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Re: APOD: Galaxy NGC 474: Cosmic Blender (2011 Jul 26)
Posted: Wed Jul 27, 2011 1:51 am
by neufer
alter-ego wrote:
To first order, the airy disk size (diameter of 1st minimum of an airy pattern) remains the same, and, as Chris said, the fraction of power in the central lobe (
Strehl Ratio) goes down for obstructed apertures. Planetary viewing is the classic example for using refractors over obstructed reflectors. The important net result of brighter airy rings is a reduction contrast for details on extended objects, commonly planets with having low contrast featurs (bands, clouds, surface details). Thus it is harder to see low contrast details with an obstructed aperture. I imagine the same could be said for very close binaries or a globular cluster too. The contrast reduction problem applies to all extended objects, just some objects are affected worse. Planets are the classic examples.
This
site shows nice diffraction simulations of obstructed apertures and the convolution of apertures with spiders
Very interesting, alter-ego, thanks.
Of course the largest refractor objectives are far smaller than the secondaries on most reflectors to begin with.
And then there is the critical importance of atmospheric seeing for ground based telescopes without adaptive optics.
Re: APOD: Galaxy NGC 474: Cosmic Blender (2011 Jul 26)
Posted: Wed Jul 27, 2011 2:50 am
by saturn2
Elliptical Galaxy N G C 474 / Diameter 250,000 light years.
Elliptical Galaxy Milky Way / Diameter 100,000 light years.
The halos of large galaxies are the product of the interaction with ( and accretions of ) smaller nearby galaxies.
The accretion of matter is very forte.
Re: APOD: Galaxy NGC 474: Cosmic Blender (2011 Jul 26)
Posted: Wed Jul 27, 2011 5:06 pm
by Scott Souza
I wonder if this galaxy has a name. If not I'd like to propose 'The Mushroom Galaxy.' It has three or four large structures emerging from various points which look like mushrooms to my eye. - Scott Souza
Re: APOD: Galaxy NGC 474: Cosmic Blender (2011 Jul 26)
Posted: Wed Jul 27, 2011 5:27 pm
by Tarree
Any possibility that we are viewing the 474 with an intervening black hole and the visual effects are caused by gravity lensing?
Yes, I am a newbie.
Re: APOD: Galaxy NGC 474: Cosmic Blender (2011 Jul 26)
Posted: Wed Jul 27, 2011 5:57 pm
by Ann
JLSmith wrote:To my view the spiral galaxy above NGC 474 mentioned in the article looks remarkably unaffected to be under going a collision/gravational interaction with the much larger NGC 474. I don't see any extended tidal tails or other effects; maybe a little bending in the outer arms. If these galaxys were actually interacting wouldn't the smaller galaxy be more affected?
These two galaxies aren't interacting very much. The shells and jets of NGC 474 were almost certainly caused by at least one past merger with a smaller galaxy, which has now been consumed.
Tarree wrote:
Any possibility that we are viewing the 474 with an intervening black hole and the visual effects are caused by gravity lensing?
An intervening black hole wouldn't cause that sort of visual distortions in a galaxy. Check out this page to see what kind of visual effects would be caused by an intervening black hole:
http://www.sciencephoto.com/media/334002/enlarge.
Ann
Re: APOD: Galaxy NGC 474: Cosmic Blender (2011 Jul 26)
Posted: Wed Jul 27, 2011 6:07 pm
by Tarree
Got it, thanks.