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

Degree Circles - the poor man's goto

Those that know me realize that I am quite judicious with how I spend my money. My family might even call me "cheap." Nevertheless I am always on the lookout on ways to enhance my hobby and especially when it comes with an attractive price, (read "cheap" here). So you know that I own a large dob. One of the disadvantages with Dob's is that it is rather difficult, and expensive, to equip them with one of those computer pointing devices we call "goto's."  Goto's have revolutionized our hobby by allowing relatively inexperienced celestial navigators find the treasures in the heavens.  Now I grew up in this hobby by star hopping my way to my targets and I would never recommend anything different for the novice as it forces the newbie to learn the sky. That being said, there is a place for goto's in the hobby. Goto's allow one to increase the speed at which objects are obtained allowing more time spent observing the object and coaxing out the subtle details which is only possible when one spends time observing it.

Now as I said, goto's for large dob's are expensive and you all know my penchant for conserving those green backs. Fortunately, there is an alternative for those, ahem, "cheapskates" like me. Enter the degree circles. Degree circles are a set of graduated circles that are positioned on the azimuth and altitude axis of the telescope. Together with some software, running on either on a laptop or an iPhone, they can allow the observer to point the scope at a set of coordinates for a specific object. The power for pointing the scope still comes from the observer and there is no tracking capability, but it does allow faster acquisition of the target and thus allows for more time at the eyepiece. All this for less than 50 bucks!

A few months ago I decided that I was going to perform this scope modification. The first thing I did was to read up on some experience of others who went before me. Why learn from your own mistakes when you can learn from those around you eh? A great place for this type of information is the Cloudy Nights forum. Here is a huge thread that has a lot of information on installing these degreecircles.

In this thread, I found several PDF files for various diameter azimuth circles. My 10 inch dob has a 22 inch diameter base board, so I needed a 22 inch diameter circle. I found a PDF file for the appropriate size, and took the file on a flash drive to my local Office Max to get it printed out and laminated. The printing was "cheap" at about 4 dollars. The laminating was even cheaper, free in fact, because I had to show the clerk how to reload the stock and set up the machine.


Once home, I cut out the circle and placed it on my base board, making sure any excess was trimmed off.  I then needed to cut out the inside of the circle. I fixed the circle onto the baseboard with some all purpose duct tape.

You can see the azimuth circle attached to the base of the scope in the picture to the left. The white circle in the center is the "Lazy Susan" azimuth roller bearings.

Now for the tricky part. I say tricky because when ever I take a jig saw to a precision instrument like a telescope, I get a bit nervous. Because the base that the scope is attached to is of the same diameter as the bottom board, you must remove a portion of the base so you can see the degree circle. So, I used a jigsaw to cut out a 3" by 1" notch. This allows me to see about 15 degrees of the degree circle. I placed this cutout at the front of the scope, directly below the handle. This allows me to see the bearing while still seated at the eyepiece. I painted the newly exposed surface so the particle board would not suffer an ill affects due to moisture.


So, I am almost complete on the azimuth circle. All I need now is an adjustable pointer. Why adjustable? Well, it needs to be adjustable so that you can get it aligned properly. I will talk more about this in a minute. I affixed a magnet to the base board with some double sided tape. I then fashioned a pointer from some scrap wire. I now have a movable pointer on the azimuth axis.  Now I also took the opportunity to affix a bubble level to the base board using the double sided tape. This level comes in handy when setting up the scope at an observation site as the scope needs to be perfectly level to maximize the pointing accuracy.

Now onto the altitude degree circle. I could have done something similar and printed out a degree circle for the altitude bearing but there is a simpler method. I went to my local hardware store, Lowe's, and found what they call an "Altitude Meter." This is degree circle with a weighted needle. It gives the angle from the vertical. Now astronomical altitude measurements are given as the angle from the horizontal, but using my grade school geometry, I can simply subtract the altitude bearing from 90 to get what the indicator on the altitude meter should read when I am on the object. The best things about the altitude meter is that it has a magnet which allows it to be placed and removed from the optical tube easily and was only about 20 bucks.


So now it is complete. When I take it out to my observing site, I first use the compass app on my iPhone to get a rough alignment of the bottom baseboard to North, or 0 degrees. I then make sure it is level using the bubble level. If it is off, I shim up the feet until it is level. I then point the scope to a bright star whose alt/az position I know from a real time running software like Stellarium or my beloved SkyTools3. If the scope is level, then the altitude should be dead on. I just need to move my adjustable pointer to the  azimuth that the software is calling out for that particular star. And that is it. I can read the alt/az for any object from the Stellarium or SkyTools3 and push my scope to those bearings and presto, there's the object in the wide field lens. Its like shooting fish in a barrel! It is almost like cheat'n.

Clear skies;
rw