[LVAS] October Observer's Challenge - NGC-253

[Fred Rayworth]

MONTHLY OBSERVER’S CHALLENGE
Las Vegas Astronomical Society
 
Compiled by:
Roger Ivester, Boiling Springs, North Carolina
&
Fred Rayworth, Las Vegas, Nevada
 
October 2009
NGC-253 (The Sculptor Galaxy)
 
Introduction
The purpose of the observer’s challenge is to encourage the pursuit of visual observing.  It is open to everyone that is interested, and if you are able to contribute notes, drawings, or photographs, we will be happy to include them in our monthly summary.  Observing is not only a pleasure, but an art.  With the main focus of amateur astronomy on astrophotography, many times people tend to forget how it was in the days before cameras, clock drives, and GOTO.  Astronomy depended on what was seen through the eyepiece.  Not only did it satisfy an innate curiosity, but it allowed the first astronomers to discover the beauty and the wonderment of the night sky.
Before photography, all observations depended on what the astronomer saw in the eyepiece, and how they recorded their observations.  This was done through notes and drawings and that is the tradition we are stressing in the observers challenge.  By combining our visual observations with our drawings, and sometimes, astrophotography (from those with the equipment and talent to do so), we get a unique understanding of what it is like to look through an eyepiece, and to see what is really there.  The hope is that you will read through these notes and become inspired to take more time at the eyepiece studying each object, and looking for those subtle details that you might never have noticed before.  Each new discovery increases one’s appreciation of the skies above us.  It is our firm belief that careful observing can improve your visual acuity to a much higher level that just might allow you to add inches to your telescope.  Please consider this at your next observing session, as you can learn to make details jump out.  It is also a thrill to point out details a new observer wouldn’t even know to look for in that very faint galaxy, star cluster, nebula, or planet.
NGC-253
            NGC-253, known as the Sculptor Galaxy or in some circles as the Silver Coin Galaxy, is a bright and easy to see object in the southern skies.  The further south one is, the better it appears.  However, it has been seen at most latitudes within the continental U.S.  At approximately 7.1 magnitude, it has been spotted with the naked eye in far southern locations when conditions are right.  Discovered by Caroline Herschel in 1783, it has been a popular object ever since.
            The galaxy is known as a starburst galaxy because it has many active star forming regions within it.  Though these type galaxies are known for supernovae, only one has been discovered within this galaxy, and that was in 1940.
            It is full of a surprising amount of detail, from the lumpy central bulge, to the dark lane and several foreground stars.  It appears as a fat streak in smaller telescopes and in larger ones, the details emerge.  In X-ray images, a central bar is evident.  It is considered a great binocular object and is the most easily seen external galaxy next to the Andromeda galaxy.
Deep-Sky Wonders:  Walter Scott Houston; Selections and commentary by Stephen James O' Meara.  At 7th magnitude it is a spectacular object for visual observers and astro-photographers alike.  It is one of the 14 nebulae and clusters discovered by Caroline Herschel in England during her sweeps for comets in the years 1782-83.  Observing from the Cape of Good Hope a half century later, her nephew John Herschel described it's appearance in his 18.5-inch speculum-metal mirror:  "Very, very bright and large; a superb object... 24 arc minutes in length.  Its light is somewhat streaky, but I see no stars in it except 4 large and 1 very small one, and these seem not to belong to it, there being many near."
The galaxy was easily seen in Vermont with a 6-inch rich-field at about 20X.
How to Use an Astronomical Telescope:  James Muirden.  A galaxy visible as a nebulosity in the finder.  It is considerably elongated in a NE-SW direction, and has a star of about magnitude 9.5 on its NW edge.
1000+ The Amateur Astronomer's Field Guide to Deep-Sky Observing:  Tom Lorenzin.  7M; 25' x 4' extent; very bright and large; oblique view with axis oriented NE-SW; great binocular object; mottling visible at >200X; good supernova prospect; 1.75° SE is GLOB NGC-288.
The Finest Deep-Sky Objects:  James Mullaney and Wallace McCall.  NGC-253 looks somewhat like M-31 but smaller.  Though large and bright, it needs a first class night for a good view, due to its southerly declination.  Seen well in the 6-inch.
The 105 (+1) Finest Deep-Sky Objects Revisted:  Roger Ivester.  This edge-on spiral appears as a streak of light with mottling and a brighter middle.  It is approximately half a degree in length, with several bright stars superimposed.  Viewed with the 10-inch at 125X.
Observing Handbook and Catalogue Of Deep-Sky Objects:  Skiff and Luginbuhl.  This galaxy is easily visible in binoculars and a fine sight in any aperture.  With 6 cm it is a high surface brightness broadly concentrated spindle elongated NE-SW lying just N of two mag. 9 stars.  In 15 cm the halo can be traced out to 25' X 5' in pa 50°.  At least three stars are visible, superimposed on the nebula itself.  In 30 cm the galaxy is a huge, mottled glow showing hardly any overall concentration.  At 225X a dark band lies against the NW side of the core.  Other than the two bright stars off the S flank, about a dozen faint stars are intimately involved with the galaxy.
The Herschel Objects: Ancient City Astronomy Club.  Magnitude 7.1 spiral galaxy in Sculptor.  25.1' in size.  Extremely elongated, a band of light or streak across the eyepiece field.  Covering 30' across.  Bright in center, fading towards the outer rim.  Less than 1° from globular NGC-288 (8-inch Cass.).
Observations/Drawings/Photos
Roger Ivester (see Rogers Pictures 003.jpg):  Observer from North Carolina
He first observed NGC-253 many years ago.  It was the second object listed in one of his first deep-sky observing guides, The Finest Deep-Sky Objects by James Mullaney and Wallace McCall.  His observation notes and sketch for this month will be from a very special observing session in October of 1995 using a 14.5-inch reflector.  At 125X this galaxy measured almost a full 1/2° in length.  The texture showed much mottling with little concentration especially in the outer halo extensions.  With careful observation there was a small and very subtle core which was difficult to see.  The orientation of this galaxy was NE-SW.  There were two magnitude 9 stars situated just off the SSE part of the halo.  He could see four faint stars superposed or embedded within the nebula (see Rogers NGC 253.jpg).
Due to this galaxy’s sky position which is low in the southern sky at -25° S latitude in North Carolina, a night of excellent transparency and seeing is required to see the true majesty of this incredible object.
Fred Rayworth (see Fred At Death Valley.jpg):  Observer from Nevada
            He has observed this galaxy many times over the years and never gets tired of it.  At Death Valley, he gave his most elaborate description of this showpiece.
            The first time he tried for it, it was too low and just over the aircraft hangar next to where they had set up.  However an hour later it was high enough in the sky for an attempt.  Unfortunately, the stars were not very bright at that altitude and he had to hunt and peck before he finally found it.  The one thing about this galaxy is that if one gets in the general area, there is no doubt when the scope sweeps over it!
            At 70X, it fit nicely into the field of view, but at 140X, it went beyond it. He swept both ways at 140X to see how far the halo extended and it cut off abruptly a little beyond the field.  The galaxy was a fat elongated oval, with plenty of lumpiness in the core and several bright stars, plus some fainter ones, embedded within it.
            He noticed a dark lane, of sorts, with the main nebulosity above it.  Not quite like the Sombrero, but similar.  There was a lot of lumpiness within the core which extended over 60% of the field.  At 140X, a bit of spiral structure was just hinted at in the central area.  He never saw the bar shape, though he saw hints of it with the dark and light shaded areas giving a vague impression of some shape.  There were also several stars superimposed in front of it. The brighter ones combined to form a pseudo-W similar to Cassiopeia. He didn’t realize the shape at the time, but saw Jonathan Kade’s notes and the description just clicked.  He gives full credit for Jonathan pointing this out (see Freds NGC 253 Unfiltered.jpg).
            As a final experiment, and against what he usually tells newbies, he put on his O-3 filter to see if he could suss out any knots (at 140X).  What he got was 60% of the core which still extended almost to the edges of the field.  However, the fuzz in the arms was gone as well as most of the foreground stars.  As hard as he tried, he could not see any specific knots, though he saw a bit of lumpiness (especially in the center) that looked a bit different from the unfiltered view (see Freds NGC 253 Filtered.jpg).
            Overall, this is one of his favorite objects and is sure to be on his list again the next time he goes out.  Maybe from Redstone Picnic Area at Lake Mead, it will be a bit higher in the sky.
Rob Lambert:  Observer from Nevada
The Sculptor Galaxy is his favorite galaxy.  He was completely enthralled the first time he observed it.  Unfortunately, that was before he started keeping notes.  This galaxy has more detail in its structure than one will see in most galaxies.
The first time he observed the Sculptor Galaxy was last winter in Rio Rancho, New Mexico.  It was extremely cold that night, but he must have gazed at this treasure for at least 20 minutes.  He could just imagine the churning gas and dust within its spiral arms.  This first image (Nov 2008) was taken that night almost a year ago when the sky was so dark and steady on the outskirts of Albuquerque that he was able to capture it with only a 14-second integration.  It is a single frame image with no post processing of any kind (see Robs NGC 253 LX200 14 Sec.jpg).  The second image (also a 14-second exposure), captured recently with the Orion ST120, provides the perspective that probably gives the Sculptor Galaxy its other nickname, the Silver Coin Galaxy.  As one looks at the smaller image of the galaxy, one can almost imagine a coin being suspended in space (see Robs NGC 253 ST120 14 Sec.jpg).  He tried to capture a 56-second image while at Death Valley to show more detail in the galaxy's center, but the transparency wasn't very good for that much magnification (see Robs NGC 253 56 Sec.jpg)
There are obvious dark globs and streams of dust throughout entire length of the galaxy.  Its core and nuclear bulge are tighter, more distinct, and less washed out than that of most galaxies.  When he’s seen IR or X-ray images of the Milky Way's center, he’s imagined it looking something like NGC 253.  The dust lanes on the north side remind him of the dust lanes visible in the much larger Andromeda Galaxy, as they spiral in toward the galaxy's center.  As he looked to define the galaxy's spiral structure, he saw two large spiral arms that appear to originate at opposite ends of a short bar stretching across the galaxy's center.  If he orients the images correctly, the spiral arms give the galaxy the appearance of a clockwise rotation.  What he would give to look directly down upon this galaxy and observe its full spiral structure!  The brighter foreground stars that are superimposed on the galaxy appear to be riding the spiral waves as the galaxy revolves around its center.  There are a number of areas of apparent star formation, but between the core and the bright star on the northeast periphery there is what seems to be an unusually bright area of star formation.  According to published documentation, NGC 253 is a starburst galaxy similar to M82.
He looks forward to years of observing this galaxy and trying to see something new each time.  NGC 253 will long be a fall and winter favorite of his.
Jonathan Kade:  Observer from Detroit, Michigan
Fantastic object for this month!  He’s never seen this amazing galaxy before - and somewhat surprisingly to him, neither had most of the people on the field at his club's star party this weekend, 17 October, 2009.  The general consensus was that C65 had to be one of the best objects that they'd never seen before.
At only about 20 degrees over the southern horizon, though, it's somewhat easy to excuse the omission.  They're used to having the southern sky washed out to 30 degrees at their observatory north of the Detroit metropolitan area.  The watery constellations are a fairly star-poor area of the sky anyway, but even in black skies without optical aid, there was simply nothing there aside from a few scattered fifth magnitude stars below Deneb Kaitos.
With lots of scintillation near the horizon, Sculptor didn't seem like a promising region of the sky on Saturday night.  However, once transit time neared for C65, he decided to have a look with binoculars.  He got out his Pocket Sky Atlas, and looked at the various maps of Sculptor for some context.  He noted that “To be honest, it took a little guesswork to pick out Beta Ceti, as Cetus is almost always awful near home.”  Fomalhaut helped him get his bearings, though, and he was off.
He turned his wife's 15X70 binoculars to Beta Ceti (after melting the frost off their objectives), and scanned down toward the horizon.  And right away, there it was.  The lumpiness and asymmetry reminded him a lot of M106 - but that was through an 8" reflector!  He was very excited now to see it with his telescope.  The 2" 25mm eyepiece showed off the extent of the galaxy marvelously.  He hadn't realized before just how large or how bright this object really was.  With the Webster Astronomical Society's 22" Dob on the field and between targets (after giving up again on the Bubble Nebula), he had to see it with more aperture.
With a 40mm Pentax EP providing a FOV just large enough to hold the whole galaxy, the object looked almost three-dimensional enough to touch.  The arms were still somewhat tough to identify, but he did have some impression of two arms with a bar.  The dust lanes and patches, though, really stood out, and helped greatly with identifying the orientation and "sense" of the galaxy.  Then he started asking others if they were familiar with this galaxy.  Many were not, and pretty soon almost everyone who wasn't actively imaging was standing around the big scope.  This object was the defining one of the star party.
While others were observing, he ran inside and got out the sketching pad.  (It was 20 degrees Fahrenheit, so he'd been somewhat neglectful of his note taking.)  He wrote his initial impressions along with a sketch from visual memory.  Then he went out to spend some more time with the object (see Jonathans NGC 253 Notes.jpg and Jonathans NGC 253 Drawing.jpg).
Viewing the galaxy again after returning outside, he noticed the foreground stars much more keenly.  The psuedo-Cassiopeia asterism was amusing, and made him think of the galaxy's similarities to (and differences from) M31 a bit.  The triangle of stars overlaid on the bulge was an interesting sight as well.
He wishes he'd spent more time on the nucleus at high powers, but eventually they had to move onto other objects with the big scope.  The Silver Coin will definitely be a staple of fall star parties for many years to come, though!
His final thought was “Thanks very much for choosing this amazing galaxy.  This is one southern object that northern observers shouldn't be missing!”
References
(Submitted by Roger Ivester)
Deep-Sky Wonders:  Walter Scott Houston; Selections and commentary by Stephen James O' Meara
How to Use an Astronomical Telescope:  James Muirden.
1000+ The Amateur Astronomer's Field Guide to Deep-Sky Observing:  Tom Lorenzin
The Finest Deep-Sky Objects:  James Mullaney and Wallace McCall
The 105 (+1) Finest Deep-Sky Objects Revisted:  Roger Ivester
Observing Handbook and Catalogue Of Deep-Sky Objects:  Skiff and Luginbuhl
The Herschel Objects:  Ancient City Astronomy Club
Sky and Telescope Magazine Deep-Sky Wonders by Walter Scott Houston, Selections and Commentary by Stephen James O’Meara, Sky Publishing Corporation, Cambridge Massachusetts 1999. 		 	   		  
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