Pushing the limits at ESP'11

This past week I attended the Eldorado Star Party, held at the X-Bar Ranch near Eldorado Texas. This is an annual star party hosted by the Austin and San Antonio astronomy clubs.  This is my second time attending this event and it is quickly becoming one of my favorite star parties.

There are two real positives that this star party has. First, and foremost, the weather is almost always very good. I was able to observe four of the five nights I was there and with near perfect seeing and transparency. Second, the skies are really dark. There is a small light dome from Sonora in the south and Eldorado in the North-East, but neither is more than 20 degrees above the horizon. So dark skies and great weather make a perfect combination for a star party.

The party was well attended this year. I arrived on Monday and found a spot on the West side of the field. I set up beside some folks from the Central Texas Astronomical Society. These folks proved to be real friendly and I enjoyed their company throughout the week.

By Friday, I estimated that there were 175 people on the field. While the field seemed "full" it was not overly crowded.

Monday through Wednesday proved to be pretty good skies allowing me to log in excess of 20 objects a night, peaking at 26 objects on Wednesday night. Clouds finally rolled in after midnight on Thursday morning and with the clouds came a cold front. Temperatures went from the 70's to the 40's and cold weather gear was the order for the day. Thursday was spent  at the Ranch House avoiding the cold and catching up on my observation logs. Thursday night looked to be a washout and so I joined the others at the Ranch house to watch the Rangers give away the World Series to the Cardinals in Game Six.  Friday night proved to be the best of the lot, The cold front had moved out any moisture in the air and the skies were clear and crisp.  I logged another twenty plus objects on my Herschel 400 list. This was my last night at the party. By 10AM Saturday morning I was packed up and heading East down I-10 towards home.

So, why the title "Pushing the Limits?" Well, this year's observation list was entitled, "Peeling the Onion." The idea was that there was a list of lesser well known objects within close proximity to a very well known object. For example, M31, the Andromeda Galaxy was on the list as well as its companion galaxies M32 and M110. Easy right? Anyone that has a half-way reasonable telescope has seen these. Well how about NGC 206 or some of M31's globular clusters? Not so easy now. Some of these objects are listed at magnitude 14. Until now, I had never even attempted something that faint. This was going to "push the limits" of my scope.
Last year at ESP'10, my Zhumell 10" was brand spanking new and I was content with seeing how it performed on some easy-to-find galaxies. While the dark skies of this year's Texas Star Party would have provided an excellent opportunity to "go deep" and see what the scope could really do, the weather did not cooperate. So, this week I had the weather and the dark skies in my favor. If the 10" water heater was going to prove its worth, it was going to be this week. It did not disappoint me. Armed with a good star map, courtesy of Sky Tools, I went in search of M31's globulars. Boy these guys are faint, but I did see them with averted vision. Equally as tough was some of the star clouds in the Pinwheel galaxy. I got so carried away with looking for these guys that I ended up observing two or three additional ones that were not even on the list!

So, I muddled my way through the list and achieve my pin before the clouds rolled in on the Wednesday night. Objective 1 out of the way, but there was still the H400 list that I was working on and a series of Galaxy Clusters that I wanted to observe as this is one of the few sites dark enough that I would have a chance at.


One of the clusters that I have been wanting to observe is a chain of five galaxies in Pegasus that are known as Stephen's Quintet. I notice as I was observing NGC 7331 off of my H400 list, according to my star chart, Stephen's Quintet was about a degree to the North-East of this galaxy. So, I gave it a try. The first thing you notice when you spot these guys are their stellar-like cores. As you stare into the eyepiece and concentrate more, slowly the ghost-like halos start to emerge. They are still very faint, but noticeable. The two galaxies in the center NGC 7318A and 7318B are so close together that they appear as one single object. The fainest of the five is NGC 7317 which comes in at 14.6 magnitude!

By far, Stephen's Quintet was the best site of the week. The 10" Zhumell, "Zoe" has once again impressed me. Aperture rules!

Clear skies
rw

Globular Clusters

This week I've decided to share some thoughts and observations on globular clusters. For those non-astronomy folks that might be following this blog, globular clusters, or "globs,"  are a group of stars that are bound tightly by gravity into a ball or "globe" like structure. They are generally more dense at the center with the density falling off as you move away from the core.
The spectral analysis of the stars of globular clusters show very little evidence of metals. What this means is that the stars are extremely old. The origins of these clusters is not well understood. What is known is that most galaxies do seem to have these structures in their halo regions. Our Milky Way galaxy is home to about 150 globs. Large galaxies at the center of galaxy clusters can have many thousands of these globs. It is probable that these clusters are artifacts from interactions between a large galaxy and dwarf galaxies where the larger galaxy strips away the outer stars from the dwarf galaxy leaving only the core to be locked in orbit around the larger galaxy. Evidence that supports this theory has been found in the form of super-massive black holes that live in the center of these globs. This seems to indicate that these structures were once galactic in nature.

Globs make a good targets for urban observers as the are generally pretty bright. The majority of globs have apparent magnitudes less than 9. Globs are classified by the compactness of their structure. The Shapely scale rates globs on a scale of I to XII with I being the most concentrated and XII being very loose.  Things to note while observing globs are, a) degree of compactness, b) color and brightness differences of the stars, c) resolution of stars in the central region, and d) the presence of dark lines or trails of stars.

Below are some images of globs that I have observed over the last year or so. The images are all from the Sloan DSS survey. They are all 60X60 arc minutes which makes them appear 50X bigger than they are to the naked eye.

M4 - Scorpio

Discovered in 1746 by Cheseaux, M4 is a magnitude 5.8 globular in Scorpio. It is about 6,500 lights years distant from us, making it one of the closest globulars to us. It is relatively easy to find, being within 1.5 degrees of Antares. It is somewhat loose compared to some of the other globs. It is a Class IX on the Shapely scale.

Aug 21, 2011 - Backyard
Zhumell 10" f/4.9

Smart Astronomy 12.5mm, 100x
Nice loose globular, stars resolved down into the core, streamers of stars trail off to the south of the cluster. 

M5 - Serpens Caput

M13-Hercules

M5 is a Class 5 globular in Serpens Caput. It spans 165 light years in diameter and as such is one of the largest globs in our galaxy. It is 24,500 light years away.


May 10, 2010 - Texas Star Party
Orion 8" f/4.9 
Smart Astronomy EF 16, 62x

Very nice globular. Stars resolved clearly, central regions are mottled.










M13 is one of the most beautiful globs in the sky. It is one of two globs which Messier cataloged in Hercules, the other being M92. It is about 21,000 light years distant, which is relatively close. It is above average in both brightness and luminosity. It is a Class 5 on the Shapely scale.

M71-Sagitta

M15 - Pegasus

June 16, 2010 - Bar-X Ranch
Orion 8" f/4.9
Gorgous globular. Concentration increases towards the center. Stars resolvable to the core area. Concentrations of stars radiate outwards in arm-like protrusions. 






M71 is a very loose glob in Sagitta. It is situated in a very rich star field which exaggerates its lack of compactness. Nevertheless, it is a Class X glob. M71 also has the distinction of having stars with elevated levels of metals, meaning that it may be a lot younger than most of our galaxies globs. It is 12,000 light years away

November 4, 2010 - Eldorado Star Party
Zhumell 10" f/4.9
Sirus Plossl 9mm, 139x 
GC Nebula in Sagita. Rich field stars.  









M15 is a Class IV glob about 33,000 light years from us. It has the distinction of being the first glob to have its super-massive black hole detected, thus adding evidence to the theory that globs were once a type of Dwarf galaxy.



(not observed as of posting)

Omega Centaurus

Omega Centari is unlike other globs as it was given its name as if it were a star. This is a result of this glob being bright enough that it appears stellar to the naked eye. It is a Class VIII glob which is 15,600 light years distant. It is our galaxy's brightest glob with a luminosity of 1.1 million suns.

May 12, 2010 - Bar X Ranch
Orion 8" f/4.9

Smart Astronomy EF 16, 62x 
Omega Centaurie is an amazing globular cluster. Stars are resolvable to the very core of the cluster. Many dark lanes are also present






Next time out, put a few of these globs , or other ones, on your target list. I assure you that you will not be disappointed.

Clear skies;
rw

Sketching

Over the years of observing, I have often taken the opportunity to sketch the object that I am observing. One of the things that sketching does is it makes you slow down and spend time to search out the details of the object. Sketching also gives you a visual record that goes beyond your notes, and if you can operate a scanner it allows you to share your eyepiece experience.

Recently, I finally figured out how to operate my scanner on my multi-use printer. So, I scanned in a few sketches that I made at last year's Eldorado Star Party  and then did some adjustments with Photoshop. The sketches are done with graphite pencils on a white sketching paper. The scanned images were cropped, adjusted for brightness and contrast and then inverted so it would turn it into a white on black background. I also touched up the individual stars a bit to make them look a bit more round.

So below are a few examples of some of my sketches I did at last year's Eldorado Star party. 

NGC 1035, 1042 and 1052 are a trio of galaxies in Cetus. This is a nice tight grouping that fits into the field of view of my 16mm eyepiece (46 arc min). NGC 1042 is face on spiral and very soft visually. 1052 is an edge on spiral with the hint of a visible core. 1035 is another edge on galaxy but with even brightness along its length.

NGC908 is a SABc spiral galaxy in Cetus.  The spiral is at an intermediate angle. The core is visible and is approximately 3 arc min long.

NGC 253 is known as the Sculptor Galaxy. It is relatively bright at 7.9 mag.  This is another spiral SABc galaxy which is viewed nearly edge on. The core is very visible and well defined.  Charles Messier missed this object and its discovery in 1783 is credited to Caroline Herschel, sister of famous deep sky observer William Herschel. 

So the ability to digitize my sketches and share them has increased my interest in this aspect of the hobby. Going forward my plan will be to do more sketches. More to come....

Clear skies;

rw