Omega Centauri: Glittering Southern Giant (2009 March 01)

[bystander]

http://apod.nasa.gov/apod/ap090301.html

http://asterisk.apod.com/vie ... 11&t=15129

[apodman]

Omega Centauri is ... apparent visual magnitude 3.9 ... visible ... with the unaided eye.

Okay, I live well north of the equator, so I have to take someone else's word for it. And I have no trouble comparing magnitudes of stars, planets, moons, and asteroids to guess what will be visible with various sky conditions or in a particular size telescope or binoculars. And the sun and our moon are no problem in any case.

But what of nearby galaxies, nebulae, comets, and clusters? These are distributed objects; that is, their brightness is not concentrated in a point. So here we have cluster Omega Centauri (NGC 5139) about 0.5 degree by 0.5 degree at apparent magnitude 3.9 that I'm told is visible to the naked eye. And I'm familiar with looking at M31 (for example) with the naked eye in various conditions - it is apparent magnitude 4.4 distributed over an area about 1 degree by 3 degrees, several times the size of NGC 5139 (though the size of its nucleus is more comparable in size to NGC 5139), and I would call its nucleus barely visible to the naked eye in average suburban skies.

So I wonder "how visible" NGC 5139 is. Does anyone know of a chart or rule-of-thumb that includes magnitude as well as effective area that I could use to compare apparent magnitudes of distributed objects and get an idea how bright they should look to me? Side-by-side pictures at the same scale and exposure would be great, but that might be asking for too much.

[TBIRD7777]

I think we should correctly call Omega Centauri by it's rightful NGC Number!

NGC 5239 is a small common Spiral Galaxy in Bootes nowhere close to Omega Centauri....

NGC 5139 is the correct classification number for Omega Centauri.

I think I see where the problem might have been........typo!


Thanks! - TBIRD7777

[neufer]

Omega Centauri is ... apparent visual magnitude 3.9 ... visible ... with the unaided eye.

Okay, I live well north of the equator, so I have to take someone else's word for it. And I have no trouble comparing magnitudes of stars, planets, moons, and asteroids to guess what will be visible with various sky conditions or in a particular size telescope or binoculars. And the sun and our moon are no problem in any case.

But what of nearby galaxies, nebulae, comets, and clusters? These are distributed objects; that is, their brightness is not concentrated in a point. So here we have cluster Omega Centauri (NGC 5139) about 0.5 degree by 0.5 degree at apparent magnitude 3.9 that I'm told is visible to the naked eye. And I'm familiar with looking at M31 (for example) with the naked eye in various conditions - it is apparent magnitude 4.4 distributed over an area about 1 degree by 3 degrees, several times the size of NGC 5139 (though the size of its nucleus is more comparable in size to NGC 5139), and I would call its nucleus barely visible to the naked eye in average suburban skies.

So I wonder "how visible" NGC 5139 is. Does anyone know of a chart or rule-of-thumb that includes magnitude as well as effective area that I could use to compare apparent magnitudes of distributed objects and get an idea how bright they should look to me? Side-by-side pictures at the same scale and exposure would be great, but that might be asking for too much.

Did you see Comet Holmes? It's sorta like that after it had expanded some.

http://astroprofspage.com/archives/1311
http://en.wikipedia.org/wiki/17P/Holmes
http://antwrp.gsfc.nasa.gov/apod/ap080205.html
http://antwrp.gsfc.nasa.gov/apod/ap071231.html
http://antwrp.gsfc.nasa.gov/apod/ap071221.html
http://antwrp.gsfc.nasa.gov/apod/ap080119.html
http://antwrp.gsfc.nasa.gov/apod/ap080307.html
http://antwrp.gsfc.nasa.gov/apod/ap071128.html
http://antwrp.gsfc.nasa.gov/apod/ap081024.html

[apodman]

NGC 5239 is a small common Spiral Galaxy in Bootes nowhere close to Omega Centauri....
NGC 5139 is the correct classification number for Omega Centauri.

Thanks for the correction, since I duplicated APOD's typo four times. I bought it hook, line, and sinker. And now I see I have been quoted myself. Neufer, please edit the quote and make me look good. Trust but verify.

---

More Omega Centauri APODs:

http://antwrp.gsfc.nasa.gov/cgi-bin/apo ... a+centauri

[neufer]

http://apod.nasa.gov/apod/ap090301.html

[O]mega [C]entauri
in some ways resembles our own
[O]ort [C]loud

[neufer]

Omega Centauri: http://antwrp.gsfc.nasa.gov/apod/ap080501.html
http://antwrp.gsfc.nasa.gov/apod/ap001015.html
http://antwrp.gsfc.nasa.gov/apod/ap011010.html

47 Tuc: http://antwrp.gsfc.nasa.gov/apod/ap050721.html
http://antwrp.gsfc.nasa.gov/apod/ap980203.html
http://antwrp.gsfc.nasa.gov/apod/ap010524.html
http://antwrp.gsfc.nasa.gov/apod/ap071001.html
http://antwrp.gsfc.nasa.gov/apod/ap080826.html
http://antwrp.gsfc.nasa.gov/apod/ap050617.html

M25: http://antwrp.gsfc.nasa.gov/apod/ap030411.html

[neufer]

M15 planetary nebula: http://antwrp.gsfc.nasa.gov/apod/ap000804.html
M15 X-Ray Stars: http://antwrp.gsfc.nasa.gov/apod/ap010920.html
http://antwrp.gsfc.nasa.gov/apod/ap011210.html

M13: http://antwrp.gsfc.nasa.gov/apod/ap070518.html
http://antwrp.gsfc.nasa.gov/apod/ap071115.html
http://antwrp.gsfc.nasa.gov/apod/ap050313.html

M22 planets?: http://antwrp.gsfc.nasa.gov/apod/ap010703.html
http://antwrp.gsfc.nasa.gov/apod/ap050627.html

M9, M22, M28, M54, M69, M70: http://antwrp.gsfc.nasa.gov/apod/ap011229.html

[neufer]

M55: http://antwrp.gsfc.nasa.gov/apod/ap000922.html
http://antwrp.gsfc.nasa.gov/apod/ap010223.html
http://antwrp.gsfc.nasa.gov/apod/ap080402.html

Blue Stragglers: http://antwrp.gsfc.nasa.gov/apod/ap000622.html
http://antwrp.gsfc.nasa.gov/apod/ap990707.html
NGC 6397: http://antwrp.gsfc.nasa.gov/apod/ap030808.html

M10: http://antwrp.gsfc.nasa.gov/apod/ap010630.html

Globular Cluster in M31: http://antwrp.gsfc.nasa.gov/apod/ap981017.html
http://antwrp.gsfc.nasa.gov/apod/ap030519.html
Globular Cluster in M33: http://antwrp.gsfc.nasa.gov/apod/ap980721.html

[neufer]

M4: http://antwrp.gsfc.nasa.gov/apod/ap030718.html
http://antwrp.gsfc.nasa.gov/apod/ap070903.html

M3 RR Lyrae stars: http://antwrp.gsfc.nasa.gov/apod/ap070415.html
http://antwrp.gsfc.nasa.gov/apod/ap070609.html

M2: http://antwrp.gsfc.nasa.gov/apod/ap010611.html

Young Globular Clusters:
NGC 2903: http://antwrp.gsfc.nasa.gov/apod/ap010321.html
NGC 1569: http://antwrp.gsfc.nasa.gov/apod/ap081229.html
LMC: http://antwrp.gsfc.nasa.gov/apod/ap001224.html
http://antwrp.gsfc.nasa.gov/apod/ap080806.html
SMC: http://antwrp.gsfc.nasa.gov/apod/ap020719.html

[neufer]

NGC 6934: http://antwrp.gsfc.nasa.gov/apod/ap990630.html
NGC 6723: http://antwrp.gsfc.nasa.gov/apod/ap060115.html
NGC 6712: http://antwrp.gsfc.nasa.gov/apod/ap990225.html
NGC 4697: http://antwrp.gsfc.nasa.gov/apod/ap020617.html
NGC 4372: http://antwrp.gsfc.nasa.gov/apod/ap081208.html
NGC 1316: http://antwrp.gsfc.nasa.gov/apod/ap080902.html

Palomar 13: http://antwrp.gsfc.nasa.gov/apod/ap030125.html

NGC 1316: http://antwrp.gsfc.nasa.gov/apod/ap050404.html

[neufer]

M87: http://antwrp.gsfc.nasa.gov/apod/ap040616.html
http://antwrp.gsfc.nasa.gov/apod/ap000706.html

Oblong M19: http://antwrp.gsfc.nasa.gov/apod/ap000719.html

Intergalactic Wanderer: http://antwrp.gsfc.nasa.gov/apod/ap090123.html
http://antwrp.gsfc.nasa.gov/apod/ap051122.html

Model: http://antwrp.gsfc.nasa.gov/apod/ap020730.html

[neufer]

http://apod.nasa.gov/apod/ap090301.html

[O]mega [C]entauri:

• ------------------------------------------
  Omega Centauri Radius ~86.0 ly
  Typical Orbital Period: ~ 2,500,000 years
  Total System Mass ~5,000,000 solar masses
  ------------------------------------------

in some ways resembles our own
[O]ort [C]loud:

• ------------------------------------------
  Oort Cloud Radius: ~0.86 ly
  Typical Orbital Period: ~2,500,000 years
  Total System Mass: ~ 1 solar masses (i.e., Sol itself)
  ------------------------------------------

Average Density = { [197 min./Orbital Period]^2 } g/cm³

[TBIRD7777]

In over three years of tracking APOD everyday I have never known them to miss-classify a deep-sky object. So my first post to this forum was to point one out? I think I would be remiss not to give them a hand for that and for quickly correcting Saturday's Typo.......

TBIRD7777