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Urban Imaging: Objects in Cygnus

By David Nakamoto
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In my previous articles on urban imaging, I gave some strategies to increase your chances of imaging deep sky objects. I’d like to give my personal recommendations for such objects in Cygnus.


For LAAS members, Cygnus has a lot going for it. For starters, it passes directly overhead for LAAS members, or it will if the date and time are right. For another, the three classes of objects that are the easiest to image, Globular and Open clusters, and Planetary nebula, are found near the Milky Way, which passes right through the constellation. The reason why these three types of objects are easier to image has to do with what they’re made of. Stars are probably the easiest objects to image, so clusters tend to be easy objects. Planetary nebula have a high surface brightness per square arc-second, compared to more nebulous objects like galaxies and emission nebula.


To generate the list, I used the observing list generator on the NGC/IC project list. This website is the result of the research project dedicated to correcting the NGC and IC lists from the mistakes it contains. Its address is:
http://www.ngcicproject.org/.


I then used the STScI DSS images through the website at
http://archive.stsci.edu/cgi-bin/dss_form
to determine which ones might be worth the effort to photograph.


Now granted, photographs lie. Film does not respond to light the way the human eye does, particularly at low light levels. It’s the same with CCD sensors. They act linearly to light, so one photon, one count. But the human eye responds logarithmically, so at low light levels your eyes are more sensitive to light, while at bright levels the sensitivity drops off. This is why your eye can see both Jupiter and its moons through a telescope with ease, but your web camera can only see the moons if you over-expose Jupiter, or sees them with less contrast. So the DSS photographs do NOT show what your eye might see. Another reason those photos lie is that they’re black and white, so any colors in the stars are gone.


Nevertheless, the DSS images do give you some idea of the variations in brightness of the stars, the relative brightness of the object, and how large the object is.


The list that follows are my personal choices. Depending on how you deal with light pollution, they should made good visual as well as photographic objects. I give this as an example of how you can use Internet sources to generate lists of object, and how to determine which ones are worth looking at. And star clusters and planetary nebula tend to be easier to see from urban locations than other objects, so I urge visual observers to give these a try.


Now, this is not the complete list of all open clusters in Cygnus. Many didn’t look too photogenic to be worth the effort for my camera, with a field-of-view of 18 arc-minutes on the horizontal, 14 arc minutes vertical. Also, I’m skeptical of the magnitude estimates. But in the case of opens, I suspect they’re either the brightness of the brightest star, or more likely the average brightness of the individual stars.


By the way, diffraction spikes around stars gives a certain artistic touch, and for those telescopes like SCTs that don’t have one, they’re easy to produce. Simply tape two thick threads across the front of your tube, but DO NOT put tape directly ON your front lens!! Put the threads at right angles to each other, and you have diffraction spikes !

All images have north up, east to the left, and are 18 arc-minutes wide by 14 arc-minutes high. The data from the NGC/IC project is just below each image.

image001

Object   RA ----(J2000)---- DEC Obj Phot Vis Sfc Obj    Other
Desig.   H M S      Deg  ’ ”    Typ Mag  Mag Brt Size   Desig.
--------------------------------------------------------------------------
NGC 6819 19 41 18.0 +40 11 12   OC  7.3  7.3 ---- 5'   Cr 403


This one caught my eye because it seems to look like a cup with the open end up. Much like the game link-up-the-dots, part of the charm with open clusters are the shapes the stars can take. I’m doubtful about the magnitude estimate of 7. DSS images tend to be taken at about the same exposure level, so I suspect the estimate is of the brightest stars in the cluster. Still, this cluster shouldn’t be too difficult to catch. And remember, one great thing about clusters are the sometimes contrasting star colors. Take a chance and see what you can see !

image002

Object   RA ----(J2000)---- DEC Obj Phot Vis Sfc Obj  Other
Desig.   H M S        Deg ’ ”   Typ Mag  Mag Brt Size Desig.
--------------------------------------------------------------------------
NGC 6871 20 05 59.3  +35 46 38  OC  5.2  5.2 ---- 30' Cr 413


Given the large size of this open, obviously this image doesn’t capture all of it, but the arrangement of stars is wonderful ! Note the oval of tightly spaced stars around the central two bright stars, and the angle of tightly spaced stars around the two bright stars below and to the left of the central ones. There are other shapes created by closely spaced stars all across this part of the cluster. Now, whether all these stars are part of the cluster is moot. It’s the overall appearance that counts. As for the very faint nebulosity, it might be out of reach of visual observers, and in any case you’ll probably need very dark skies to even image them.

image003

Object  RA ----(J2000)---- DEC Obj Phot Vis Sfc Obj Other
Desig.  H M S       Deg ’ ”    Typ Mag Mag Brt Size Desig.
--------------------------------------------------------------------------
IC 1311 20 10 18.0 +41 13 00   OC  13.1 ---- ---- 9' Lund 928

 

As is usual for IC objects, this one is faint, but relatively dense. The two relatively bright stars should pin down the location. The shape, to me, vaguely resembles the Wild Duck open, M-11, much farther south in Scutum, but only a look will tell. Again, the very faint nebulosity is probably a target for large telescopes under very dark skies.

image004

Object   RA ----(J2000)---- DEC Obj Phot Vis Sfc Obj Other
Desig.   H M S      Deg ’ ”     Typ Mag Mag Brt Size Desig.
--------------------------------------------------------------------------
NGC 6910 20 23 12.0 +40 46 43   OC  7.4 7.4 ---- 7' Cr 420


I doubt it would be possible to photograph, let alone see, the faint nebulosity surrounding this open, but the combination of the few relatively bright stars with the mixture of fainter ones makes this open a possible beauty.

image005


Object   RA ----(J2000)---- DEC Obj Phot Vis Sfc Obj Other
Desig.   H M S       Deg ’ ”    Typ Mag Mag Brt Size Desig.
--------------------------------------------------------------------------
NGC 7031 21 07 12.5 +50 52 32   OC  9.1 9.1 ---- 5' Cr 430


Sparse, but a potentially very pretty and little-known open.

image006

Object RA ----(J2000)---- DEC Obj Phot Vis Sfc Obj  Other
Desig.   H M S      Deg ’ ”   Typ Mag  Mag Brt Size Desig.
--------------------------------------------------------------------------
NGC 7044 21 13 09.3 +42 29 46 OC 12.0 12.0 ---- 3.5' Lund 984


This one, although faint and small, drew my attention due to the many lines of stars running here and there.

image007

Object   RA ----(J2000)---- DEC Obj Phot Vis Sfc Obj Other
Desig.   H M S       Deg ’ ”    Typ Mag Mag Brt Size Desig.
--------------------------------------------------------------------------
NGC 7128 21 43 57.7 +53 42 55   OC  9.7 9.7 ---- 3.1' Cr 440

 

This tight, dense open might be a bit on the faint side at magnitude +9, but it should photograph well.

image008

Object  RA ----(J2000)---- DEC Obj Phot Vis Sfc Obj Other
Desig.  H M S      Deg ’ ”     Typ Mag Mag Brt Size Desig.
--------------------------------------------------------------------------
IC 5146 21 53 24.0 +47 16 00   OC  7.2 ---- ---- 9' Lund 1001


When I called up this image, I was surprised. The IC catalog lists this object as an open, but does not list the nebula ! A comparison of this red light image with the blue light image shows that this nebula is primarily red in color. This means it is relatively faint to the eye, because the eye is not sensitive to red light. It resembles the Trifid nebula, M-20, away far south in the Dixieland of Sagittarius. It happens that this nebula lies at the “head” of the dark nebula complex known as the Cocoon nebula.
So try these on your next visit to Cygnus, urban or dark sky. And please let me know what you find !

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