![[Home!]](../images/mighty_etx.jpg){kind=small}
CONSTELLATION GUIDE
Last updated: 21 October 2001
|
CONSTELLATION GUIDE |
"GO TO"....ERIDANUS
....among the sky's bright and beautiful stars: "A River Runs Through It"
From: sherrodc@ipa.net (Clay Sherrod)
As our "GO TO" TOUR Constellation Guides take us even so deeper into the rich and clear winter skies of the northern hemisphere, we embark on a float trip down the Celestial River ERIDANUS in our 31st installment. It is appropriate as we approach the half-way point in these TOURS that we have discovered the "source" of so much watery references throughout our fiction-filled firmament. In this watery abyss that is space, we find a sea monster or whale (Cetus), and a Dolphin (Delphinus), not to mention both a large and small water snake (Hydra and Hydrus), the leaping swordfish (Volans), a guy carrying water around (Aquarius), a ship's sail (Vela), apparently a fishing net that got lost from the same boat (Reticulum), along with their compass...no wonder they lost their ship! (Pyxis), a northern fish (Pisces) and southern fish (Pisces Austrinus), a water crane (Grus), a swan in flight over the water (Cygnus), yet ANOTHER compass (Circinus), the water crab (Cancer), and - oh my goodness, we've found the keel from the Argonaut's ship! (Carina) and of all things.....a SEA GOAT! (Capricorn).
This is not to mention the scores of star names from both north and south celestial hemispheres that were aptly named for or about the oceans, sea myths and mythology, water and water-related creatures. So WHERE does all this stuff reside? Where is the remains of the tattered and torn vessel of the famed Argonauts....the home of the sea monster, and for gosh sakes WHERE does a Sea Goat live?
Why... in Eridanus, of course! Curiously since this constellation is a vague and sprawling with few spectacular and eye-catching asterisms, this was actually one of the 48 original constellations assigned by Ptolemy in the second century A.D. From Egyptian influence perhaps more than 2,000 years before him, Ptolemy cast honor up this meandering stream of stars to represent the great river in which the unfortunate Phaethon plunged to his steamy death. After learning that his father was a great god (Helios, the sun god), Phaethon (a mere mortal) begged his father ("Daddy....Puuullllease!!??") to allow him one morning the great honor of driving the fiery chariot of the sun across the sky from east to west to bring great heat and light to the mortals below on Earth ("Please, Daddy....PLEASE?!"). Begrudgingly Helios finally gave in like all fathers and allowed the ill-fated day to begin with Phaethon and his flaming cargo rising as predicted in the east and begin its path across the sky....but unfortunately VERY recklessly (something here about a "teenage driver," but it was lost in the translations). Soon, Phaethon lost control of the mighty chariot and sure enough it began careening out of control, surely to whack the Earth in a fiery fireball of doom.
Since Zeus (as we have seen) had many love interests in the beautiful mortal women of Earth, he could not allow such a catastrophe to lay waste his harem and thus, cast a huge thunderbolt upon the descending Phaethon and his chariot, sending in plummeting instead into the perpetual River Eridanus, which steam perpetually (the Milky Way) from the now-extinguished sun. The story does not say anything about WHERE Helios was able to find another sun in time for sunrise the NEXT morning, but I have it on good authority that Wal Mart was having a "Sun-day" sale.
The steaming mists from this still simmering sun fill the winter skies even today, as the rich winter Milky Way to the east of River Eridanus carries the clouds far to the north, through Orion, Taurus, Auriga, Perseus and Cassiopeia.
It is interesting to me that even the constellation CYGNUS, the swan of summer skies (also in the Milky Way) originated in this story as well.....it so happens that a very devout friend of Phatheon, seeing his plight as he plunged into Eridanus, dove in after him in an ill-fated attempt to rescue the young man. He drowned and showing compassion for so great and trusted friendship, Zeus changed the lifeless body of his would-be rescuer into the form a beautiful swan to fly above the river of the sky for all eternity.
This tale did NOT originate in ancient Greece, however, even though that is how we remember it best. The legend of the sun-toting chariot goes far back to the ancient Egyptians where the Sun god, Ra, would rise steadfastly in the east and cross the great river (the Milky Way) of the sky each day and disappear at the end bringing darkness once again to the world.
Cool story, huh? I hope you enjoyed that, because the rest of the constellation is large and empty. Just kidding of course, as Eridanus is filled with wonderful double and multiple stars, and at least two dozen galaxies that are in reach of many amateur telescopes (most 8" and larger). There is not ONE galactic cluster in Eridanus that is viewable in instruments smaller than 24 inches. Only one planetary nebula (ngc1535 discussed below) is within reach in this huge constellation, and there are but two very faint and diffuse nebulae, both of which are so large and spread out that they are but invisible except in wide field extended photographs.
Yet this constellation is by far the LONGEST south-to-north in all the sky. Just look at the chart below: you note that Eridanus' northern boundary rest exactly on the celestial equator...."0" degrees declination. You can trace the boundary of this celestial meandering river all the way past the 9th brightest star of the sky (ACHERNAR) to nearly MINUS 60 degrees south latitude! Sixty degrees of VERY sparsely populated sky connecting observers in New Jersey and South Carolina in the northern skies to those in New South Wales in the southern!
--------------------------------
THE STARS OF ERIDANUS -
For a constellation that extends so far south and with little flare to draw attention to itself, Eridanus has a considerable number of "named" stars, and 10 stars of magnitude 4.0 or brighter! To me, one of the most curious aspects of this constellation from the earliest days in regard to the names of its stars is the fact that all stars in Eridanus were named by the same Arabian stargazers of antiquity that named most all other stars.....names that still stick until today. When you consider that ACAMAR (theta) is at a far south declination of -40 degrees and that ACHERNAR (alpha) is even farther south - minus 58 degrees - it is interesting that such far southern stars were accessible to them in the Middle Eastern world. However, from latitude 35 degrees NORTH, ACHERNAR is just barely below the horizon from my observatory at its highest point.....I have routinely seen this very bright star RIGHT ON the watery horizon of the Gulf of Mexico from Pensacola, Florida on many occasions! On the other hand the star somewhat fainter star Acamar is visible high above the southern horizon from most mid-northern latitude locations.
In the ancient Arab world, with latitudes farther south than most of Europe and the United States, note that the ENTIRE expanse of Eridanus is visible, all the way past its brightest star, Achernar.
NOTE that our most northerly object (in the abbreviated BONUS listing of NGC galaxies found following) is ngc1637, which is located "high" in the constellation at declination MINUS 02 degrees! All objects in this "GO TO" TOUR thus will have negative declinations (south of the celestial equator) and you are cautioned to note that many references to NOT carry through the "-" (minus sign) ahead of the appropriate declination coordinate.
For a complete cross reference of named stars, Bayer and Flamsteed designations, SAO numbers and double stars along with their coordinates, I refer you to the wonderful "Star Tables" at: http://www.gatter.demon.co.uk/data/Eri.htm by British compiler and LX 200 enthusiast Robin Gatter. This particular URL is specifically targeted for Eridanus and every constellation of the sky is so cataloged in this wonderful web site. Take the time to fully explore Robin's fantastic and user-friendly constellation cross-references.
From mid-northern latitudes, the highest stars of Eridanus - those clustered near declination "0 degrees" - rise at about 9 p.m. throughout April; however, not until mid-January do the same stars appear highest in the sky at the same time. Midnight culmination of the same stars always occurs on about December 3 each year, reaching that peak nearly the same time as the very bright white star in Orion RIGEL, just to the constellation's east.
Eridanus is virtually FILLED with splendid double and multiple stars, well over a hundred of which are observable in much detail in telescopes from 3" to 16". Unfortunately I am able to only select a few of the finest double and multiple stars to discuss in our Eridanus "GO TO" Guide; I very much encourage all telescope users to obtain the three-set copy of Burnham's Celestial Handbook for reference on each and every constellation; there is no finer reference work for deep sky viewing to be found.
Also note that a wonderful program is now available for you to install on your computer to CONVERT the epoch 1950-1960 coordinates listed in the Burnham reference tables DIRECTLY to epoch 2000: http://groups.yahoo.com/group/lx90/files/Field%20References%20%26%20Techniques/Coordinates.zip which you can unzip and install within minutes....all you must do is merely type in the coordinates exactly as they appear in Burnhams and enter, with the resulting 2001 conversion done instantly for use with your Autostar or NexStar controller! This wonderful tool was made possible by a program posted on the Yahoo LX 90 site originally and offered as freeware by Meade LX 90 user Ron Gardner.
Once scanning the pages of Volume 2 of Burnhams, you will quickly see the "best multiple" and unusual stars for observations. There are no less than 100 fine multiple stars within reach of most amateur telescopes, many of which are fascinating objects. A few have been selected here as described following.
----------------------------
OBSERVING THIS CONSTELLATION WITH BINOCULARS -
For those who wish to explore the regions of Eridanus in binoculars I highly recommend a standard good quality 7 x 50 or 10 x 50 glass used in very dark, moonless skies away from artificial lighting. Remember to let your eyes become "dark adapted" for at least 15 minutes prior to searching out fainter objects. For a wonderful selection of binocular tour objects, visit http://www.dibonsmith.com/eri.htm, a tremendous guide by Richard Smith from his web page entitled "The Constellations."
--------------------------------
GETTING STARTED -
As with every "GO TO" TOUR guide, each GO TO object in ERIDANUS 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 this HUGE constellation. The chart provided above from the Arkansas Sky Observatory and the subsequent detailed listing of "BEST" objects contains the finest or most interesting from my own observing experience and preference.
Use the attached star chart shown above 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. To access and print the chart, double click on it and save the image to a file on your computer. Once saved, open the file and RESIZE this image to fit the normal paper format for your program and save again....then merely print out the chart on high quality paper for a field reference in this GO TO TOUR!
----------------------------
OBSERVING TIPS -
Every deep sky object and every double/multiple star will have a "PERFECT MAGNIFICATION".....this is the magnification that you should use that will show the object as bright and with as much as detail with possible and still increase its size appreciably so that you can view it comfortably and unmistakably. 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 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.
For detail descriptive lists of the great double stars within ERIDANUS, and 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. For the many double and multiple stars, I again urge you to refer to the indispensable "Burnham's Celestial Handbook", Volume 2 for a complete abbreviated listing.
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.
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 ERIDANUS CONCISE DIRECTORY OF INTERESTING OBJECTS -
As mentioned, Eridanus offers a wealth of fine double and multiple stars (for a full discussion on double star observing and their "Position Angles" refer to my brief overview in the "GO TO" TOUR guide for Lacerta: http://www.weasner.com/etx/ref_guides/lacerta.html ).
The most interesting 10 targets in the constellation have been chosen for this ERIDANUS "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 Meade ETX 60 and 70) is desired over light gathering and magnification of larger telescopes.
Note that your AutoStar may 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 ERIDANUS; you may wish to find many of the objects from the AutoStar Library (for example, you can easily go to the planetary nebula ngc1535, if you pull up "Object/Deep Sky/NGC Object/..then type in '1535'...." and then press "Enter", followed by "GO TO" to access this nice but small and bluish shell of gas.
You will access your FIRST GOTO target - (usually the brightest star in each constellation) - via the command "SETUP / OBJECT / STAR / NAMED....and scroll to EITHER "ACHERNAR" or "CURSA," then press "Enter" and subsequently "GO TO" to move to one of these bright stars. Having TWO stars as our first GO TO object is unique for Eridanus, because of its huge span north-to-south. Since ACHERNAR is so far south as to render it invisible from mid-northern latitudes, the "Beta" star CURSA has been provided for observers "up north;" for those "down under", Achernar will be a much more inviting first target!
You may also access the constellation by: SETUP/OBJECT/CONSTELLATION/"Eridanus".....Enter....GO TO, which will slew your telescope very near the cartographic center of this sprawling star group.
** IMPORTANT NOTE FOR AUTOSTAR, LX 200 AND NEXSTAR USERS **
Beginning with this constellation installment, all COORDINATES for celestial objects will be Epoch 2001, converted from standard and pre-existing star/object data from the most recently (epoch 1950, the standard on which most current star reference guides were based). This change will make your GO TO's far more accurate in the future, as the Earth's PRECESSION in space has caused significant shifting of the apparent placement of objects within the past 50 years!
OBJECT 1:
bright stars -
ACHERNAR (alpha Eri) - R.A. 01h 38' / DEC - 57 15 - Mag: 0.53 - Very far south, 9th brightest star!
CURSA (beta Eri) - R.A. 05h 07' / DEC - 05 05 - Mag: 2.8 - A bit more comfortable position for northern hemisphere! **PLUS double 66 Eridani!**
OBJECT 2:
double star - ACAMAR (theta Eri) - R.A. 02h 58' / DEC - 40 18 - Mags. = 3.5 & 4.5 - very bright and wide white pair, excellent for all scopes!
OBJECT 3:
nice double - 32 Edi - R.A. 03h 52' / DEC - 02 57 - Mags. = 5.1 & 6 - very nice star, good color contrast. Great for all sizes.
OBJECT 4:
quadruple star - B744 - R.A. 04h 22' / DEC - 25 44 - Mags.= 7.3, 7.5, .5, & 12 - Neat star for larger scopes!
OBJECT 5:
test double for 3" - B184 - R.A. 04h 28' / DEC - 21 30 - Mags. = 6 & 7 - very close, 1.6" arc. Good ETX 90 test star.
OBJECT 6:
test double for 5" - 9 Eridani - R.A. 03h 03' / DEC - 07 41 - Mags. = 5.5 & 10 - Excellent test for 5", with 1.9" separation and very faint companion.
OBJECT 7:
variable star - Z Eri - R.A. 02h 48' / DEC - 12 28 - Mag. range 6.5 to 7.9 - Very nice variable for small scopes/binoculars!
OBJECT 8:
spiral galaxy - ngc1232 - R.A. 03h 10' / DEC - 20 35 - Mag. 10.4 - very nice with much detail in larger telescopes! Face-on galaxy.
OBJECT 9:
spiral galaxy - ngc1187 - R.A. 03h 03' / DEC - 22 52 - Mag. 11.2 - large, fairly faint, but two spiral arms visible in larger scopes.
OBJECT 10:
planetary nebula - ngc1535 - R.A. 04h 14' / DEC - 12 44 - Mag. 9, nice small bluish object with 11th mag. central star.
-----------------------------
*** BONUS *** OBSERVABLE GALAXIES IN ERIDANUS - Faint galaxies that are within reach of many common amateur telescopes:
NGC R.A. DEC.(minus) MAG. SIZE (min. arc) TYPE DESCRIPTION
1084 02 46 (-) 07 34 11.0 2.1 x 1.1 Sc Fairly bright, possible in 5", elongated and small
1187 03 03 22 52 11.2 5.7 x 3.7 SB Barred spiral, very large but dim, oval shaped; easy in 8" difficult in smaller scopes
1232 03 10 20 30 10.4 7.0 x 5.5 Sc Very large and fairly bright, round. Can be seen in 3" scopes, but very vague
1291 03 17 41 06 10.1 5.0 x 2.0 El Very nice elliptical, larger than most in area; oval shaped and visible in 3"
1300 03 20 19 24 11.1 5.7 x 3.5 SB Large barred spiral, should be seen in 5"; cigar-shaped smudge
1313 03 18 66 29 10.7 4.5 x 3.0 Pec Very nice in 5" and larger, nearly round and larger than most
1309 03 22 15 24 11.4 1.9 x 1.7 Sc Elongated spiral, fairly small and indistinct; requires 8" or larger for sure
1325 03 25 21 32 12.2 4.2 x 1.1 Sb Nice but very faint, 8" and larger required; very thin wisp of light
1332 03 26 21 21 10.4 3.4 x 1.0 El Nice brighter elliptical, very elongated and brighter toward center; starlike in 3"
1353 03 23 20 50 12.1 2.5 x 0.9 Sb Very thin and faint spiral, nearly edge-on; will require larger telescopes
1357 03 33 13 40 12.3 1.4 x 0.9 S Tiny spiral, looks like a very small oval "ghost" in 8"; 12" will show clearly
IC1953 03 34 21 29 12.3 2.1 x 1.9 Sc Very faint and small spiral with no detail; glimpsed in 8"
1359 03 34 19 31 12.4 1.6 x 1.3 SB An even dimmer barred spiral that is very small and difficult in all scopes
1386 03 37 36 00 12.2 2.5 x 1.0 S Narrow streak of very faint light, just a smudge in larger scopes
1395 03 39 23 01 11.1 2.1 x 1.4 El Fairly bright and small elliptical; easy target in 5" but nearly starlike
1400 03 40 18 41 10.7 0.8 x 0.7 El Extremely small elliptical but great target for 3"; starlike in all scopes
1407 03 40 18 34 10.6 1.1 x 1.1 El Very small but brighter elliptical; starlike
1421 03 43 13 31 11.3 3.0 x 0.6 Sb Nice large and narrow galaxy,nearly edge-on; difficult in 5", distinct in 8"
1518 04 07 21 10 11.9 2.4 x 0.9 Sc Very thin and faint spiral, like a transparent pencil in the 8"; visible in 5"
1537 04 14 31 33 11.8 1.2 x 0.6 S Very small and difficult spiral even in 8" scopes
1600 04 32 05 04 12.1 0.8 x 0.6 El Very tiny elliptical, starlike in 8"; may be glimpsed as a test in the 5" scopes
1637 04 41 02 50 12.1 2.6 x 1.9 Sc Medium sized spiral but very faint; 5" will show it,but 8" and larger preferred
1640 04 42 20 26 11.9 2.0 x 1.1 SB Barred spiral that is distinct in 5" and interesting in 8" and larger scopes
1700 04 57 04 31 11.9 0.9 x 0.8 El Tiny elliptical requiring at least the 5" telescope
----------------------------------
YOUR VISUAL GUIDE TO DEEP SKY OBJECTS IN ERIDANUS
Object 1 - Our "Starting" Bright Stars - "ACHERNAR" (alpha Eri - pronounced: "ATCH-er-nar") / CURSA (beta Eri - pronounced: "KER-sa")
** ALSO - double star "66 Eridani **
The brightest star of Eridanus, 0.6 magnitude ACHERNAR reigns as the 9th brightest stars of the skies encircling the Earth....yet most of the worlds population has never seen it. At latitude -58 degrees as stated above it never reaches high enough above the southern horizon to be seen anywhere north of about north latitude 30 degrees. However, for our observers "down under" this is a benchmark star and a beacon of late fall skies. From the Arabic "Bright one at the River's End", this star name is one of my favorites, signifying the long 60-degree run from north to south of our celestial river, Eridanus. We can only imagine ancient mariners skimming the waters of the southern seas using this bright star as their guide. On about October 20th, the star "might" be seen at midnight immediately over the waters of the Gulf of Mexico from Florida, Louisiana and Texas as well as from all of the Hawaiian islands. It is not visible from the Mediterranean countries. Achernar is an extremely "early" type bright white star that is quite larger than our own sun.....glowing brightly at a distance of only 120 light years.
Nowhere near as bright, but still conspicuous for more northerly observers is Beta Eridani, CURSA, shining at a seemingly pale magnitude 2.9. However, this star is VERY close to our solar system (80 light years) and more evolved than is Archernar. Cursa is best found as the brightest star northwest of the distinct RIGEL in the "feet" of Orion. NOTE: look for the fine wide double star 66 Eridani just to the WEST of Cursa, easily spotted in the same very wide field of view with your telescope; 66 ERI is a true double with a 6th magnitude primary star and a 9th magnitude companion about 1 arc minute due north, a wonderful and easy target for most telescopes.
Object 2 - The Fine Double Star ACAMAR (pronounced "ACK-mar") - (theta Eridani)
Although this star is VERY low in the southern skies, it still can be seen by observers in the southern United States and other locations south of north latitude 35 degrees. This is an interesting star, both from its brilliant white appearance of its magnitude 3.4 and 4.4 stars, but also because both stars are moving uniformly through space without any signs of orbital motion around one-another! Separated at about 8.3" arc, this pair has been so observed since John Herschel began accurately measuring their Position Angle and separation early in the 19th century from South Africa. The Greek Ptolemy cataloged this star and ranked it among the brightest, or his "of the first magnitude." Today, the star is almost 3rd magnitude so we are witnessing a star that likely has actually FADED in luminosity in recorded history. Nearly the same spectral type star as Achernar (see above) and at nearly the same distance (only five light years closer than the bright Achernar), it is likely that both these stars are fairly new stars.....with Achernar a blue-giant and Acamar and white, slightly more evolved star. Hence its slight age difference might account for its dimming from simple nuclear stabilization, whereas Achemar (a "B" type star) is still very much in its formative stages, much like the bright blue stars of the Pleiades star cluster.
Object 3 - A Colorful Double Star - 32 Eridani - Nice Object for All Scopes
This is a BEAUTIFUL double star, with a wide separation of 6.9" and thus resolvable in all scopes larger than 3". The primary is an orange-yellow 5th magnitude star, while its companion is a 6th magnitude star of brilliant white color. So very near the celestial equator at only minus 03 degrees, this is a must-see for telescope users. At present the stars are oriented in a nearly north-south direction
Object 4 - A Challenging Quadruple Star! "Burnham 744"
(see my discussion on double star positions and observing at: http://www.weasner.com/etx/ref_guides/lacerta.html )
This is the 744th multiple star measured carefully and cataloged by the famed S.W. Burnham, the father of American double star observers. His keen eye and carefully measured stars have served as the benchmark for our observations today, noting the orbits, periods and even the masses of thousands of double and multiple stars. B744 is an unusual Quad Star, the primary component being a PAIR of equal brightness magnitude 7.4 stars. At present, these stars are as far apart as they have been since their discovery in the 19th century. Although the Position Angle (see chart below) is not appreciably changing since its discovery, the distance between these two very close stars is increasing. Right now the stars measure some 0.9" arc apart, theoretically far enough apart for resolution with a 5" telescope; however, I have had considerable difficulty resolving this star, partly because of its very southerly position (-26 degrees declination) and thus unsteady air currents between my telescope and the star. An 8" telescope resolves it cleanly into a neat yellow pair.
Observers south of 35 degrees north latitude are encourage to attempt to resolve this star, and report what telescope, seeing conditions, magnification required if successful. HOWEVER...don't stop there! There are two more parts to this star! The chart above shows the 12th magnitude "C" companion a wide 39" arc due north of the difficult "A" and "B" pair; this will require at least a 5" telescope simply because of the faint magnitude. NOW....look almost the same distance (but a little farther) as that faint star is from the A-B pair almost northeast (Position Angle 41 degrees) to find the "D" component, a much brighter star 8.5 magnitude, a good target for a 3" scope. Actually, if you will find the "D" star first and then look for the "C" star, you will have a better idea of how far that one is from the brightest pair. Thus, in one star, we have a Quad star that works as follows: TWO stars (the A-B combo as one star and "D") can be seen with a 3" scope; THREE stars (A-B combo as one star, "D" and "C") and all FOUR stars with an 8" or larger scope. Keep in mind that the keen-eyed observer with a 5" scope, good steady skies and high magnification CAN split the "A" and "B" components!
Object 5 - An Easier Test Double for the 3" and 5" Scopes - Burnham 184 (B184)
Can your 3" scope hit Dawes' limit? Here is a nice test to find out. B184 is a pair of magnitude 6 and 7 stars, with the fainter star 1.5" arc away from the main star in Position Angle 252 (nearly due west). A 3" scope should be able to resolve two stars of equal magnitude under steady conditions that are 1.3" arc apart. Hence, this one should be tough, but do-able. If the air is steady, use as high magnification as you need; you will first see the point of light "elongate" in an E-W direction with high power and finally separate with some nice dark sky between them with even higher power. NEVER hesitate to use high magnification on nights of very good steadiness. For a complete discussion regarding how "seeing" and air transparency affects your viewing, go to my discussion at: http://www.weasner.com/etx/buyer-newuser-tips/seeing.html . I routinely use over 50x per inch aperture to observer planets and doubles stars when the conditions are favorable; the old myth that higher powers are useless on telescopes are not true with today's Null-figured optics and excellently corrected eyepieces.....it is the AIR around us that limits the "power potential" of your telescope.
Object 6 - Now...a Test Double for a 5" Telescope! - "9 Eridani" (also Rho Eri)
There are actually THREE stars that comprise the designation "Rho Eridani", with the Flamsteed numbered star "9" being the middle of the three; actually they comprise a very pretty small triangle in the very northwestern part of the constellation, and hence are very accessible for northern viewers. Our double star is the southern "apex" of this triangle. This star is steadily closing and at present there is about 1.7" arc separating "A" from "B" (see chart below). The brighter star (A) is magnitude 5.5 and hence very easy to spot as the middle of the three "Rho stars." However, it is the faintness of the "B" star (magnitude 10.4) that requires the aperture of the 5" or larger telescope, not the distance between them. The fainter star will be quite difficult to make out from the very bright orange glare of the primary star. Look for "B" slightly north of due east from "A."
Object 7 - A Fun and Easy Semi-Regular Variable Star (accessible from northern latitudes, too!) - Z Eridani
This variable star is one of many interesting and yet-to-be-understood "Semi-Regular" stars; such stars demonstrate a "suspected or slight" regular period between brightening, dimming and then re-brightening again (about 80 days for this star), but are characterized during that period by sometimes major fluctuations....unexpected dimming or brightening....long periods at maximum or minimum....very rapid brightness increases followed perhaps by extremely slow fading....and so on. Hence the need for YOUR observations of such stars. Even with a period of only 80 days, this star should be observed at least once weekly when possible. For a complete discussion on this classification of variable and methods for observing variable stars, see my guide at: http://www.weasner.com/etx/ref_guides/variable_stars.html .
Z Eridani is one of the brightest of all semi-regular stars, fluctuating in brightness from magnitude 6.4 to 7.9. It is a VERY red, red giant star, of the extremely late "M" class spectrally. Its wild fluctuations are well known and the star is well worth the watching. Because of its brightness throughout its cycle, it is visible in small telescopes and even binoculars with the proper chart. A chart is necessary to: 1) find the right star to watch; and, 2) have stars provided nearby with magnitudes given that have been correctly checked as accurate through which brightness assessments can be made. For such brighter stars needing likewise bright comparison stars, one must choose a wide angle chart that features a large chunk of sky. The American Association of Variable Star Observers (AAVSO) provides complete charts for virtually every variable observable with common telescopes. The wide-sky "finder" charts are designated "a" charts. The proper chart for Z Eri for both locating and observing its magnitude changes is: charts.aavso.org/standard/CET/U_CET/UCET-A.GIF actually a chart specifically for "U Ceti" (Cetus) but also including the location and comparison charts for this star as well.
Object 8 - Finally - a "REAL" Deep Sky Object in Eridanus! - A Face-on Spiral Galaxy - NGC 1232
The striking photograph above of this classic galaxy was taken with the still-magnificent Palomar 200" telescope in California. This is a fabulous face-on spiral galaxy located near the middle (north-to-south) of Eridanus at about -20 degrees from the celestial equator. This low angle for northern observers in not too much of a hindrance until attempting to observe this magnitude 10.4 object. It is a fairly large galaxy to view (7.7 x 5.5 minutes arc) so its brightness is spread out over that area. It is visible as a small round "glow" in a 3" scope under VERY dark skies with no moon; much clearer in a 5" and 6" scope and affords some interesting detail with the 8" and larger scopes. I have clearly seen three of the brightest "knots" of stars in the spiral arms and suspected a fourth visually with a 12" Schmidt. The many arms of this spiral are very clear, but extremely faint, visually with the 24" telescope at 212x.
Object 9 - Another Spiral Galaxy - NGC 1187
Almost a duplicate of the many-armed spiral ngc1232 (above), this spiral is considerably fainter. At magnitude 11.2, it is still visible in smaller telescopes, though void of any discernable detail in telescopes smaller than 12" diameter. In large scopes, the spiral arms very much resemble those seen (and photographed) with ngc1232. It is slightly smaller than the former and without the "clumping" in any arms; thus even larger telescopes visually show nothing but a circular disk of very faint light.
Object 10 - A Nice Planetary Nebula - NGC 1535
This is the ONLY planetary nebula visible visually in any telescope in the constellation of Eridanus! NGC 1535 is a fairly small (20" oval shaped) cloud of blue-appearing gas. It stands out unmistakable amidst the black sky and very star-poor background of north-central Eridanus. Look for this small disk of light nearly due east of gamma Eri (ZAURAK) by nearly 5 degrees and since the object is high in the constellation, it is a good target for all telescopes in the northern hemisphere. The distinctive blue color is just beautiful and at first glance it stands out much like a small blue planet or other body, almost 3-dimensional. After you find ngc1535, increase the magnification to about 30x per inch to magnify the scale of this interesting sight. Right in the middle is a central star of magnitude 11.5 which can be glimpsed fleetingly with a 5" or 6" scope. It should hold steady with an 8" instrument. It is this star that "exploded" in the prehistoric past creating the planetary nebula that we now see. The nebula is a relatively bright 9.3 magnitude, so this nice object should be observed by all.
----------------------------------
WANDERING ABOUT....YOUR NEW "USER OBJECT" IN ERIDANUS
Here is a beautiful object whether you are viewing from either the northern or southern hemisphere. OMICRON 2 ERIDANI (also known as Flamsteed's "40 Eridani") is comprised of two brighter stars, both about 4th magnitude. It is located very near "Omicron 1" (the northernmost star with a fairly bright star (37 Eridani) immediately to its west; both of these are clearly visible together in your finderscope or in binoculars); immediately below (south) is "Omicron 2", is our fantastic triple star. Although easily seen as double in even small telescopes, the duplicity of this star was not "discovered" until Sir William Herschel cataloged it late in 1783. A 2.4" refractor held steadily will reveal the "A" and "B" components of this wonderful star, separated by a whopping 83" arc, about two Jupiter diameters as seen in the same eyepiece. The only difficulty in observing with the smaller telescope is in the faintness of the "B' component, at magnitude 9.3, compared to the bright primary "A" star, at magnitude 4.4 ("Omicron 2"). See the chart below for locating the fainter star.
This is an exciting object, not just from the wonderful view afforded by the two "A" and "B" components, but the fact that the "B" star....fainter star....has yet ANOTHER star encircling it as well! We note in the chart above that "B" is in Position Angle 105 degrees, or nearly due west and a slight bit south of the bright star. It is this fainter star that is also double. Circling "B" is an 11th magnitude "C" star in Position Angle 347 degrees from "B" (we do not measure its angle from the primary, but from the star which it orbits which, in this case, is "B"). So look for the third star just about straight north (a bit to the west) from the 9th magnitude "B" star.
Of course you can use the chart above to find the star quite simply with your finderscope, but it will always be ready for you to GO TO if we add it among the growing library of "User Objects" on your computerized Autostar. Coordinates (corrected for epoch 2001) for OMICRON 2 ERIDANI ARE:
R.A. 04h 14m
DEC -07 37
On AutoStar, go to: "Select/Object [enter]...." scroll down to "User Object" [ enter]. Now enter the coordinates given above for OMICRON 2 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 "4" [Enter].
----------------------------------------
Next Constellation GO TO" TOUR Installment: LEPUS....."ehhhh, what's UP doc?" What's UP in the Southern hemisphere is DOWN for Northern observers.....Lepus, the celestial hare.....the "widdle, wascally wabbit of the winter wonder-world." The celestial bunny might have been better suited for the spring skies of Eastertime, but perhaps if he had delayed for the warmer spring weather he would be even further on the heels of the tortoise (which there is no such thing in the 88 constellations, but it makes for good conversation when you show your skywatching visitors to the winter star party the Leaping Rabbit below the feet of Orion! And...have fun with the carrot by encouraging them to find it in this small constellation....it's not there.
Good Observing and may the stars serve as your sentries as you explore the frontiers of space!
P. Clay Sherrod
Arkansas Sky Observatory
Conway / Petit Jean Mountain
Arkansas
Return to the top of this page.
Go back to the Observational Guides & References page.
Go back to my ETX Home Page.