from using a NVD.)

 

It looks like our scheduled outreach at our shared club / university observatory will happen tomorrow.  I'll be using my 9.25 Evolution.  At full dark, I plan to change over to a focal reducer and Mod 3, and spend the rest of the evening on M8, probably with a 7 or 12 nm H-a filter.   I like to make visits to my 'scope at least somewhat educational.

 

I'd like to know what the average / typical density of hydrogen gas is in a nebula like M8, in terms at least some of the general public can maybe understand.  I find that units like 'molecules per cubic meter' just go right past most folks (me included, often).   

 

Is there some easily-grasped number like  '1/10 the density of air at some XX altitude', or some other number and unit?

 

TIA!

 

Jim H.



#2 chemisted

chemisted

    Mariner 2

  • -----
  • Posts: 268
  • Joined: 24 Feb 2012

Posted 19 September 2019 - 08:17 AM

Jim,  I don't think you want to go there.  The hydrogen in nebulae is atomic hydrogen as opposed to molecular hydrogen that we use on Earth.  Those atoms are spread out and although I don't know the exact density it has to be an exceptionally small number.  I would just stick with it is the most abundant element in the universe and was created in the Big Bang event.  Ed



#3 mashirts

mashirts

    Messenger

  • *****
  • Posts: 429
  • Joined: 18 Sep 2014
  • Loc: Elgin, TX

Posted 19 September 2019 - 09:52 AM

10,000 per cubic centimeter for bright nebula. The outermost layer of atmosphere the exosphere is like a million per cubic centimeter. Exosphere is above 600km. So the nebula gas is very un-dense by earth/solar system standards.

Not an expert. Google searches.

#4 OleCuss

OleCuss

    Vanguard

  • *****
  • Posts: 2452
  • Joined: 22 Nov 2010

Posted 19 September 2019 - 09:57 AM

They are so diffuse that if you were in a nebula you would not be able to tell.  Oh, you might see the nebula in the distance and figure out that you must be in one, but you just wouldn't see it at all in your immediate vicinity.



#5 mashirts

mashirts

    Messenger

  • *****
  • Posts: 429
  • Joined: 18 Sep 2014
  • Loc: Elgin, TX

Posted 19 September 2019 - 09:58 AM

Source of exosphere density figures:

https://www.thoughtc...d-facts-4129101

#6 StupendousMan

StupendousMan

    Mariner 2

  • -----
  • Posts: 205
  • Joined: 21 Aug 2005

Posted 22 September 2019 - 06:04 PM

The following is off by a few orders of magnitude, but it might help to give people a decent idea of the low densities in space.

 

Hand a visitor an ordinary die (which is roughly 1 cubic centimeter in volume).  Tell the visitor that here on Earth, the number of air molecules within that volume is about the same as the number of all the humans who have ever lived on Earth; while in space, in the middle of an HII region, the number of hydrogen atoms in that same volume is about 1.

 

(This underestimates both values by about a factor of 1000, but the ratio is about right, and it ought to make a pretty good impression.)

 

Give it a try next time.


  • russell23 and Jim_V like this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: NV



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics