CONSTELLATION GUIDE Last updated: 30 April 2001

"GO TO"....HERCULES
Hanging Out With "Hercules the Hero" With Your ETX and LX 90 Telescope

From: sherrodc@ipa.net (Clay Sherrod)

ABOUT THE CONSTELLATION "GO-TO" GUIDES!

This installment of the constellation HERCULES is the fifth guide, "GO TO HERCULES"- of our constellation study guides for ETX and LX 90 telescope users - you will learn more about the fantastic globular cluster Messier 13, other star clusters and many nice double stars in this large spring/summer constellation. As will all of our "GO TO GUIDES", it features a "start" with an easy GO TO to the bright star RAS ALGETHI as your beginning point for a "GO TO TOUR

From bright starry globular clusters to beautifully-colored and complex multiple star systems, discussions along the way tell you what to expect from each telescope size and type. All objects will be discussed with exact descriptions of what the viewers of the ETX 60/70, ETX 90, ETX 125, and LX 90 should expect to see...and what to NOT expect to see!

As in all Guides, useful magnifications for EACH GO TO object are discussed for certain telescopes, what type of night and conditions are needed to see certain details, double stars that can be resolved in each telescope model, and much, much more. It is your complete GUIDE for your deep sky observing pleasure and a very handy tool for use at your next star party!

Needless to say, it WILL put your AutoStar to work for you in a most efficient and enjoyable way!

I hope you will enjoy these comprehensive GUIDES to "Touring the Constellations" which will feature a NEW constellation about every two weeks, complete with diagrams, charts and illustrations. Please let us hear from you with summations of YOUR observations through these constellation tours!

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Introduction -
Hercules (pronounced "HER-kew -eez") is one of the largest of all constellations and dominates the seemingly bright-star void skies of spring and early summer. The Greek hero of the sky appears ready to fend off any celestial offenders it might encounter, the snakes, dragons, scorpions, bears, wolves and all else that the ancient Arabian and Greek skywatchers filled into our frightful night sky. Indeed, without the fearsome duo of Orion and Hercules (perhaps a good comic book venue) the darkened gloom of night with its creatures might seem a very uninviting place for the innocent likes of Cassiopeia, Virgo, Coma Berenices, Venus.....

Hercules gained his place in the heavens after a rewarding and eventful life of fighting crime and evil injustice on the mortal Earth; he subdued the evil bull of Crete, freed Prometheus from his enslavement in the Caucasus mountains, guided the famous Argonauts on their epic voyage, slew the Lion of Nemea, clubbed to death the horrible attacking Birds of Sytmphalia. But even Hercules can only do so much. It seems that, either from vainity or the chill of the night air when not fighting the evil forces of mythology, he donned a warm and glamorous robe which - unknown the celestial crime fighter - had been soaked in the blood of the sure-to-kill-you-no-matter-who-you-are-Centaur Nessus. The poison gradually pulled all of the strength, stamina and fortitude from our hero and he opted for death rather than a sure demise in shame and geekdome.

Hence, Hercules was cremated atop Mt. Oeta on his way to the Heavens where he gained his place among the immorals among the star group that we see today.

To even the most ancient of ancients, Hercules has be denoted as "the Kneeling One," or "kneeling man of strength" and his place in the stars frequently depicts him in that position. HOWEVER, in Greek mythology, only after his death did Hercules realize his lifelong quest to marry the fine Princes Here, daughter of Hebe of Eternal Youth. It has always been my opinion that we are seeing Hercules in a very weak moment (perpetually through all time....) kneeling in proposition of marriage to his childhood sweetheart.

But I digress....perhaps we should remember this great man of 12 wonders more fittingly from the striking and manly figure shown above.

The click-on chart shown below can be downloaded to a file on your computer, resized in that file and printed as a complete star reference chart for these four constellations. Each of the reference numbers apply to the concise listing of objects found following.

Click for full size version.

Among the outlining figures within the constellation of Hercules is the somewhat famous "Keystone", a marker of the springtime skies. This "asterism" or star pattern is comprised of four stars in the traditional keystone shape marked at the corners by the fairly bright stars PI (mag. 3.4), ETA (mag. 3.6), EPSILON (mag. 3.9, and ZETA (mag. 3.0).

Immediately East of Hercules is the familiar constellation of LYRA, the harp with its very bright white star Vega, a beacon of early summertime skies. This small constellation will be featured in later installments of the GO TO Constellation Guides.

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YOUR HERCULES CONCISE DIRECTORY

In Hercules, there are 10 nice objects in this GO TO tour; all are in reach of every telescope in our "ETX and LX family" yet each telescope will demonstrate uniquely different and challenging aspects of the objects. You will note that there is a conspicuous absence of brighter galaxies and open galactic clusters in this region of the sky. Immediately South of Hercules, we have seen that there are an overwhelming number of globular clusters in Ophiuchus and Serpens, and innumerable distant galaxies in Coma Berenices, Ophiuchus and surrounding areas.

As we look toward the constellation Hercules, we are looking ABOVE the galactic pole, and hence looking AWAY from the star-rich areas of our own galaxy, the Milky Way. Hence the star concentration and the number of rich star clusters diminish as we move upward, away from the "hub" of the galaxy. However, note that in the figure below, the GLOBULAR CLUSTERS are distributed fairly evenly around the galactic center, so there are at least two very rich such objects in our TOUR of Hercules.

As will all of our GO TO TOUR GUIDES, I continue to recommend good a good star atlas and/or chart which lists the finest objects constellation-by-constellation; if you cannot access any of these objects (or those that are not listed in this TOUR), you can access directly from coordinates - Right Ascension (RA) and Declination (DEC) of any known object via the AutoStar. You merely need to hold down your MODE key on the AutoStar for three (3) seconds and the RA and DEC coordinates appear for the telescope. Merely press "GO TO" and the cursor appears prompting you to enter the Right Ascension of the object if it is NOT listed among the objects in the AutoStar library; once the RA is entered, press "Enter" and the cursor once again prompts for the Declination coordinates (these coordinates for epoch 2000) are found in all good observing guides). Once those are entered, merely press "GO TO" once again and your ETX or LX 90 will slew to the position of the object!

Detailed descriptions of each object of this TOUR will be described and specifics provided as to visibility of those objects in YOUR telescope model. The constellation tour star chart (click on and print to size, above) will get you started, as it demonstrates the relative positions of all 10 objects in this "Hercules tour."

Following is the summarized 10-object list for your "GO TO TOUR" of Hercules; you may wish to find the majority of the objects from the AutoStar library (for example, you can merely pull up Messiers 13 or 92 by going to "Object/Deep Sky/Messier Object/"13"....enter....GO TO" or...if you want to experiment and be a "better AutoStar user", try entering the following coordinates (provided in the list directly following) as described under MODE above.

OBJECT 1:
    bright star - Ras Algethi (alpha Herculi) - R.A. 17h 12' / DEC + 14 27 -  Magnitude:  3.9 (a bit variable)
OBJECT 2:
    "optical" double star - Delta Herculi - R.A. 17 13' / DEC + 24 54 - Magnitudes: 3.1 & 8.5
OBJECT 3:
    good double star - Rho Herculi - R.A. 17h 22' / DEC + 37 11 - Magnitudes: 4.5 & 5.5
OBJECT 4:
    nice - but tough "triple" star - Mu Herculi - R.A. 17h 45' / DEC + 27 45 - Magnitudes:  3.4, 9.8, & 10.8
OBJECT 5:
    U Herculi (68 Herc) nice easy variable star - - R.A. 17h 16' / + 33 09 - Mag. range: 4.6 to 5.5 (2.1 days)
OBJECT 6:
    nice double star - 95 Herculi -  R.A. 17 59' / DEC + 21 36 - Magnitudes:  5.1 & 5.2 (color contrast??)
OBJECT 7:
    THE globular cluster - Messier 13 (ngc6205) -  R.A. 16h 40' / DEC + 36 33 - Magnitude:  4.0 (wow!!)
OBJECTS 8:  
    globular cluster - Messier 92 (ngc6341) -  R.A. 17h 16' / DEC + 43 12 - Magnitude:  6.1 ("little brother")
OBJECT 9:  
   very faint globular cluster - ngc6229 - R.A. 16h 46' / DEC + 47 37- Magnitude:  8.9 (nice object)
OBJECT 10:  
    faint planetary nebular - ngc6210 - R.A. 16h 43' / DEC + 23 53 - Magnitude:  9.7 (star is 12.1!)

GOOD LUCK on these objects....there are a few nice challenges ahead as described in the detail summaries for each object provided below!

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A VISUAL GUIDE TO OUR OBJECTS IN HERCULES -

Object 1 - Beautiful Double Star and Bright Star RAS ALGETHI (alpha Herculi)
You cannot find a more beautiful double star than RAS ALGEHTI. This is our starting star for our TOUR of Hercules and a very nice one, indeed. Comprised of it main star of magnitude 3.9 and very, very red in color, it is accompanied by an easily resolvable companion of Magnitude 5.4 that has been described by many as "emerald green!" You don't get that color contrast too often...it is absolutely gorgeous and perhaps the best object on your tour, even rivaling the magnificent Messier 13 later on down your list!

You will never forget your medium power (about 15x per inch) view of this double star; it will be firmly implanted in your memory just like your first view of the rings of Saturn! It is quite easy in the ETX 90 and larger scopes and resolves with medium power very well....higher powers are recommended to really separate the two to appreciate the wonderful color contrasts. For the ETX 60 and 70, use fairly high power to separate, as they are pretty close for those scopes at only about 5" arc separation, but clearly resolvable in the smaller telescopes.

Alpha Herculi is also slightly variable, ranging from about magnitude 3.2 to around 4.0 at dimmest in a period of about 90 days. At only 420 light years away, it is a mass just about like our own sun, but about 800 times more luminous!

Rasa Ras gets it Arabic name from "Ras al Jauthiyy" or, "...head of the kneeling one," as described above. In ancient China it was given a bit more significance, surprisingly so for such a faint naked eye star, and was signified the "Emperor's Throne", quite a lofty perch for a fairly seemingly obscure star.

Object 2 - "Optical Double" Star SARIN (delta Herculi)
This double star is an "optical double" as has been described in previous constellation Guides. An optical double is one that APPEARS from our vantage point to be a binary, but in fact is only "lined up" to our sight as two stars seemingly very close. Sarin, at magnitude 3.4, has an optical companion of 8th magnitude nearly due south from the brighter star, and clearly both stars are moving perpendicular to one-another so they are NOT physically bound. Like Ras Algethi above, this double has a wonderful color contrast that can be clearly seen in the ETX 125 and LX 90, but not so easily in the ETX 90 and smaller scopes. The brighter star is somewhat a green or bluish color and the dimmer star is clearly either greyish white or slightly pinkish-white, depending on your color acuity. With a present separation of about 5" arc, this star CAN be resolved in all of our telescopes, although high magnification IS required on the ETX 60, 70 and 90 to find the very faint star; be sure to look for it just west of due south.

Object 3 - A Good Double Star - Rho Herculi
This is a nice and easy double star for all of our telescopes. With an orbital period (this is a true double star system) of just more than 56 years, the apparent angular distance of these stars varies enough to allow a good separation (4.1" arc) at the present time. This is a very close star to Earth, at only 30 light years distant, and is a star in the "red-giant" making phase, very much more luminous that our Sun but about the same size in its "pre-expansion" period. This star can be best seen with about 100x in the ETX 90 and about 77x in the 125 and LX 90...more magnification will provide better views. This object requires about 50x per inch aperture for good resolution in the ETX 60 and 70.

Object 4 - A fine - but challenging - Triple Star - Mu Herculi
This is one of the most-observed of all triple star systems. It is, indeed, a physically associated triplet of stars, all orbiting one-another. Mu, the primary star at magnitude 3.4, has a VERY faint (mag. 9.8) companion nearly due west about 34" arc (slightly smaller than Jupiter appears in whatever eyepiece you are using). It is a very difficult star to find due to the brightness of Mu itself, so I highly recommend finding Mu first at low power, centering, and then increasing the magnification to about 25x per inch to locate the companion. The companion star itself is a challenge for the ETX 60, 70 and 90. In the ETX 125 and LX 90.... ONCE FOUND....increase the magnification even more (hope you are tracking well tonight!) to split the faint star into TWO stars! On my ETX 125, this requires the very best of nights and I have never had a true separation, only an elongation of the image. The LX 90 will resolve the very faint star into its two red stars at an incredible 848x (the 4.7mm + barlow)!! It will NOT resolve the star at lower magnification, so don't get your hopes up. These two are actually a pair of RED DWARF stars, but will appear for whatever reason a rather bright blue color! Good luck on this one!

Object 5 - A Very Good Variable Star - uHerculi (or "68 Herculi")
For out ETX 60 and 70 users out there, this is a "DO NOT MISS" variable star for you....and for all scopes, even binoculars! This star is variable from magnitude 4.7 to 5.5 in a period of ONLY 2.1 days! This variation should be compared to other brighter stars seen around it (use the locator chart from the American Association of Variable Star Observers that I have provided the link to below) to judge its brightness during this rapid cycle and record what you see! Download and print the AAVSO chart (this is a low power, wide field "finder chart" that allows you to find relatively bright stars over a large part of the sky for comparison.....sky directions are indicated on the map):

http://charts.aavso.org/SER/R_SER/RSER-A.GIF

After you have observed this star in comparison to stars of equal magnitude (you will get better with practice) you can compile a graph of the brightness changes similar to the one shown. These "light curves" as they are called, are frequently included in these constellation Guides to show the remarkable changes in a star's brightness over time.

Object 6 - Another Double Star....but hold on! It's Worth Looking At!! - "95 herculi"
This magnitude 4.4 star is a famous double star and well worth looking up. Actually the total brightness of 4.4 is a COMBINED brightness of two stars, magnitudes 5.1 and 5.3 that are fairly close together, but easily resolvable in all of our telescopes. Use higher power (about 30-40x per inch) on the ETX 60 and 70 and medium power (about 15x to 20x per inch) on the ETX 90 and larger scopes to resolve. The stars, almost equal in brightness, are about 6" apart, so they should be readily seen at these magnifications.

There is a very interesting aspect of these two curious stars....they change color (or so it appears). At one point in 1856 for example the stars were both recorded as "white." In 1857, the observer, Piazza Smyth was amazed to see that both stars then were recorded as green and deep red! Curiously, this same phenomenon was observed by experienced and highly reputable observers WORLDWIDE during that same time period! Even more curious, is that the stars appear to have "returned" to the whitish coloration since and have not shown signs of any other colors since!! These two stars are giant stars some 400 light years distant.

Without a doubt, this is the most famous of all northern hemisphere globular clusters and one of the most notable deep sky objects for all telescopes. It is rivaled in beauty only from the Omega Centauri globular and 47 Tucanae globular clusters which are much brighter and larger in telescopes. Omega Centauri is clearly visible for the lower United States observers and those south of any latitude 32 degrees north, but atmospheric extinction usually precludes the excellent views afforded by Messier 13.

"Messier 13" was actually first cataloged by Edmund Halley (of comet fame), but credit is given some 50 years later (1764) to Messier as his 13th entry into his "you-may-confuse-this-for-a-comet" objects. Very high in the northern skies and conveniently located in the "Keystone" noted above, this cluster is actually visible to the naked eye and makes a nice sight even in your finderscope, the total expanse equaling about 1/3 the diameter of the moon!

The cluster is clearly visible in all of our telescopes, and can be "partially" resolved around its edges even with the ETX 70 and high magnification (about 120x) on a very dark night. Many peripheral stars are seen with the ETX 90 and the 125 begins to break down the central core into multitudes of very faint 11th magnitude stars. The view with the LX 90 is incredible under medium high (about 227x) power, with star colors becoming evident with the red giant stars within the central part of the cluster. However, with any amateur telescope, there is still an unresolved "glow" of stars to the 21st magnitude which are thought to number in the 40,000's.

Be sure in all scopes under VERY dark conditions, to look for the many "star strings", arm-like extensions of stars that are clearly evident under good conditions and medium magnification; these are visible in virtually all of our telescopes, but really begin to take on a distinct nature with the ETX 125 and LX 90 aperture. In my ETX 125 and LC 90 there is a very pronounced "string" in a rather NW direction that almost appears as an "arm" of stars extending quite a ways from the central core.

This incredible object measures over 160 light years across, and is some 25,000 light years distant, or about hovering over the center of our Milky Way galaxy. Some outlying stars are thought to be gravitationally-bound to M-13 out to the incredible distance of 200 light years. An interesting aspect concerning ALL globular clusters is necessary here: even though, at this great distance, they APPEAR to be packed and crowded with multitudes of tightly-packed stars, in actuality they are so large that there is LESS than one star per cubic light year in each! That is barely one-half the distance of OUR closest star system, Alpha Centauri!

Object 8 - Messier 92 - Nice Globular....but Overshadowed by its Big Brother to the South!
It's tough to be in competitions that you know you can't win, and little Messier 92 is clearly in that no-win situation, located just north and slightly east of its "big brother globular" Messier 13. As nice as ANY celestial object is in reality, it almost seems useless to look at Messier 92 after you have viewed the expansive beauty of the huge Messier 13.

Unfortunately for this often overlook globular, it is truly a spectacular objects - in many ways more so that Messier 13. At first glance....particularly after seeing M-13....you may not think so as this globular requires a bit more dark sky and somewhat higher magnification with all of our telescopes. The FIRST thing you should notice is that it has an incredible dense concentration of stars all across the center of the cluster, much more so (compacted) than M-13 and many other such globulars. Indeed, the object is so hard to penetrate even with the ETX 125 and LX 90 that star resolution is confined to the peripheral parts; however even the ETX 60 and about 120x will resolve SOME outer stars in this magnitude 6.1 cluster. At a distance of over 35,000 light years, its far distance compared to M-13 can only suggest how this cluster would appear if at the same distance! For the ETX 90 and larger telescopes, observing with a very well dark-adapted eye on a dark night with about 30x per inch will actually reveal a much more incredible sight than its rival M-13!

Object 9 - NGC 6229 - A faint and distant globular cluster
If you thought that M92 was small compared to M-13, just wait until you see this one! This very distant globular cluster is located very near the more famous pair in our skies but is a very difficult object. In the ETX 60 and 70 at medium power, this will appear as a very fuzzy and dim 8th magnitude star. Only the "glow" instead of a point of light eludes to its non-stellar nature in those scopes. The ETX 90 does only a bit better, but with higher power, it will begin to appear as a glowing ball of light. There is no resolution of this cluster in ANY of the ETX nor LX scopes. At magnitude 8.5, this tiny-appearing globular extends only 3.5' across, compared to M-13's whopping 23' and M-92's 8' arc.

Object 10 - Planetary Nebula NGC 6210
This also is a tough object but is included here because of the seeming void of any nebulae to observe in Hercules; indeed, were it not for M-13 and M-92, Hercules would be a very dull constellation other than its hundreds of striking double and multiple star systems! NGC 6210 is a very difficult, magnitude 9.7 planetary nebula, the remnants of a stellar explosion. The "remains" - a tiny 12th magnitude star at the center of this very blue disk-like object can be seen under good dark skies and about 227x with the LX 90 and can be occasionally glimpsed in the ETX 125 on very steady nights at the same magnification. The disk can be seen clearly in the ETX 90 as 20" arc elongated "dot" (about one-half the size Jupiter appears in the telescope at the same magnification). Its color makes this a "must see" for the larger telescopes.

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WANDERING ABOUT....YOUR NEW "USER OBJECT" FOR HERCULES

This brief GO TO Tour of Hercules has revealed its most interesting objects. But please do not stop here. Go ahead and locate many of the hundreds of objects that are present in Hercules.....there are several more interesting double and multiple stars that are within the reach of your telescope. In addition, use this opportunity to actually LOAD ANOTHER USER OBJECT onto your AutoStar!

This featured user "GO TO OBJECT" is much different than all the rest of those we have loaded before. This is an object we CAN'T SEE. No, it is not a black hole....but just as good. What you are about to load is a very famous nova, or "exploding star" from 1934, "Nova Herculis" or DQ Herculis as it is now known. This was one of the most brilliant novae of our last century, attaining a brightness of nearly +1.0 on Christmas morning, 1934. Prior to that time, the star was captured on film as nothing more than a common 15th magnitude object in Hercules....by December 13 it had suddenly brightened to 3rd magnitude and kept increasing from there! At its peak DQ Herculis reached a brightness that would compare to 65,000 times our own sun at that distance!!

It took nearly 90 days for the star, located just on the Hercules-Lyra border, to suddenly begin fading and today it is believed to be a dwarf star. It can still be seen with some MAJOR brightness fluctuations from its average brightness of about 9.2 however, and well worth checking as often as possible....that is why I have selected DQ Herculis as your USER OBJECT in Hercules. It is visible in all of our telescopes and you never can tell when the NEXT outburst will occur. The chart link below will allow you to download and print out the appropriate AAVSO chart for DQ Herculis....other wider field and more narrow field charts are available from the same link's home page:

http://charts.aavso.org/HER/DQ_HER/DQHER-B.GIF

To load this nova on your User Object on AutoStar, go to: "Select/Object [enter] and scroll down to "user object" [enter]. Now enter these coordinates: R.A. 18 06' / DEC + 45 51' ; under "description" enter "DQ HERC NOVA" You will now have a wonderful "cataclysmic variable star" to monitor. If you suddenly see an outburst of this star, by all means....REPORT IT to: www.aavso.org immediately!

Next Constellations "GO TO TOUR" Installment: DRACO, with discussions of Cepheus and Ursa Minor...you don't want to miss this one!

Good observing and explorations of the wonderful world of deep space!

P. Clay Sherrod
Arkansas Sky Observatory
Conway / Petit Jean Mountain
Arkansas

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