Last updated: 13 December 2001
"GO TO"....ORION - - The Marvelous Stars of the Winter's Hunter
....the most unforgettable constellation of the cosmos....
- Revealing the Treasures Within
YOUR CONCISE "GO TO" TOUR for Orion
As the 34th Constellation Guides, "GO TO ORION" - Revealing the Treasures Within, we conclude the Constellation Guide for this magnificent winter grouping. We began with a complete historic and general-interest overview of Orion in Part I followed by a detailed look at the environs in and around Messier 42, the Great Orion Nebula. Here we once again enter the ranks of our "GO TO" Concise Guides of deep sky objects and interesting double/multiple stars for computerized telescope.
This three part series has been a wonderful test of my concentration, as Orion presents so much fascinating information, objects, history and incredible sights, that focusing in on pertinent objects and information has been quite difficult. There is so much within Orion's borders that unfortunately for space restrictions had to be left out. However, I certainly urge all observers to obtain a very good handbook and star atlas (or computer Sky program) and study the wealth of fine objects found here. As for printed handbooks, no one should be without the tremendous reference books "Burnham's Celestial Handbook," a 3-volume library that is packed with much information of all 88 constellations and the objects contained within them. Look for Orion as the final "chapter" in Book Two of Burnham's.
This Guide - PART III - will comprise the in-depth version of our typical "GO TO" TOUR Constellation Guide's Concise Directory of objects for your computerized telescope and discusses the remaining (but certainly not less interesting nor exciting) objects within Orion, including the "Horsehead Nebula" (IC 434), many other reflection nebulae, a great selection of galactic clusters visible in telescopes of all sizes and several of the hundreds of spectacular double and multiple stars held within the Hunter's haven.
For the full listing of all brighter stars (to naked eye limit) which includes: 1) Bayer; 2) Flamsteed; 3) SAO #; 4) R.A. & DEC; 5) brightness; 6) most notable double and multiple stars; 7) variable star designations; I encourage you to visit the wonderful Constellation reference site by Englishman Robin Gatter at: http://www.gatter.demon.co.uk/data/Ori.htm as well as all other constellation Star Tables that he has provided through this wonderful web site. This is a great reference to print and put into a binder for cross referencing star designations, locating double and variable stars, and current coordinates in the sky.
As with every "GO TO" TOUR guide, each GO TO object in Orion is discussed for your telescope regarding the type of conditions necessary for you to view it optimally for discern the very faintest details.........magnifications and aperture necessary for most objects, and much, much more. This is YOUR complete GUIDE to get you on your way to exploring the best (and few!) objects in these two constellations. The following listing of "BEST" objects contains the finest or most interesting from my own observing experience and preference.
Use the 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.
For a VERY complete listing of NGC objects that are found within Orion, you may access: http://www.gatter.demon.co.uk/data/OriN.htm which will provide a complete listing of all suitable NGC objects, their coordinates, magnitudes and various reference and cross-reference material for each object.
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!
YOUR ORION CONCISE DIRECTORY OF INTERESTING OBJECTS -
In addition to our regular listing of a few selected objects, I have included the complete abstract listing for the ten (10) nice galactic star clusters that are viewable in this constellation via modest instruments; that listing will be found at the end of this concise description of our TOUR.
For our visit into lair of the great Hunter, I have chosen the finest (or most interesting) 11 objects in this ORION "GO TO" TOUR (as with all GUIDES, all objects listed below will be visible in most 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 for FINDING the objects initially. Indeed, I strongly encourage you first FIND the target object, or its approximate location through your GO TO function with your lowest power and then - once IDENTIFIED positively - move up slowly in steps with magnification if necessary. Remember, not all objects "like" magnification. Sometimes better "field of view" (such as the wonderful wide fields provided by the ETX 60 and 70) is desired over light gathering (like the big LX 90) and magnification.
The rule for determining "optimum magnification" is that: 1) too low power results in sky background glow detracting or diminishing the contrast against the deep sky object; 2) too high magnification darkens BOTH the sky background AND the object; 3) medium magnification can be achieved at which you have MAXIMUM contrast between the object and its darkened background sky. I have found through three decades of direct observing that about 15x per inch aperture (36x for the ETX 60/70; 55x for the ETX 90; 75x for the ETX 125; and, 125x for the LX 90).for deep sky observing is PERFECT for most objects. That being said, always remember that DOUBLE or multiple stars require whatever power you can crank out....the seeing conditions are the limiting factor here. For a complete discussion on magnification and how it applies to YOUR telescope, visit my review at: http://www.weasner.com/etx/buyer-newuser-tips/tp_magnification.html
For my complete and comprehensive discussion regarding seeing conditions and sky transparency, see: http://www.weasner.com/etx/buyer-newuser-tips/seeing.html .
With all deep sky objects, avoid attempting to observe when the moon is in the sky, even a very thin crescent, as its brightness in the sky will overshadow the very dim contrast afforded by even the brightest deep sky object; if you see the object at all against moonlight, you will NOT see the subtle outlying areas or the full detail of what is presented. Be sure to refer back to Part II - "Orion Nebula" of this three-part GO TO series regarding the dark adapted eye and its importance when viewing the great expanse of diffuse emission nebulae within this constellation.
Also, as I always suggest with all of the "GO TO" TOUR constellation lists, 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. For multiple stars and many listings of the finest deep sky objects, the classic work, Burnham's Celestial Handbook, Vol. Two is highly recommended.
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 ORION; you may wish to find the majority of the objects from the AutoStar Library (for example, you can easily go to the beautiful ORION NEBULA (Messier 42) if you pull up "Object/Deep Sky/Messier/..then type in '42'...." and then press "Enter", followed by "GO TO" to access this very delicately star-laced gem. On the other hand, if you want to experiment and become a "better AutoStar user" try entering the exact R.A. and DEC coordinates (given in EPOCH 2000 coordinates in the listing below) of that same object as described by 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!
Of course, another method of Autostar acquisition of the Great Nebula is to go to the deep sky named objects by: SETUP / OBJECT / DEEP SKY / NAMED...and scroll until you see "Orion Nebula." At that point press Enter which will bring up much data and information about this glorious object if you keep scrolling....however to access the object via automatic GO TO, simply press "GO TO" on the key pad at which time the telescope will take off for Messier 42.
Yet again, you can use the handy "NGC OBJECT" component of your Autostar library. In addition to the designation "M42", this object has the label NGC 1976. On Autostar, key in SELECT / OBJECT / DEEP SKY / [scroll to: "NGC" and press "enter"]; now merely key in the number "1976" and press enter to activate the Autostar on this object...continuing to press "Enter" will allow handy information about this object to be displayed on your keypad....merely press "GO TO" to move the telescope to the Orion Nebula.
You will access your FIRST GO TO target - (usually the alpha star in each constellation) - via the command "SETUP / OBJECT / STAR / NAMED....and scroll to "Betelgeuse" then press "Enter" and subsequently "GO TO" to move your this bright red supergiant star. Remember also that many distinctive objects are sometimes listed among the "named" objects. So, likewise for that object you might merely go to SETUP/OBJECT/DEEP SKY/NAMED....and then scroll alphabetically to the "common" name of the object if you are not already there; press "enter" and then GO TO and your scope is off and running! For Auriga, there are NO objects other than the brighter stars that are listed as common "named" objects in the Autostar library by name.
You may also access the constellation by: SETUP/OBJECT/CONSTELLATION/"Orion".....Enter....GO TO, which will take you close to the central position of the constellation's boundaries.
The Concise List (featuring Epoch 2000 coordinates)
OBJECT 1: bright star - BETELGEUSE (alpha Orionis) - R.A. 05h 55' / DEC +07 24 - Mag. 0.7 - Brilliant red supergiant OBJECT 2: bright star/double - RIGEL (beta Orionis) - R.A. 05h 15' / DEC -08 12 - Mags: 0.3 & 6.7, wonderful double star! OBJECT 3: quad star - HEKA (lambda Ori) - R.A. 05h 35' / DEC +09 56 - Mags: 3.4, 5.6, 11 & 11.5 - Can you see all four?? OBJECT 4: a double/triple? - MINTAKA (delta Ori) - R.A. 05h 32' / DEC -00 18 - Mags: 2, 6.5 & 14 - #1and 2 easy...#3 tough! OBJECT 5: test double - eta Orionis - R.A. 05h 25' / DEC -02 23 - Mags: 4 & 5 - test for 3", only 1.5" space - nice star! OBJECT 6: nice easy double - rho Orionis - R.A. 05h 20' / DEC + 02 51 - Mags: 4.5 & 8.5 - good double for 3" and up! OBJECT 7: test double - 14 Ori - R.A. 05h 08' / DEC + 08 30 - very tough for 5"; not easy in 8" scope! OBJECT 8: variable star - W Ori - R.A. 05h 05' / DEC +01 11 - easy semi-regular, ranges from 6.5 to >10 in about 210 days OBJECT 9: planetary nebula - ngc2002 - R.A. 05h 39' / DEC + 09 04 - Mag: 12.0 w/ 14th mag. star - very tough, 8" or above OBJECT 10: galactic cluster - ngc2112 - R.A. 05h 54' / DEC + 00 24 - Mag: 8.6, about 90 faint stars - fairly large OBJECT 11: galactic cluster - ngc2141 - R.A. 06h 03' / DEC + 10 26 - Mag. 10.8, 100 stars (fine in 5" and up!) OBJECT 12: galactic clusters - ngc2169 & ngc2194 - R.A. 06h 09' / DEC + 13 57 - Mag. 6.4 / 9.2 - tiny clusters with about 18 / 100 stars...cool! OBJECT 13: galactic cluster - ngc2186 - R.A. 06h 12' / DEC + 05 26 - Mag. 9.3 - very small w/30 stars. Good in 5" + OBJECT 14: diffuse nebula - Messier 78 (ngc2068) - R.A. 05h 47' / DEC + 00 03 - Mag. 10.3 - looks like small comet! OBJECT 15: ORION NEBULA - Messier 42 & 43 (ngc1976 & 1982) - R.A. 05h 35' / DEC -05 23 - details in Part II OBJECT 16: "horsehead nebula" - IC434 - R.A. 05h 41' / DEC -02 25 - very faint, seen only in wide field optics and dark skies
A VISUAL GUIDE TO OUR DEEP SKY OBJECTS IN ORION
Object 1 - Our "Starting" Bright Star - "BETELGEUSE" (alpha Orionis - see Part 1 for pronunciation!)
Throughout the "GO TO" TOUR Constellation Guides we have discussed the beauty and many times symbolic meanings of the Arabic names which most of our bright stars still retain today. We have "Aldebaran" as the "eye of the bull," "Deneb" signifying the "hen's tail," and now we have the difficult-to-pronounce BETELGEUSE....the "armpit of the giant," from the romantic Arabic "Beit al-geuze." Not the most alluring nor creative name, but nonetheless straight and to the point. Betelgeuse is NOT always the brightest star in Orion, that distinction belonging to bright white Rigel to its southwest. As a red supergiant however, the star is quite variable and is the brightest of all known variable stars. Thus, many times Betelgeuse can reach "0" magnitude, or slightly brighter than Rigel....other times it fades to depths fainter than magnitude 1.5. This incredible star - located only 540 light years distant has a volume exceeding - are you ready for this? - 160 MILLION TIMES our own sun. Because of its tremendous size and proximity, Betelgeuse can actually show in the world's largest telescopes, a "disk", rather than a point of light for its surface rather than a point of light like all other stars. This is an incredibly interesting star for further reading and I strongly encourage those not familiar with the evolution of stars to take the time to learn more. Recommended reading is the classic work, "Red Giants and White Dwarfs" by Robert Jastrow.
Object 2 - Another "Brightest Star" - the beautiful double star RIGEL (beta Orionis)
Because of Betelgeuse's variability, I suppose we would slight the equally-bright RIGEL, the beta star in Orion, if we did not give it top billing along with the giant's armpit star. Not much more creative, the name is also from the Arabic "Rijl Jauzah al Usra" with only the "Rijl" part remaining in recent times. Nonetheless the long form of the name tells us that this star is "the left leg of the giant man." Rigel is nearly twice as far as Betelgeuse, and like it red counterpart, is also a supergiant star....only a brilliant white one, with an incredible luminosity 57,000 times the output of the sun. During your next winter or early spring star party, let your visitors thrill at just how bright that actually is: if we could move Rigel to the distance of many of our closest stars - like our brightest star in the sky, Sirius - it would be only slightly dimmer than the full moon! Other than shining like a sparkling diamond in very low power views near the winter Milky Way, Rigel is best known as one of the prettiest double stars for amateur telescopes. Almost due south of the brilliant magnitude 0.3 star is a much fainter 6.7 magnitude star that "should" be easily seen in the smallest of telescopes...IF the brightness and distance of 9" arc were the only factors. However, I have found the companion VERY difficult in a good 4" refracting telescope because of the glare of Rigel itself. The fainter star contrasts wonderfully in larger telescopes. In an 8" or 10" glass the brilliant white coloration of Rigel makes an outstanding comparison for the true blue color if its companion star. In Part I the Orion association of stars was discussed, noting that many of the brightest stars of the constellation were actually a part of a very large "clustered grouping"; Rigel is certainly though to be one of these many gravitationally-bound stars, although it appears to be slightly closer to us than the 1,200 to 1,500 light years for the remaining Orion association stars.
Object 3 - Beautiful Double Star - HEKA (lambda Orionis) - that you can turn into a Quadruple star!
Pronounced "hee-KAH", this is a well known double star and beautiful double star, the primary being magnitude 4.2 and the secondary, exactly northeast from the brighter on (Position Angle 44 degrees), is magnitude 6.1. Separated by 4.5" arc, this is an excellent object for even the smallest telescopes. There should be no mistaking this star when you " GO TO" it....it is the brightest of three stars that comprise the "head of the giant", the other two being phi-1 and phi-2 both of which are about 4th magnitude.
However, observers with a 4" telescope and more ideally and 8" and larger will realize double the fun on this star as there are also two ADDITIONAL stars with respect to Heka, both faint in the magnitude-11 range. The "C" star (see diagram above) is almost exactly due south of Heka by nearly 30" arc and is slightly brighter than its other twin, magnitude 11.5 and located slightly more than TWICE that distance from Heka and almost exactly due WEST (Position Angle 271 degrees). Use medium-high magnification (about 20x per inch aperture) or more to reveal these fainter stars. The 4" and 5" telescopes will be pushing the limit to glimpse these very faint objects, but under good dark and steady skies they should be "reachable." This quad makes a very pretty sight in an 8" scope at about 160x.
Object 4 - Another Good Double - MINTAKA (delta Orionis) - Here is one for everyone!....easy to find and just as easy to see!
Here is one that does not require a lot of grunting and groaning to locate. Delta Orionis, "Mintaka" at magnitude 2.2 is the fourth brightest star in Orion and forms the westernmost "belt star" (See Part II) of the Giant's garments. In addition to being an easy double star target for almost every telescope, this is also a variable star for the keen eyed observer who wants to watch it brighten and dim every 5.7435 days. Its magnitude variation is about 0.2 from maximum to minimum so it is just detectable to the human eye without error as to when it is brightest and dimmest....you can use the other nearby stars (see the list in Part II) as a judge of its brightness night-to-night.
However, Mintaka is best known as a beautiful and easy double star. Being part of the "Orion Association" (Part I), Delta Orionis is - like all the others - part of a group of very young energetic white stars, some 1,500 light years distant. Its companion is also a very white star so do not expect any color contrast in this pair....the brightness contrast will be enough to get you excited. Look for Mintaka's fainter 6.7 magnitude companion almost due north of the bright star, almost 1 minute arc, or slightly greater than the planet Jupiter would extend in your eyepiece. There will be no mistaking the companion as it will be the brightest of the many stars that you are likely to see in this beautiful low power field of view. Use about 10x per inch maximum to appreciate the star-rich field.
Object 5 - Another double star - A good test star for the 3" and 4" scopes! Eta Orionis
With so many other bright stars nearby it is a wonder that Eta Orionis, magnitude 3.3 did not get named. For it is the one star that actually "boxes in" the belt stars at a right angle giving the grouping a confusing "dipper shape." Nonetheless, this is the fairly bright whitish star that is directly south of Mintaka (see above) and west of the "sword grouping" which includes the Orion Nebula. This star is really not as easy as its 1.4" separation indicates. The following listing:
2.5" inches = 1.81" arc
3.0" = 1.51
3.5" = 1.30
4.0" = 1.13
Shows what separations should be attained in good telescopes of smaller aperture. Thus, it appears that the ETX 90 should resolve it (barely) and it should be a cake walk with the ETX 105; however, this is not the case; on a very unsteady night recently I noted that - in an 8" Schmidt-Cassegrain - it could easily have been overlooked as a double from the blurring of the two Airy disks from bad seeing. Use pretty high magnification (about 20x per inch minimum) to get the most out of your telescope on this star. On a very steady night I encourage you to increase the power to about 35x or 40x and note the distinct "purplish" color of the fainter 5.2 magnitude star which is now nearly due north of the Eta Orionis.
Object 6 - Now....here is one for the 3" scopes! Double Star Burnham 1053
Once again, you will access this star either by using the R.A. and DEC manually entered via the hand controller, or by the "old fashioned" setting circles on your scope (they actually work very well....and it's fun!). Burnham 1053 is a very close star for the 3" to 5" size range, separated by 1.4" arc, right at the Dawe's limit for the 3" scope. The primary "A" star is magnitude 7.5, so it is not the brightest of our Auriga objects by a long shot. Center that yellowish star and increase the magnification to about 200x and look for a faint 9.6 magnitude star near DUE NORTH (a bit to the west) and very close. You will require a very steady night and very high magnification (take it on up if the air will hold it!) in the smaller of the two scopes.
Object 7 - Another Good Double for Smaller Telescopes - Rho Orionis
This is yet another double star that will be a great target for smaller telescopes, but is an excellent double for all. Rho Orionis, magnitude 4.6 is imagined to be part of the left arm of Orion supporting the shield of animal skin or bow, whichever you chose to see as the Giant's weapon of choice. It is easy to locate in the telescope and once found, look for its companion to be just north of due east in the medium power field of view; I recommend about 15x per inch to adequately show the magnitude 8.6 secondary star....be sure and use a bit more magnification once found and look for the distinct blood-red colors of these two stars! With a separation of 7" arc, this should be an easy target with a 3" and a beautiful sight for its color in 5" and larger telescopes.
Object 8 - The Semi-regular Variable Star "W ORIONIS" - Excellent for all telescopes!
This is an EXCELLENT variable star for all telescopes, but exceptionally so for smaller instruments, since rarely are there "semi-regular variables" with a magnitude range through their entire maximum-to-minimum cycles that remain bright enough for continuous observations with smaller instruments. For a discussion on variables, and the importance of regular monitoring of unpredictable ones, see my complete discussion of variables and observing techniques at: http://www.weasner.com/etx/ref_guides/variable_stars.html . W Orionis varies somewhat periodically at a rate of "maybe" 210 days; but the cycle is marked and interrupted occasionally by small "jitters", jumps and declines in magnitude and periods when no change takes place at all. Semi-regular stars, although thought to essentially be pulsating Mira-type stars, are not completely understood as to why their variations are not entirely predictable. Thus, YOUR observations of them are vitally needed over a long period of time. Indeed, with this star ranging in magnitude from a bright 6.4 to fainter than 10.5, you can compile your own light curve after only less than a year, giving details and a visual history of the erratic variations - as well as its regular cycle.
As with all variable star observing, the ideal source for information, comparison star charts, and to report YOUR valuable observations (badly needed on these irregular stars, by the way!), is the American Association of Variable Star Observers (AAVSO - www.aavso.org) in Cambridge, Mass. The charts for nearly every variable star - as well as "new stars" (such as novae, and stars not previously known to be variable) that appear from time to time - can be downloaded off the internet into a file in your computer; save the file and bring it up.....the image will be huge. Resize this image to fit your page, resave, and then print for a good chart to use at the telescope!
To make estimates on this semi-regular variable, use the AAVSO "a/b" chart found at: charts.aavso.org/standard/ORI/W_ORI/WORI-AB.GIF. This is the wide field finder-type chart which features brighter stars over a larger area of sky from which to pick given comparison stars. Also, note that this is the AAVSO "standard" chart and not the "reversed chart"; the reversed editions of the charts are newer and are matched to the reversed field of view of the Maksutov and Schmidt Cassegrain telescopes, which result from the diagonal prism or mirror.
Object 9 - A Faint Planetary Nebula - NGC 2022
Here is an object that is definitely for "the faint at heart." Located just east of the "head of Orion" star HEKA, this rather large (28" arc...about the diameter of Saturn's globe in your eyepiece!) gaseous remains of a stellar explosion is ONLY magnitude 12.4....remember that is not "stellar" magnitude but rather the magnitude of such a star if spread out over this rather large 28" arc. Thus: very faint indeed. However, based on my actual observations of this object, it IS visible in the 8" aperture telescope and becoming increasingly more interesting in larger instruments. On a very dark night a really well-collimated 8" or 10" telescope might reveal the faint 14.6 magnitude central star to this very elusive planetary nebula. NGC 2022 is one of only two - and is the brightest of - planetary nebulae in the entire constellation of Orion...a constellation virtually FILLED with other nebulae: reflection and emission, but only two faint planetary nebulae!
Object 10 - A Nice, Often Overlooked Galactic Star Cluster - NGC 2112
NGC 2112, at magnitude 8.6 and containing about 90 to 100 very faint (10th to 12th magnitude) stars, is an often ignored object in Orion in lieu of the many fascinating nebulae that pack this constellation. This galactic star cluster, spread over a relatively small 12' arc circular area, is located almost due east of Mintaka, and makes a fairly even triangle with that star in the western end of Orion's "belt" and Alnitak, the easternmost belt star which is southwest of NGC 2112. Very low power instruments may be able to actually get Messier 78 (discussed below) and this cluster in the same field of view, since NGC 2112 is only a few degrees due east of M-78. This cluster is clearly visible as a faint circular patch of light in smaller instruments at medium magnifications (about 15x to 20x per inch aperture). However, with the 4" and larger telescopes more and more stars are visible; look for a glowing circle with about 25 or 30 stars in a good 4" scope on a dark night, while the 8" should reveal some 80 of the brightest stars.
Object 11 - Another Nice Galactic Cluster, NGC 2141
Although fainter (magnitude 10.6) than ngc2112 discussed above, this is a cluster that should be visible in most telescopes. In smaller instruments this object appears similar to NGC 2112, with no particular detail other than a faint smudge of light, though dimmer, of about similar size to that of ngc2112. The 4" telescope will likely not be able to see any individual stars in this cluster as the brightest are about magnitude 11.8 at best. However a 5" or 6" telescope will begin to reveal some "glittering" among the nebulous appearing background, while the 8" should reveal perhaps half of the nearly 100 faint stars packed into this cluster.
OBJECT 12 - A Brighter (albeit smaller and less impressive!) Galactic Cluster - NGC 2169 (and NGC 2194)
This tiny star cluster (only 5' arc!) is located in the same wide field view as the brighter star "xi Orionis" which marks the base star of Orion's "club". Since this location is amidst the wonderful winter Milky Way, rich with faint stars throughout nearly every telescopic field of view, this is a place to let your telescope - and your imagination - wander through the star-drenched blackness of winter's night. NGC 2169 contains only 18 stars, but all are bright enough to discern in the 3" scope, and this smaller aperture is perhaps providing the best view of this spectacular area....not so much because of this fairly sparse cluster...but more so because of the proximity to xi (magnitude 4.48) and the many stars that are visible in all apertures throughout this region. It perhaps more than anything else will serve as a benchmark for your further random explorations throughout this very beautiful area of sky, sweeping southeastward into the rich Milky Way and nebulae of Monoceros. In larger telescopes (5" and up), observers should sweep from ngc2169 only about 2 degrees southeast to find another nice cluster, and one more rewarding to larger apertures: NGC 2194. This is a very star-rich cluster of magnitude 9.4, containing at least 100 stars packed into a VERY small circular area only 8' arc across! At first this resembles a very sparse globular cluster, but the 8" and larger telescopes will begin to show the even scattering of this galactic star cluster.
OBJECT 13 - Yet Another Galactic Cluster - NGC 2186
Located smack-dab in the middle of Orion, very close to its eastern border with Monoceros is an isolated galactic star cluster, ngc2182. It is about 5 degrees east and a bit to the south of bright red Betelgeuse. This cluster is right on the western edge of the winter Milky Way, and hence provides some spectacular viewing of very faint stars limited in the field only by the size of the telescope you are using. NGC 2186 is tiny (5' arc) and has only 30 stars, magnitude 10-11, but is a brighter 9.3 magnitude overall and clearly distinguishable in the 3" and 4" telescopes, appearing like a very small unresolved faint planetary nebula or globular. The 5" and 8" scopes will begin to reveal many of the stars, and the larger the telescope, the better the view. With all telescopes use medium-high (20x per inch aperture) to view this faint and small object.
OBJECT 14 - A Nice Diffuse Nebula - Messier 78 - (this is the kind of object that kept confusing Messier as "comets!")
Messier 78 is an interesting object in the 4" telescope and up, and certainly can be viewed with a 3" but with lesser detail. Its overall brightness is very faint (10.3) when you consider that it is spread out over an extended 8' x 6' field of sky. This is a very difficult object visually, but does have its merits. This object has been more confused as a "comet with a double nucleus" than any other object in the sky! Like the Great Orion Nebula, M-78 has gases that are visible to us because they actually glow....not reflect. There are two very active white stars embedded within this diffuse nebula, both about magnitude 10.2 and thus better seen in telescopes 4" and up. These two "equal" stars are arranged in a nearly north-south orientation some 53" arc apart. They become quite clear in the 5" scope and a bit of nebular detail becomes visible as you move up in aperture to the 8" and larger telescopes. With larger telescopes, look for Messier 78 to be somewhat "comet-shaped," in that one end of it (the northwest end) is very blunt like a small comet's head, and the other (southeast) end appearing very diffuse and simply "disappearing into darkness" much like an outstretched comet's tail. This is a very interesting object to study under medium (about 20x per inch aperture) magnifications in telescopes of any size; the longer you look at it under very dark skies, the more you begin to actually see of it! Like most of the stars and most of the nebulae in Orion, all of this is somewhat interconnected at a distance of some 1,500 light years, give or take a few parsecs. The two embedded stars and the spectacular nature of this "little brother" to the Orion Nebula is well captured in the following photograph as captured in the 2MASS sky project cameras.
OBJECTS 15 - Messiers 42 and 43 - The Great Orion Nebula (and his sidekick)
For a complete discussion of the Great Orion Nebula and the fantastic area surrounding it in the constellation of Orion, refer to my Part II of this three part Orion "GO TO" TOUR. Messier 42 and its associated stars of theta Orionis (the "trapezium") comprise the central star of Orion's "sword," while Messier 43 is a faint path of displaced nebulosity and bright stars immediately NORTH of the Orion Nebula. The two comprise a spectacular sight on a dark winter's night at the lowest power you can muster in any telescope. Seen also in Part II, the classic beauty of the 100" Lick Observatory's portrait is reprinted here so that the smaller area of M-43 is NOT confused for NGC 1977, which is the brighter diffuse cloud seen at the bottom (North) of the photo. Messier 43 is the small cloud immediately below the "fish's mouth" in this photo and almost touching the huge M-42. Note the bright star Iota (HATYSA....see Part II) at the top (South) of the Orion Nebula. Below this photograph is the Lowell Observatory's 42-inch telescope's image of a close-up of Messier 43 (this image - of M-43 - is reversed from that of Lick Observatory's, with NORTH up and EAST to the right, as seen in a Maksutov or Schmidt-Cassegrain telescope).
OBJECT 16 - The Famous HORSEHEAD NEBULA - IC 434
I distinctly remember about 25 years ago during a major dark sky public observing event one of the local astronomy club member's comments. He had just gotten a new 8" Newtonian telescope from Criterion, a "Discovery" I think it was. This young and energetic man was full of the energy that all of us feel when getting such a new and - in 1975 a BIG - telescope. It was a very cold early November event to coincide with the Leonid Meteor shower which would hit shortly after midnight when Orion would be high in the sky. Never having used the telescope in so dark a sky as we had on Petit Jean Mountain, one would assume that one of his first major targets would be the Great Orion Nebula. Not so.
"I'm going to see the Horsehead!" he proudly proclaimed, patting the less-than-shiny white tube of the new telescope. "Finally going to see it!", stroking it like the fur on the back of a cat's neck. He, of course was referring to the famous "Horsehead Nebula" just south of Zeta Orionis, an object astronomers refer to as "IC434." Actually, this object is as large as two moon diameters and is magnitude 1.9! Why SHOULDN'T he expect to see this most famous of dark and bright nebulae combined in the shape of a horse's head?
"In that?" I asked with reservation. He looked proudly at the Criterion.
"Yep...it's an 8-INCH!" Much exclamation put on that point, and I did not have the heart to tell him he could have had a 20" right then - actually more like 3 a.m. - and still would be unable to see the object. But sometimes practical experience is the best teacher, albeit most of the time a disappointing lesson. But his reasoning was quite good. He was moving up from a 4" refractor with considerably less light gathering and from a darker-imaging f/15 focal ratio to a fast f/6 in the Newtonian and a brand new 25mm Kellner eyepiece. The object is BIG and it is BRIGHT. The following photograph demonstrates how distinct the Horsehead is photographically, with Zeta brightly shining above (north) of it.
However, much to his tremendous disappointment he search and searched the area, using a very carefully plotted "map" of the field stars I have prepared for the group ahead of time. Using these stars from any good star program or atlas, you can easily plot where it "should be" just like extrapolating where you are on a map in relation to two towns on any highway.
"I THINK I might see it..." he would continue to shout over the rest of the group, now huddled around a small 5" Jaegers lens f/5 refractor using about 15x. In this small, short and very much NOT impressive little scope here was the Horsehead, very faintly but clearly distinguishable. No mistake about it in the nearly 3 degree field of view, right where it should be due south of Zeta and a bit of a right angle to Sigma Orionis to its west. The intrusion of "Barnard 33", a very dark nebula that light cannot pass through over IC 434 (the bright nebula behind it) was an impressive yet very ghostly and vague image. Then the gentleman with his homemade octagonal wooden-tube 4-1/4" f/4 hand held richest field telescope likewise spotted the Horsehead.
Meanwhile, back at the 8" it continued. "Is it RIGHT or LEFT of that star?" we could hear him ask, still not convinced that he was seeing it....I could sense disappointment setting in quickly. He was not going to see the Horsehead Nebula in that telescope.
Very low and wide field instruments are required to visually detect IC 434 and Bernard's dark nebula 33. Indeed, it can even be glimpsed in the large 11x80 and 20x80 binocular if one can hold them steady enough; I have seen it this fall in early morning skies from the mountain in an ETX 70 with a 26mm Plossl eyepiece! But I cannot see it in the ETX 125, nor in the LX 90 and certainly NOT in the 12" and larger telescopes. For the Horsehead, one needs:
1) the very darkest skies;
2) good low power optics with excellent dark sky contrast;
3) the Horsehead to be as high in the sky as possible;
4) totally dark-adapted eyes;
5) wide field of view; and,
6) a good finder chart printed from one of the PX sky programs to identify exactly where it should be located relative to stars that will be seen in wide angle views.
The Hubble Space Telescope has no problem "seeing" this object, and it is relatively easy to photograph, even by piggybacking a camera with a telephoto lens and exposures of 10 minutes or greater on fairly fast (ASA 400+) film. (see my complete discussion on getting started in piggyback astrophotography at this web site via: http://www.weasner.com/etx/ref_guides/astrophotography.html . The image of the Horsehead Nebula from the Hubble below clearly shows the dark Barnard 33 nebula as it overrides the bright nebula behind it, offering a somewhat "3-D" impression of this remarkable object.
There are actually two (2) components to the Horsehead Nebula. First is the bright emission nebulae that fills the sky between Zeta and Sigma Orionis, running almost perfectly north-to-south. This nebula is known as "IC 434" and is an incredible 60' arc (one degree!) long north to south (that is the length of two full moons edge-to-edge) and 10' east-west. It is believed that the illumination of IC 434 is from the energy of the star Zeta, much like Theta Orionis activates the glowing of the Orion Nebula (see Part II). Although it appears as if the nebulosity just "stops" abruptly at its eastern edge in the photographs above, it actually is still there, merely covered up by the dark nebulae that also makes up the famous Horsehead, or dark nebula B-33. Indeed, you will note, even if you do NOT see the Horsehead, that there is a sudden "absence of stars" to the east of a one degree imaginary line running south from Zeta Orionis....the stars are there....they are just covered up by light absorbing dark interstellar matter, the very stuff that covers up the bright nebula behind it to create the effect we know as "the Horsehead." Look at the photograph above and imagine it in 3-D....the dark nebulae is closest to you, while the bright cloud of gas is behind it. Imagine it as fog filling in rapidly on a cold spot on an English moor.
My friend would not be too disappointed if he knew that the Horsehead is NOT visible in the world's largest refractor telescope visually either! Indeed, the larger the aperture and more "powerful" the telescope, the less likely one is to actually glimpse this object with the eye. Using the criteria listed above, your chances are best for spotting the nebula, but also knowing where to look is a much benefit. I mentioned the small charts that I had circulated to assist observers in locating the Horsehead. A sample of that is shown below,and you can click and print this chart for use at the telescope. NOTE: for this chart, I have reversed the field so that it will appear as in a Maksutov or Schmidt-Cassegrain, with North at the top and EAST at the right, a mirror image of the way the sky actually would appear!
Note the two faint stars embedded within the brighter IC 434 just to the west of the Horsehead and also the brighter star SIGMA ORI (discussed as our "User Object" for Orion, below). Drawing an imaginary line eastward from bright Sigma through the faint star marked with the ARROW, you will find the Horsehead an equal distance on the other side of that fainter star than it is from Sigma. Also note another method of finding the Horsehead using these stars. The nebula makes a right angle almost perfectly between Zeta and Sigma, due south of Zeta and nearly due east of Sigma.
While in this area, note the two emission nebulae NGC 2023 and IC 432, both of which are far easier objects than is the Horsehead. A good 4" scope at very low magnification will show both of these as a medium-brightness star surrounded by a "halo" of light....very nice objects to add to your list of exotic targets! For larger telescopes and equally rewarding object is IC 431, just to the west and slightly north of IC 432. Merely "star-step" your way through this exciting region of Zeta Orionis and see how full of wonderful objects and star groupings it truly is!
Just as so much within the mighty borders of Orion the Hunter, the Horsehead (B-33 and IC434 combined) is some 1600 light years distant, and thus is part of the huge association of bright white energetic stars and emission nebulae that comprise this wonderful region of our visible universe.
WANDERING ABOUT....YOUR NEW "USER OBJECT" IN ORION
Just southwest of Zeta Orionis and nearly due west of the Horsehead (see the finder chart above) is a wonderful multiple star for moderate-sized amateur telescopes, SIGMA ORIONIS. This star has a combined magnitude of 3.7 and a "total" of five stars in a very complex multiple star system. The brightest of these is the 4th magnitude "A" star, like nearly all other stars of the Orion Association a very hot energetic white star in the 1,400 to 1,500 light year distance range. Using the chart below, let us look at this complicated orrery of stars. The star "B" is a 5.9 magnitude white star as well, but this star will likely not be seen in amateur telescopes. At only about 0.3" distance away in Position Angle 200 degrees (just west of due south from the brightest star), it is theoretically visible in a good 16" under good conditions, but typically cannot be split into two stars. Only on extremely steady nights and magnifications approaching 800x to 1,000x have I ever seen this star in the 24" Cassegrain. But.....there's more!
Look for the 7.3 magnitude "C" star in Position Angle 84 degrees, or nearly due WEST of the bright unresolvable pair A-B; it is bright enough and far enough away (13" arc) that it should be an easy object in all telescopes at medium power (about 15x per inch in most cases). About the same distance away, but nearly opposite the brighter Sigma is star "D", which is much fainter at magnitude 10.2 and 11" arc distant. A fifth star (making FOUR that can be seen with amateur telescopes) is much brighter and easy to spot in the smallest of telescopes, this "E" component being a 6.4 magnitude star at Position Angle 61 degrees, or rather northeast of the bright primary star(s).
This is a wonderful object to add your growing "User Object" library for the Autostar and is a fine multiple star that is not included on the Autostar or Nexstar list of double/multiple stars. Its epoch 2000 coordinates can be entered as: R.A. 05h 38.7m / DEC (-) 02 36.
On AutoStar, go to: "Select/Object [enter]...." scroll down to "User Object" [ enter]. Now enter the coordinates given above for "Sig Ori", 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 "3"[Enter].
With the addition of this star, you now have a wonderful and relatively complicated multiple star in the collection of celestial curiosities for your next star party or family outing with the telescope!
P. Clay Sherrod
Arkansas Sky Observatory
Conway / Petit Jean Mountain
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