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Galactic Center

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#1 Sofee12

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Posted 09 September 2023 - 01:23 PM

Recently I had the idea of sketching the field of the galactic center just for the novelty.  Not that anything more than the field stars would be visible.  But what are the coordinates of the galactic center??  Is Sagittarius A at the center of the galaxy??  Is the galactic center a separate location with Sagittarius A slightly offset??  J2000.0 or mean to the current date coordinates??  From the general consensus and the information I've found, Sagittarius A and the galactic center are at 2 different coordinates, separated by about 4 and a half arc-minutes.  Is that correct??  Can anyone supply the coordinates with absolute certainty??

 

Thanks!!



#2 ngc7319_20

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Posted 09 September 2023 - 02:07 PM

Several eons ago I worked on this, so will comment.  Sagittarius A is a very large radio source with filaments, extended emission, etc.  Sagittarius A* is the compact radio source within Sagittarius A.  It is associated with the black hole. That is probably what you want to sketch for your project.  Just google Sagittarius A* or Sgr A* and use those coords.

 

However, none of the stuff at the center can be seen at visible wavelengths.  I tried very hard with the Palomar 200 inch and Hubble Space Telescope a long time ago.  There is just too much dust between here and the center.  There is something like 30 magnitudes of absorption in the visible.


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#3 Keith Rivich

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Posted 09 September 2023 - 02:39 PM

Recently I had the idea of sketching the field of the galactic center just for the novelty.  Not that anything more than the field stars would be visible.  But what are the coordinates of the galactic center??  Is Sagittarius A at the center of the galaxy??  Is the galactic center a separate location with Sagittarius A slightly offset??  J2000.0 or mean to the current date coordinates??  From the general consensus and the information I've found, Sagittarius A and the galactic center are at 2 different coordinates, separated by about 4 and a half arc-minutes.  Is that correct??  Can anyone supply the coordinates with absolute certainty??

 

Thanks!!

I found a couple of sites that seemed to match on coordinates:

 

Rotational center: 17 45 40  -29 00 28

Sag A*                  17 45  04   -29 00 28



#4 Sofee12

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Posted 09 September 2023 - 03:08 PM

Thanks.

 

A friend suggested that there was a difference and that Sagittarius A was not at the galactic center.  The galactic center, which is also the barycenter, or center of rotation, is at a different location than Sagittarius A.  I was just curious to see what others might say, more importantly what the coordinates were.

 

Keith, the coordinates for the rotational center or barycenter that I came up with are what you suggested.  However, the coordinates for Sagittarius A that I got (with the help of the image from Aladin) is:  17h 47m 9.8s  -29 1' 0".

 

I found the area while out observing on 2 Sept. and made a sketch with the star TYC 6840-0564-1 at center.  It just so happened that doing it that way brought both the apparent locations of Sagittarius A and the galactic center within the field of view and the sketch.  BTW, there are 3 stars at TYC 6840-0564-1 within 8 arc-seconds.  I was only able to see 2 of the 3 stars because of the seeing at the low altitude.


Edited by Sofee12, 09 September 2023 - 03:50 PM.

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#5 Sofee12

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Posted 09 September 2023 - 03:51 PM

Additionally....

 

In Cartes du Ciel, the galactic center is labeled "GALCENTER" and IDed as PGC 3098471.  As my friend stated, apparently that's the PGC ID for the Milky Way!!  In Sky Safari Pro, there's no listing for PGC 3098471.  Stellarium searches SIMBAD which shows nothing as well.  Hyperleda gives the coordinates 17h 45m 34.62s  -28 56' 10.0', which are the J2000.0 coordinates in Cartes du Ciel for "GALCENTER"/PGC 3098471.



#6 maroubra_boy

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Posted 09 September 2023 - 05:18 PM

Here's a suggestion from one fellow sketcher to another.

 

To sketch just a narrow FOV that shows not much else than a smattering of stars - sure there may be a lot of stars, but really the composition is not an exciting one as the attention is in an amorphous point and not an object.

 

HOWEVER, the broader context of where the centre of the MW lies is a MAGNIFICENT area.  And to exploit this to make a far more interesting composition I would suggest using low magnification with a rich field scope (rft).

 

The centre of the MW is not visible, plain & simple.  But the direction in which it lies is spectacular & as far as sketching goes, totally unexploited.   And an rft will show thing that are totally invisible to all other scopes, such as the mottling of the MW & the dark nebulosity that riddles this area!

 

As such a field is extremely rich, there are several ways to overcome the technical challenges.  I LOVE rft's and I LOVE sketching with them, not just my much bigger scopes.  So much so that I only have three things on my "must sketch list", two of which involve an rft and are very rich fields.

 

To encourage you, below is a sketch I did that shows how I overcome the technical challenges.

 

The first is of the Large Magellanic Cloud.  There is NO scope that can  fit the whole thing in the one field of view.  This sucker is HUGE, some 12°+ in diameter.  So I used a 4" f/5 frac (5° TFOV) over four sessions over a year (weather was the factor meaning the time span) and sketched onto a large approx A1 size sheet of black paper.  The first pic shows the whole piece, and the second is a close up showing the detail I put into it.

 

Of course it is impossible to lay down each individual star you will see.  What is more important is laying down those significant ones and then portraying a sense of what is seen by the rest, all those micro, tiny, tiny stars that tease the eye, they can be given a sense of this sensation with technique.  The same with the background mottling.  And the dark nebulosity that can be seen can likewise be both faithfully portrayed or hinted to.

Attached Thumbnails

  • LMC whole LR.JPG
  • LMC close up LR - Copy.JPG

Edited by maroubra_boy, 09 September 2023 - 05:31 PM.

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#7 maroubra_boy

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Posted 09 September 2023 - 05:46 PM

Here's another.

 

Close to the galactic centre in the same area is the Ink Spot, a gorgeous dark nebula right next to a lovely small open cluster, both set against the mass that is the Cloud of Sagittarius.  I did this sketch using a 17.5" dob, but this field is so rich that it is quite unique in the sky and the extended time spent examining this FOV during a sketch reveals an extraordinary amount of detail that would otherwise to unnoticed.

 

Of course I do not know what scopes you have.  So I will suggest go into this piece with an open mind.  A narrow FOV is fine as it will just show a star field behind with the galactic centre lies, but it is just a bunch of stars and a wish.  Or you could grab the bull by the horns and smash out something really special by being a bit more adventurous and going wider in the FOV and make a highlight of what lies in between us and the galactic centre.  Consider what scope you are going to use, even take two if you have more than one, a bunch of eyepieces, and see which combo gives the more appealing, exciting composition.

 

Composition in astro sketching is still relevant.  It means spending a little time looking at the wider context of where any given object lies and positioning it on the page in such a way that makes for the most dynamic, interesting, most "story telling" way.  And it isn't always by putting the object in the centre of the FOV...

 

Alex.

Attached Thumbnails

  • Ink Spot - LR.JPG
  • Ink Spot section - LR-1.jpg

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#8 Napp

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Posted 09 September 2023 - 09:04 PM

As noted above the center of the Milky Way is heavily obscured by dust.  However, there are apparently a few small ‘windows’ into the galactic bulge.  The largest of these is ‘Baade’s Window’.  It’s about 1° across.  It looks into the galactic bulge south of the center.  A couple of globular clusters are in the window including NGC 6522 at 20,000 light years distance.  Refer to an article by Bob King in Sky and Telescope from June 2015 for more info: https://skyandtelesc...ndow0610201506/


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#9 Dave Mitsky

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Posted 09 September 2023 - 10:54 PM

The galactic center in infrared:

 

https://www.nasa.gov...ky-way-s-center

 

https://en.wikipedia..._the_Galaxy.jpg

 

The galactic center in radio:

 

https://apod.nasa.go...d/ap220202.html
 

The galactic center in infrared and x-ray:
 

https://en.wikipedia...–_Composite.jpg
 

The galactic center in radio and x-ray:
 

https://universe.nas...-ray-and-radio/


Edited by Dave Mitsky, 09 September 2023 - 10:56 PM.



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