The Keen (...or perhaps near-sighted) Archer of the Sky
From: firstname.lastname@example.org (Clay Sherrod)
In our eleventh Constellation Guide, "GO TO SAGITTARIUS" of the series "GO TO GUIDES for the ETX and LX 90 Telescope Users" we are penetrating the very core of our Milky Way galaxy of over 200 billion suns. We are looking deep into the very nuclear center of the galaxy, through dense and rich star clouds, heavy concentrations of dark light-obscuring nebulae, and many wonders of deep space. As we approach this center, the density of the stars per parsec increases and the population figures become staggering. It is through this rich stellar field that we should take time to spend time, scanning slowly with our eyes, binocular, and our telescopes at the magnificent wonders that only this vantage point - Earth - has to offer.
It is worth your time and efforts to find yourself a "rock" somewhere in the secluded darkness of a moonless night and allow your mind to rest and wander as your eyes become more and more adapted to the subtle contrasts of a night only illuminated by the soft glow of the stars within our Milky Way; soon, multitudes of the most minute of images begin to emerge in your sight and in you mind as the brilliant Sagittarius Star Cloud takes shape and form. Soon....it is like watching the sunlight reflect from the sparkling grains of sand on the cleanest of beaches.
To many, the familiar brigher stars of Sagittarius outline what is commonly referred to as the "teapot," which can be quickly seen in my outlined diagram below which compares it to the traditional constellation pattern of the "celestial archer." The brighter stars (see the list below under "Object 1, Nunki") outline a perfect traditional teapot, complete with a pointed lid, spout and handle!
This area of the sky is so rich with clusters of stars ("galactic" or "open star" clusters), bright diffuse nebulae from which stars are actually "born," dark dust that blocks light and energy form the galaxy's core, hundreds of globular clusters.....and infinitely more.....that it boggles the imagination even to begin our TOUR. With so many objects to observe, most of them beautiful beyond belief, how do you choose which to spend your time on? Answer: do not choose, observe them all....they will be there for a lifetime!
So....this "GO TO" TOUR of Sagittarius, the great (or perhaps not-so-great) celestial archer, will be somewhat different than previous tours....we will have be a very short introduction into the overall history and views of this magnificent star field, and then we will concentrate exclusively on DEEP SKY objects for this TOUR - no doubles, no variable....just interesting DEEP SKY objects. Sagittarius is PACKED with them and I have been able to whittle down my list to only the 20 finest or most unusual objects. As you can see from the Arkansas Sky Observatory Constellation Chart above, there is a very high concentration of objects for us to view....but this is only the best objects. For every ONE that I have listed are hundreds of NGC, Caldwell, named objects, double stars, tremendous variable stars, dark nebulae and on and on.... Your AutoStar directory has many such NGC objects listed....double and multiple stars as well!
Note from the sky chart included here that the ECLIPTIC passes through the northern portions of Sagittarius; hence this is one of the twelve ZODIACAL constellations in that the planets, moon, sun and earth appear to move centered on the defining "middle point" that we call the "ecliptic." This is NOT to be confused with the CELESTIAL EQUATOR which passes far to the north of Sagittarius. That line is the reading "0" degrees on your properly adjusted declination setting circle. All angles NORTH of this equatorial line are positive ("+") and all angular measures (declinations) south of the celestial equator are negative ("-"); hence you will see references in this "GO TO" GUIDE to both "+" and "-" declinations for celestial objects.
Hence, even the HIGHEST OBJECTS in Sagittarius appear very low in the southern skies for northern hemisphere observers.....and ideally situated for our friends south of the Earth's equator.
Each GO TO object is discussed for your telescope regarding the type of conditions necessary for you to view it optimally for discern the very faintest details....double star challenges for each size telescope .....magnifications and aperture necessary for most objects, and much, much more. This is YOUR complete GUIDE to get you on your way to exploring this large and interesting constellation. Although there are MANY wonderful and colorful double and multiple stars that should be examined in your scopes, I have limited this "GO TO" TOUR to only deep sky objects. So, to find the names and locations of the best double stars, consult a good handbook, such as the "Burnham's Celestial Handbook," Vol. 3 for a very comprehensive list of locations, magnitudes and angular separations of these wonderful stars. There are many stars for EVERY telescope size and type.
Use this attached star chart and the following Guide as an excellent reference for your next star party itinerary, or a beginning for further study into the thousands of objects visible in this part of the sky. Truly these extensive Constellation Study Guides will most definitely put your AutoStar to work for you in the most efficient and enjoyable way possible! As a matter of fact, MANY AutoStar users are now programming their own "Tours" based on these guides, using each constellation as a separate GO TO Tour for the AutoStar library that can be added in or deleted through the main edit screen on your PC or MAC computer. Soon, you will be able to download EACH CONSTELLATION TOUR here on the Mighty ETX site custom-designed just for your AutoStar!
Already, there are TWO such tours that have been custom designed by ETX-user and contributor JIM MCCAMBRIDGE who has put together wonderful AutoStar programmable tours (to add to your library for AutoStar!) for Leo and Bootes, these based on my "GO TO" TOURS appearing on the Mighty ETX Web Site. You may copy these to file from: http://www.weasner.com/etx/autostar/as_tours.html and then "drag and drop" onto the Tours button of your AutoStar updater edit screen to include in the library on your PC.
We hope you enjoy these comprehensive GUIDES to touring the constellations via your AutoStar and its computer-driven telescope. Each new installment is complete with diagrams, charts and illustrations that you will find nowhere else. Please let us hear YOUR feedback and your observations of each and every constellation after YOU have toured its vast reaches of our skies!
In many cultural tales of old, the great archer Sagittarius is pursuing the huge Scorpion (Scorpius) who struck the fatal sting to the exposed foot of the great hero Orion and thus ended his seemingly never-ending ability at immortality. But in other tales, the archer clearly missed his target, as we see the arrow (the constellation "Sagitta" clearly gone astray, well above Aquila the eagle....in the opposite direction!
This is the ninth constellation of the Zodiac, following Scorpius and preceeding Capricornus. The mythological image of Sagittarius is that of a Centaur, apparently somewhat in conflict with our modern southern hemisphere constellation of Centaurus....who obviously is: also a Centaur!
It has long been speculated that there would be at LEAST twice as many Messier objects if Charles Messier had been observing and recording his "faint fuzzies" much further south in latitude than his homeland of France. Of the hundreds of naked eye and binocular objects throughout the Sagittarius Milky Way that are literally wonders to behold, he noted only 16 objects in this constellation, clearly as a result of atmospheric extinction to the south. "Atmospheric Extinction" is merely dimming of celestial objects as their light passes through the dense "lens" of air which increases in thickness as we level out near each horizon.
You will clearly see as you TOUR through this constellation that there are MANY MORE THAN 16 remarkable objects that you pass as you GO TO this guide's selected objects.....many objects that are seemingly ignored simply because they do not have that "Messier blessing...." Most are referred to in the NGC list (New General Catalog) and can be found in a good star atlas or reference list, and nearly all - once identified properly - are found by NGC number on your Autostar under "Select/Object/Deep Sky/NGC.....[scroll through list]." Many such objects can be found with the naked eye, or scanning with binoculars, very deep and low in Sagittarius.
YOUR SAGITTARIUS CONCISE DIRECTORY OF INTERESTING OBJECTS -
In Sagittarius are more objects visible in all scopes - from the wide field ETX 60 and 70 models, to the light-grabbing LX 90 - than you could possibly see in a lifetime. Interestingly, these are NOT mundane objects, either as you might imagine could fill some otherwise "empty" pages of a constellation like....well, Aries, devoid of a wide range of interesting objects. It was very difficult to select (and limit) the number of objects for our "GO TO" TOUR. Only the best and in some cases, most challenging, objects are chosen for this brief tour.
I have chosen the finest 20 objects in this Sagittarius "GO TO" TOUR; as with all GUIDES, all objects listed below will be visible in all telescopes (some naked eye) from the ETX 60 through the LX 90; of course larger apertures may "show" an object a bit closer and "better," but frequently a wide field and low power view is more desirable than aperture. This is the case for MANY of these objects since we are looking directly into the very star-cloud-rich areas of our Milky Way galaxy. Indeed, I strongly encourage you to step away from the telescope often and scan the beautiful open skies and star fields with a good pair of 7 x 50 or 10 x 50 binoculars. You will be tempted to venture to your "dark sky site" for a full evening of laying back on a blanket and scanning the skies with a good star atlas, a red flashlight, and a dependable "observing buddy."
I have many times just stood in awe for over several hours and peered at the beauty that is the space toward Sagittarius....you can never see this sight too often. Once your eyes are fully dark adapted, you will even be able to see The Great Sagittarius Star Cloud (see the wide-field photo below) appearing as its namesake a very open and bright cloudy object that is huge in the open sky, sprinkled with thousands of tiny naked eye stars. Even the binoculars will show dozens of deep sky objects that cannot be fully appreciated in large telescopes with limiting fields of view!
The darker adapted your eyes become....the more you will be able to see; in fact the Milky Way through Sagittarius has been know to even cast a shadow on the ground from observers in very dark skies!
You will note that this list of objects for Sagittarius is somewhat unique from other "GO TO" TOURS in that the objects are all grouped by category: 1) your "starter star", as always starting with a prominent star in the area to get you off and running; in this case it is the star "Nunki", or sigma Sagittarii; 2) prominent globular clusters; there are some wonderful globulars mixed among the dense star-rich skies of Sagittarius; we will START with a familiar globular (Messier 14) which we have examined in Ophiuchus (see http://www.weasner.com/etx/ref_guides/ophiuchus.html ) and proceed to check out all eight (8!) fine globulars in Sagittarius....Messier 14 will be your "marker" for comparison to the somewhat more difficult globulars in Sagittarius; and, 3) galactic star clusters and nebulae....so many clusters in this region have associated nebulosity with them that I have grouped this together!
For example,the fine star cluster Messier 18 is adjacent to the fabulous "Omega" nebula.....famous "Trifid Nebula" which can clearly be seen in our scopes is right next to the star cluster Messier 21!
Thus, for this "GO TO" TOUR guide for Sagittarius, we are breaking rank and NOT presenting the Messier objects in sequential numerical order as normally done.
As with all of the "GO TO" TOUR constellation lists, I recommend a good star atlas and/or chart which will list all the finest objects, constellation-by-constellation. One very handy reference guide is the PETERSON FIELD GUIDE TO THE STARS AND PLANETS, which features complete lists with declinations, right ascensions, magnitudes, and all pertinent information for you to expand your observing horizons beyond this brief GUIDE.
Note that your AutoStar will NOT have every object listed on every constellation GO TO tour....this is intentional. You can access some of the most interesting objects of the sky directly from their coordinates. It is quite simple as you merely enter these coordinates as follows in the 10-step process:
1) Press the "MODE" key and hold down for 3 seconds and release;
2) Displayed will be the current Right Ascension and Declination of the center of field of view of where your telescope is presently pointed (assuming that you have properly aligned from "home position");
3) [NOTE: if you have the Meade electric focuser attached to any of the ETX or LX telescopes, holding down the "MODE" key will bring up the "Focus" command first....merely scroll (lower right scroll key) down one step to access the RA and DEC to enter your desired coordinates]
4) Press the "GO TO" button on AutoStar;
5) This will change the display and you will note the cursor blinking over the first digit of RIGHT ASCENSION (R.A.); merely use the number keys and dial in the R.A. of the object you are searching for;
6) When done, press "Enter;"
7) This moves the blinking cursor over the "DEC" coordinates;
8) [NOTE: the declination, unlike R.A., can be either positive or negative and you will see the "+" or "-" sign displayed depending on where your telescope is aimed at that time; if it is NOT the desired setting (plus or minus), merely use your arrow key to move the blinking cursor OVER the "+" or "-" sign and change by using either of your lower corner SCROLL KEYS;
9) Proceed to enter the DEC using number keys;
10) Press either "Enter" or "Go To" when finished and the telescope begins slewing to your desired object!!
The constellation tour Star Chart above (click on and save to a file on your PC; then open it and re-size to fit the page and print for a very handy at-the-scope star chart) will get you started on your journey for this constellation.
Following is the concise object list for your "GO TO" TOUR of Sagittarius; you may wish to find the majority of the objects from the AutoStar Library (for example, you can easily go to the "Lagoon Nebular (Messier 8) " if you pull up "Object/Deep Sky/Messier Object/..type in '08'...." and then press "Enter", followed by "GO TO" to slew to one of the most beautiful bright nebulae in the entire sky. On the other hand, if you want to experiment and become a "better AutoStar user" try entering the exact R.A. and DEC coordinates of that object as described above after holding down the MODE key. You will find the accuracy of entered GO TO's to be somewhat less than those stored in AutoStar, but the capability of acquiring unlisted objects is fantastic!
OBJECT 1: bright star - NUNKI (sigma Sagittarii) - R.A. 18h 52m / DEC (-)26 22 - Magnitude 2.1 OBJECT 2: (reference starting object in Ophiuchus!) globular cluster - Messier 14 (ngc6402) - R.A. 17h 35m / DEC (-)03 13 - Magnitude 8.5 OBJECT 3: globular cluster - Messier 28 (ngc6626) - R.A. 18h 22m / DEC (-)24 54 - Magnitude 7.3 (nice!) OBJECT 4: globular cluster - Messier 22 (ngc6656) - R.A. 18h 33m / DEC (-)23 58 - Magnitude 5.9 (super one!) OBJECT 5: globular cluster - Messier 75 (ngc6864) - R.A. 29 03 / DEC (-)22 04 - Magnitude 8.0 OBJECT 6: globular cluster - Messier 55 (ngc6809) - R.A.19h 37m / DEC (-)31 03 - Magnitude 4.7! (but very low!) OBJECT 7: globular cluster - Messier 54 (ngc6715) - R.A.18h 52m/ DEC (-)30 32 - Magnitude 7.1 OBJECT 8: globular cluster - Messier 70 (ngc6681) - R.A. 18h 40m / DEC (-)32 21- Mag: 9.6 - tough one! small! OBJECT 9: globular cluster - Messier 69 (ngc6637) - R.A. 18h 28m / DEC (-)32 23 - Mag: 8.9 - not easy, very small! OBJECT 10: (in Scutum - FOR YOUR REFERENCE GALACTIC CLUSTER) the best open cluster - Messier 11 (ngc6705) - R.A. 18h 48m / DEC (-)06 20 - FANTASTIC!! OBJECT 11: (in Scutum) reference open cluster - Messier 26 (ngc6694) - R.A. 18h 43m / DEC (-)09 27 - small, 20 stars OBJECT 12: (in Serpens....to compare with Trifid nebula and associated cluster!) galactic cluster with nebula - Messier 16 (ngc6611) - R.A 18h 16m / DEC (-)13 48 - 6.4 mag. 60 stars! OBJECTs 13: Messiers 17 / 18 (nebula and cluster "Omega Neb.", ngc6618) - R.A. 18h 18m / DEC (-)16 12 - beautiful! OBJECT 14: galactic cluster - Messier 24 (ngc6603) - R.A. 18h 15m / DEC (-)18 27- bright! 45 stars! OBJECT 15: another galactic cluster - Messier 25 (IC4725) - R.A. 18h 29m / DEC (-)19 17 - very similar to Messier 24 OBJECT 16: What? Another galactic cluster? - Messier 23 (ngc6494) - R.A. 17h 54m / DEC (-)19 01 - 120 stars!!! OBJECT 17: (in Scorpius - for comparison, lest you forget....) Not satisfied....galactic cluster - Messier 6 (ngc6405) - R.A. 17h 37m / DEC (-)32 10 - nice, very LOW! OBJECT 18: (also in Scorpius, a repeat visit....) galactic cluster - Messier 7 (ngc6475) - R.A. 17h 51m / DEC (-)34 48 - bright but tough on horizon. OBJECT 19: wow! TRIFID nebular (Messier 20 - ngc6514) and cluster M-21 (ngc6531) - R.A. 17h 59m / DEC (-)23 02 OBJECT 20: The "Lagoon Nebula" - a MUST SEE object! best of the best - Messier 8 (ngc6523) - R.A. 18h 02m / DEC (-)24 20 - VERY large, bright, breathtaking!
A VISUAL GUIDE TO OUR DEEP SKY OBJECTS IN SAGITTARIUS (with help from Serpens and Scutum!)
Object 1 - Bright Star - "Nunki" (sigma Sagittarii) WHAT happened here....where's "Alpha??"
Every tour stars out with the brightest star in the constellation or area we are exploring.....normally that is the "Alpha star" from the early Bayer designation of Greek alphabet letters to designate the BRIGHTEST (alpha) to the dimmest (omega). But something has happened in Sagittarius. We are starting our "GO TO" TOUR in this case with the star NUNKI, or "sigma Sagittarii." So why not Alpha(??) the star known as "Alrami"? A quick look at the actual visual magnitudes of the brightest stars of Sagittarius (those mostly comprising the "teapot") are:
alpha - Mag. 4.11 - "Alrami"
beta (1) - Mag. 4.24 - "Arkab" ; beat (2) "Arkab Posterior" - Mag. 4.51
gamma - Mag. 3.07 - "Nash" / "Nushaba"
delta - Mag. 2.84 - "Kaus Medius"
epsilon - Mag. 1.82 - "Kaus Australis"
zeta - Mag. 2.71 - "Ascella"
lambda - Mag. 2.94 - "Kaus Borealis"
sigma - Mag. 2.14 - "Nunki"
So you can clearly see that SIX of Sagitarrius' brightest stars are DIMMER than Nunki, which actually outshines all the named stars of the constellation except "Kaus Australis!"
Nunki's dominance in early mythology and cultural lore makes it even more puzzling as to why Bayer did not designate this brighter star higher (at least "beta") in the Greek alphabet where the brighter the star the "earlier" its designation in the alphabet. From the Babylonian sancripts, Nunki was the star that signaled the rising of the waters: the "water constellations" of Capricornus ("sea goat"), Aquarius ("water bearer"), Pisces ("the fish"), Cetus ("the whale") and Pisces Austrinus ("the southern fish"). Referring to the "teapot" shape of the constellation, the ancient Chinese referred to Nunki as the "point star", where the handle connects to the "bowl" of the ladle that also can be imagined out of this asterism.
Object 2 - Globular Cluster in Ophiuchus (something to whet your appetite - Messier 14
To me, one of the most uninteresting of all globular clusters has been the relatively bright, but unresolvable globular cluster Messier 14 in Ophiuchus; hence, for the element of torture, we will start out globular cluster parade for this "GO TO" TOUR with that object so that you might compare with those seen following. For a full description of Messier 14 and its locale, please refer to my Ophiuchus GUIDE at http://www.weasner.com/etx/ref_guides/ophiuchus.html .
Object 3 - Messier 28 - A Fine Globular Cluster in Sagittarius
This is a very bright an highly concentrated globular located in the same wide field view as bright lambda Sagittarii, only 3/4 of a degree NW. It is extremely compact and will appear very much like M-14, above, except at magnitude 6.8 will appear brighter. It is VERY small compared to our next object, M-22, as it extends only 4.7' arc! Do not expect to see any stars resolved, even with the 8" scope; however, this is a bright and fine object - a bright "snowball" - in all telescopes; it makes a particularly outstanding sight in very low powers amidst the bright stars, particularly with the wide field ETX 60 and 70 scopes.
Object 4 - Now you are spoiled - Messier 22
Only 3 degrees from the rather mundane Messier 28 is the bright and large globular cluster Messier 22, which is twice as close to us as the fainter globular. At over 21' arc and magnitude 5.9, this is truly one of the BEST globular clusters for viewing! It is huge in low power and wide fields, and is a memorable sight on a very dark and moonless night. It is equal in every respect to the "granddaddy" of globulars, Messier 13 in Hercules. Some star hints can be appreciated even with the ETX 60 and 70 and the ETX 90 will clearly resolve stars around the perimeter of this large cluster. The ETX 125 shows stars all the way to the core, while the LX 90 can actually reveal the colors of the brightest red giant stars toward the middle of this remarkable cluster. For the record, most of the stars we see in this cluster of about 100,000 stars are magnitude 11, clearly definable in the ETX 90. It is one of the most "resolvable" of all globulars,perhaps even easier than Messier 13, except for its low altitude on the southern horizon.
Object 5 - Another Globular Cluster - Messier 75 - "tiny and tough!"
By astronomical standards this may be the most tightly packed - or seemingly so - of all globular clusters. Only Messier 80 (discussed in detail in my Scorpius "GO TO" GUIDE, http://www.weasner.com/etx/ref_guides/scorpius.html ) comes close to this degree of star concentration. However, it may be an illusion because of the TREMENDOUS distance of this object - almost 100,000 light years away! Messier 75, just on the Sagittarius/Capricornus border is beyond resolution in our telescopes and requires greater than an 18" to begin to see stars distinctly at magnitude 17. Nonetheless, this very distant cluster bears observing as one our most distant objects within the Milky Way galaxy; be careful with the ETX 60 and 70 to not confuse this 8th magnitude cluster with a faint star with haze.
Object 6 - A Good, Large and Very Open Globular Cluster - Messier 55
Messier 55 is an unusually large and open globular; although its total magnitude is a bright 4.4, its brightness is spread out over a large 10' arc area, making it more difficult than it would appear. Nonetheless, look for some resolution with the ETX 90 and very good resolution toward the center with the ETX 125 and LX 90 scopes. Even the ETX 60/70 should show some "mottling" of stars around the edges. The sharp-eyed observer will clearly notice that M-55 is elongated in a north-south direction. Although most visible stars are about 13th magnitude, the "glow" that you will see in small telescopes is a result of thousands of stars to magnitude 17 and beyond in this very large object.
Object 7 - Easy-to-Find Globular Cluster Messier 54
Here is an easy object and a very spectacular sight in the wide field views of the ETX 60 and 70 as well as with the good wide field oculars of the larger telescopes. It is only 1.5 degree west and slightly south of zeta Sagittarii (see chart). This cluster is a bit different than most and certainly different than M-55 above in that it is a fairly uniform brightness across, but suddenly increasing dramatically in brightness toward the center, almost like a large nucleus. It is a VERY small globular, only 2.1' across, and very difficult to resolve; look for only peripheral stars to be seen using averted vision with the LX 90; smaller scopes show only a diffuse glow with a clear bright "core."
Object 8 - Another Globular....and this one is tough! Messier 70
This object and Messier 69 (below) make an interesting wide-field pair in the ETX 60 & 70 telescopes. Both globulars are very small objects. Messier 70 is only 2.5' across and a tough magnitude 9.1, making it almost star-like in low powers and wide fields. Medium magnification is best on both this and M-69, which is also only 2.9' across and magnitude 8.9. These clusters, like M-75 are very distant - some 69,000 light years - hence their faintness and lack of detail. Do not expect any detail in scopes under 18-22" diameter.
Object 9 - Messier 69 - Twin to M-70, above
Look for this globular, appearing almost identical to M-70, about two degrees west. Only about 4' arc north and a bit west of the cluster is a very reddish-appearing 9th magnitude star that makes an interesting contrast to the diffuse appearance of this roundish globular. For details of M-69, see M-70 above.
Object 10 - No More Globulars! Our "Standard"-setting Open Cluster - Messier 11 (in Scutum)
If you can find a finer and more breath-taking open star cluster than Messier 11 (the "wild duck cluster"), then you are observing from a different planet. Messier 11 in Scutum sets the standards for all galactic star clusters, so I wanted you to remember this one first before moving on to the nice open clusters (but none to compare) in Sagittarius. For a full discussion of Messier 11, refer to the "GO TO" TOUR of Scutum in: http://www.weasner.com/etx/ref_guides/aquila.html .
Object 11 - Another Open Cluster in Nearby Scutum - Messier 26
Not particularly exciting, I wanted you to first glimpse Messier 26 AFTER seeing the magnificent M-11 and BEFORE going onto the clusters in Sagittarius to make you more appreciative of what you are about to see in the beautifully-star-packed wide field views ahead. A full discussion of Messier 26 is also found at http://www.weasner.com/etx/ref_guides/aquila.html .
Object 12 - Messier 16 - Galactic cluster in Serpens
This is included since it is part of the magnificent "arm" of stars of this region of the Milky Way which includes the marvelous Messier 24, the Lagoon Nebula, the Trifid Nebula, Messier 23, and so many more packed areas of stars. In Serpens, this object is very tightly compacted, yet clearly resolvable in all of our telescopes. It appears as a very star-poor globular with stars resolvable even in the ETX 60 and 70, most of which are within the same magnitude range. This makes a very fine low power object for larger telescopes using wide field eyepieces as it is in a great star field of the Milky Way; look for the incredible large cluster Messier 24 due east of this tiny group of stars, and the famous "Lagoon nebula" (M-8) almost due south. This object is just inside the right field of the following wide-field photograph.
Objects 13 - Galactic Star Cluster Messier 18 and "The Omega Nebula", Messier 17
The star cluster known as Messier 18 may be somewhat of a disappointment. At magnitude 7.5, it contains about 15 stars spread over an area of 12' arc. In a field wider than one degree, you can get BOTH Messiers 17 and 18 in the same field of view, with the cluster being about 1 degree south of the beautiful Omega Nebula, Messier 17. (SEE PHOTO BELOW) These objects are actually about 1000 light years apart in space, with the cluster being in the foreground from our vantage point. Messier 17, also known as the "Swan Nebula" and the "Horseshoe Nebula" is about 7' arc long and some 2' arc across with a visual magnitude of only 8.9.....misleading. This nebula can clearly be seen on a very dark night in even binoculars and is an outstanding object. If the sky is dark enough, be sure to look for the distinctive "hook" shape, conforming to the "swan's head." Like so many bright nebulae, M-17 appears to be associated with about 20 nearby stars, perhaps not unlike the association of the famous Orion nebula to the stars within its vicinity. Use very low powers to observe Messier 18 (the cluster) and about 75x in all scopes for the Omega nebula to increase the contrast of this very faint cloud of gas.
Object 14 - Huge Open Cluster - Messier 24 (see wide field photograph preceding)
Also known as the "small Sagittarius star cloud" this is an outstanding wide field object, and is clearly visible to the unaided eye on a moonless night. Although not accurately described as such by Charles Messier, this has been assigned as his 24th object....what he recorded was a tiny 4' arc cluster at this position, and surely this galactic cluster has not grown so greatly in 250 years! M-24 has a diameter equal to three full moons - 1.5 degrees! It is resolvable in the ETX 60 and 70 as a magnificent cloud of stars and larger telescopes do not do it justice. It is a true wide field object. Scanning through this cloud with very low powers reveals hundreds of thousands of seemingly tiny stars, all of nearly equal magnitude. Compare the prime location of this object relative to the other fine objects in the Sagittarius Milky Way.
Object 15 - Messier 25 - Galactic Cluster (see photo for location!)
Located immediately east of M-24, this may seem quite a letdown after the magnificent array of stars within Messier 24. However this is a very rich and deserving cluster of stars, easily resolvable in the ETX 60 and 70 and a beautiful sight in very low power views with the ETX 90 and larger instruments. Note in low powers on a very dark night the "strings" of stars that are visible from the center of this cluster, notably in a NW direction (to upper left in your ETX/LX eyepiece orientation), SW (lower left), and in a near eastward path (to the right). Since all 50 stars of this cluster are 12th magnitude and brighter, all should be seen on a very dark night with the ETX 90, and should be very easy in the ETX 125. There are perhaps 12 stars magnitude 9 and brighter and that gives a remarkable 3-D appearance to this 2000 light-year-distant cluster. One of the brighter stars is U Sagittarii, a notable Cepheid variable star (see our "GO TO" GUIDE on Draco/Cepheus...at http://www.weasner.com/etx/ref_guides/draco.html . This star, varying between magnitude 6.3 and 7.1 in a period of only less than seven (7) days, is an ideal star for beginner variable star observers. The finder chart I have adapted below has been REVERSED for orientation to match the field of view of the ETX/LX telescope with NORTH at TOP, EAST at RIGHT.
This finder chart is about one-half degree (about the size of the moon's disk) across, and very nearly matches the field of view of the ETX 125 with the 26mm Plossl eyepiece. For a more detailed observing chart complete with magnitudes of comparison stars, download, save to file, resize and print the American Association of Variable Star Observers chart for R and 350 Sagittarii (which will include U Sagittarii in the wide field of this "a" finder field chart) at: http://charts.aavso.org/SGR/R_SGR/RSGR-A.GIF
Object 16 - Another Galactic Cluster - Messier 23 - A MEMORABLE SIGHT! Do Not Miss This One!
This is a beautiful star cluster, very rich and located immediately west of M-24 about four degrees. Wide field eyepieces are a must for this grand and large cluster which contains no less than 120 stars and covers one-half degree of sky! If you observe with the larger ETX 125 and/or LX 90, be sure to use your lowest magnifications and widest fields possible. This is an ideal object for the wide field ETX 60 and 70, with stars scattered like jewels strewn across black velvet of the sky. Star magnitudes range from about 8.5 to 12th, so nearly all stars are visible in at least the ETX 90. There is one brighter star of magnitude 8.1 to the northeast side of this large cluster and a very bright (magnitude 6.5) star about one cluster diameter to the northwest. Look for a distinct "chain" of tiny 10th magnitude stars that bridge from the center of the cluster to this brighter star. Note: this brighter star is NOT part of the 2000 light year-distant (same as Messier 25!) cluster.
Object 17 - Messier 6 - Open Cluster in Scorpius (Can't Bypass This One...."in the neighborhood!")
Be sure to re-visit this beautiful open galactic cluster in Scorpius while you are so close....it's only a bit to the west and sure to be a hit under dark skies! Almost the same size (25' arc) as Messier 23, above, but containing only about 50 stars, this 5.3 magnitude object is discussed in full in our "GO TO" TOUR guide to Scorpius at: http://www.weasner.com/etx/ref_guides/scorpius.html . I have put this galactic cluster in our current Sagittarius Guide as a comparison of the MANY Milky Way arm clusters that are all located at near the same distance from our Earth.
Object 18 - Messier 7 - Another Scorpius Comparison Galactic Cluster
Also in Scorpius, this one is so much different in appearance that it bears a second look in comparison to the very dense and rich clusters of Scutum and Sagittarius. M-7 contains only about 50 stars, all visible in our scopes at very low power, but these stars are spread over a LARGE on-degree area, and thus the true "cluster" nature of this object is all but lost in telescopes other than the ETX 60 and 70. For more information see: http://www.weasner.com/etx/ref_guides/scorpius.html
Objects 19 - THE TRIFID NEBULA (Messier 20) and associated galactic cluster Messier 21
This object is a treat in nearly all telescopes used in very dark sky conditions. Located in the same wide field (about 1 degree) field of view, look for the galactic cluster M-21 as a grouping of stars about 12' arc diameter; the stars range in brightness from 8th to 12th, with about 10 of them brighter and the rest dim. Look for a very yellow star with a close companion that should appear somewhat grey in color...you can't miss this pair - the yellow star is magnitude 9 and the grey one only a magnitude dimmer; use medium-high (about 125x) to view this pair. The famous TRIFID NEBULA (M-20) is only about 3/4 degree from this nice cluster to the southwest (see accompanying photos). This remarkable object is familiar to all of us from photographs, as three equally-shaped and equally-bright wedges of "pie" of blue and red. Indeed, on a very dark night, the larger telescopes "may" be able to hint at this true color of the nebulosity. Often overlooked, right in the middle of this wonderful object, are three stars - magnitudes 6.9, 8 and 10.5. Our smaller telescopes can only resolve the TWO brightest ones, however. With high magnification and steady seeing, the ETX 125 and LX 90 might reveal the third dimmest star at about 5.5" arc from the brighter pair. The human eye cannot, unfortunately do this object - nor its rival, Messier 8, the "Lagoon Nebula" justice as seen only in photographs like that below, taken with the magnificent 120-inch telescope at Lick Observatory. Note the conspicuous dark "lanes" which trisect this bright nebula into its three components; the ETX 90 and larger telescopes are capable of showing these three rifts easily on moonless, dark nights.
Recent studies suggest that this nebula and associated stars are located at almost the same distance from us as the fabulous Messier 8, Lagoon Nebula, and hence are likely to be part of a greater association of objects within the rich Sagittarius arm of our own galaxy.
Object 20 - THE LAGOON NEBULA! - Messier 8
The magnificent view afforded by the Sagittarius star cloud (seen to the right in the photograph above) provides us with a small glimpse of one inner arm of our congested and star-studded galaxy. Within that arm is the wealth of nebulae, stars, clusters and objects that are not unlike our own solar neighborhood....only more of them packed more densely together. In this photograph you can clearly see the Trifid Nebula (messier 20) and below it the huge and very bright "Lagoon Nebula," or "Omega Nebula" (as coined by William Herschel as he could see the Greek symbol for "omega" in the nebulous cloud). This very bright cloud of stellar gas envelopes a tiny star cluster - NGC 6530, to the nebula's east, which contains about 25 very faint stars. In small telescopes, the "omega" shape might be missed and the object will likely appear as an oval with some mottling, or dark detail. Visible to the naked eye and clearly distinguishable in your finderscopes, Messier 8 shows a tremendous amount of dark and bright detail....in addition to a wonderful "sprinkling" of stars....in the ETX 125 and LX 90 scopes. Together, this swarm of stars and associated nebulosity make this one of the summer's highlights from your dark sky sight! Look for the two brightest stars (both 9th magnitude) to be at the western edge of this nebula, and very near one-another, like a double. Another interesting feature is the very dark nebula (dark dust cloud) B88 which can clearly be seen in a wide field with the ETX 125 or LX 90 on a VERY dark night; this dark cloud is nearly in the center of M-8, just a bit to the west.
Perhaps it is not so much this marvelous Lagoon that is so intriguing in this part of Sagittarius as is the phenomenal array of stars, clusters and associations that abound here. Take the time.....turn off the motors....put in the widest field eyepiece you can find....and just scan until you lose yourself in the remarkable Milky Way centered on Messier 8. This is undoubtedly one of the star-richest areas of sky of all and worthy of repeated visits, and prolonged stays while you explore to your heart's content.....
WANDERING ABOUT....YOUR NEW "USER OBJECT" IN SAGITTARIUS
And you really thought I would keep my word about "....no variable stars." Well, we can't let this one go by. The remarkable variable star RY Sagittarii is so easy, so quick and so readily accessible, that you should add this star to your list of "USER OBJECTS" for your AutoStar. If nothing else, you can have a finder chart and a link to the AAVSO observing charts and information. And, certainly RY Sag is visible in all telescopes, from the ETX 60 to the LX 90. This is one of the most unusual of all variable stars, in that it is normally about magnitude 6.5 to 7.0, but suddenly and totally unpredictably.....it will dim dramatically to less than 12th magnitude where it will stay for as much as 200 or more days! As a "R Coronae Borealis" type star, RY Sagittarii is the best of southern such stars for observing. When brightest, it is easily within reach of all our telescopes....when suddenly dimming, even the ETX 90 can reach it and monitor its wild fluctuations until it returns to its "normal" near-naked eye brightness! The following sample light curve gives you an idea of the normal brightness (highest point) of the star and its sudden demise to very faint magnitudes that may last for nearly a year.
The following link will patch you into the AAVSO star chart "a", which is the low power, wide-field finder chart for the star; when at brightest, this star chart will suffice for comparison star magnitudes; however, when dimming either the "b" or "c" (medium and narrow field, respectively which show fainter and fainter stars) should be used to follow the irregular fluctuations of this interesting cataclysmic star.
The coordinates for RY Sagittarii to enter as a User Object are: R.A. - 19H 13m / DEC - (-)33 37. On AutoStar, go to: "Select/Object [enter]...." scroll down to "User Object" [ enter]. Now enter the coordinates given above for "RY Sagittarii" - , using the number keys on AutoStar. After entering the coordinates and pressing "Enter" yet again, scroll down one and you can list the magnitude of the object as "6"[Enter].
Next Constellation "GO TO" TOUR Installment: COMA BERENICES....the sprinkling of Berenices' hair high in the skies of northern latitudes amidst the dark skies; although we have touched briefly in this constellation in previous "GO TO" GUIDES, this close-up look will provide an in-depth study of some of the fascinating objects in this very rich area. For teasers, it is interesting that there may well be galaxies in the millions that are actually photographable through very large telescopes and the Hubble Space Telescope within this very small and often overlooked huge cluster of stars!
You will be amazed at the incredible number of "faint fuzzies" that Mr. Messier did not see as you scan slowly through this area on your darkest nights!
Good Observing and explorations of this wonderful world of deep space!
P. Clay Sherrod
Arkansas Sky Observatory
Conway / Petit Jean Mountain
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