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Posts Made By: Herbert Kraus

August 17, 2006 10:03 AM Forum: Deep Sky Observing

"The Sickle" in Cygnus

Posted By Herbert Kraus

I came across an attractive group of stars or asterism earlier this week, and although others have surely noted it I haven't seen it referred to in my observing books and will mention it here: I was looking at open cluster IC 4996 in Cygnus and found a small semicircle of stars -- a miniature Corona Borealis -- just south of it. With a couple of fainter stars forming a "handle," the group is shaped just like a sickle, and I so named it. The tip of the sickle is 5th magnitude 29 Cygni, and the other stars making up the blade and handle vary in magnitude from 6.5 to 9.1. Its coordinates are approximately RA 20:13 Decl + 37.1º.

September 29, 2006 10:00 AM Forum: Deep Sky Observing

Observation Report: Open Clusters

Posted By Herbert Kraus

This will be a fairly lengthy report, of interest mainly to those who also like to view open clusters.
On September 26, 2006, I took my 8-inch SCT to the Cottonwood Springs Campground area of Joshua Tree National Park, California (elevation about 3,700 feet), to observe galactic clusters. It was a warm night -- short shirtsleeves weather -- under totally still skies. The seeing was generally very good and the sky appeared very transparent at the beginning of my observing session, though less so later in the night. The quality of viewing was only slightly affected during the early hours by the waxing crescent of the 4-day old moon, and the summer milky way from Cassiopeia through Sagittarius and Scorpius was plainly in view.
I started the session in Scorpius, first visiting my brilliant old friends NGC6231, M7 and M6. Although the constellation was already too low in the southwestern sky for several of my targets (NGC6249, 6259 and 6322), I did view five open clusters in Scorpius that were new to me (described below). I studied each of these targets with a 20 mm eyepiece, my favorite for open clusters, at 102x.
NGC6242 is a fine little cluster in which I counted 13 individual stars scattered among a hazy swarm of unresolved members. The texts I use (Archinal & Hynes and Luginbuhl & Skiff) rate this as a cluster of 23 stars within a diameter of 9 arcminutes with a total visual magnitude of 6.4
NGC6400 also offered me a swarm of mostly unresolved stars, peppered with a few dim individually discernible stars. Its appearance reminded me of some of the more extensive globular clusters, like M4 and M55, that do not have an obvious bright core; the similarity of NGC6400 to such globular clusters was enhanced by what appeared to be several "strings" of cluster stars radiating out from its circumference. This cluster is rated as containing 60 stars within a diameter of 12 arcminutes. I concluded that most of the cluster's stars were among those unresolved in my view of it, and this is consistent with its total visual magnitude rating of 8.8.
NGC 6416 is a fairly bright open cluster, with a total visual magnitude rated at 5.7, but I found it difficult to differentiate the swarm of stars comprising this cluster from the star fields of the milky way that surround it. My difficulty is apparently confirmed by the experts: Luginbuhl & Skiff states that "this cluster is hardly distinguishable from the field" (in a small aperture) and says its diameter is 30 arcminutes; while Archinal & Hynes says its diameter is 15 arcminutes; but both agree that NGC6416 contains 304 stars.
The other two Scorpius clusters I viewed this night, NGC6425 and NGC6451, are also situated among the star fields of the milky way, but both appeared to me to be in front of dark areas within those star fields (dark nebulae?), making them more obvious and identifiable.
As to NGC6451 I thus disagreed with Luginbuhl & Skiff which claims that this cluster does not stand out well from the rich background; I saw it as a fine swarm of unresolved stars, with a few dim individual stars sprinkled among them, of which I counted 16. The texts rate NGC 6451 as a cluster of 80 stars within a diameter of 8 arcminutes with a total visual magnitude of 8.2. It is one of the objects on the Herschel 400 observing list; I have seen it referred to as the "Tom Thumb Cluster."
NGC6425 is a triangular-shaped group of stars that appeared to me like a much smaller and fainter version of M39. Since that brilliant cluster in Cygnus is too extensive to fit within the field of view of any but the lowest power wide-angle eyepieces I have, I now know where to look if I want to see M39's equivalent without the hassle of changing eyepieces! The texts rate NGC6425 as 73 stars within a diameter of 10 or 15 arcminutes and with a total visual magnitude of 7.2.
One other open cluster that I viewed this night that was also new to me was NGC1342 in Perseus. This is a cluster of relatively bright stars, of which I counted about 25, in a box-shaped pattern within a fairly large area. The texts rate it as 99 stars (most of them obviously unresolved by me) within 17 arcminutes and with a total visual magnitude of 6.7.
I did not log my impressions of the many other objects I viewed this night that were already familiar to me, but they all appeared at their best as I peered at them. They included all of the Messier objects in Sagittarius, Capricornus an Scutum, as well as NGC457 and 7789 in Cassiopeia. I also viewed Uranus and Neptune (with a 6 mm orthoscopic eyepiece at 339x), and either saw or thought I saw Neptune's moon Triton about 8 Neptune diameters to the east of the planet.

April 26, 2007 10:54 AM Forum: Solar System Observing

Memorizing the Maria: Another Suggestion

Posted By Herbert Kraus

An amusing recently posted thread viewed the lunar maria as Jack, of Jack & Jill, and a beaver, but some of us had difficulty figuring out how to memorize the names of the maria on this basis.
Suppose you do it this way: Starting with Mare Crisium, which is the first to appear in the lunar cycle and sits by itself near the moon's eastern edge, move around clockwise in an inward bending spiral path in this order: Crisium, Fecunditatis, Nectaris, Nubium, Humorum, Procellarum, Imbrium, Frigoris, Serenitatis, Tranquillitatis and ultimately Vaporum. The first letters of the names of the maria in this order might be memorized by this mnemonic: CINDERELLA FOUND NO NEW HANDSOME PRINCE IN FAIRYTALE STORY TOLD VICIOUSLY. I'll attach an image to illustrate it.

May 24, 2007 10:18 PM Forum: Deep Sky Observing

"Oh the Globs That Glow in the Spring, Tra-La"

Posted By Herbert Kraus

Warning: This observing report will be rather lengthy and of no interest to anyone except fans of globular clusters. It's my report of an observing session last Tuesday, May 22, at Cottonwood Springs, Joshua Tree National Park, California, one of my occasional dark sky observing sites. At such occasions I usually seek out open clusters, but my sky atlas told me that there are few or no such objects between the milky way's northern winter arm (Auriga, Taurus, Gemini, Orion, Monoceros, etc.) and its summer arm, and I had no intention of spending the wee hours of the morning at this location. Moreover, the multitude of galaxies in our evening skies in Spring would be beyond the grasp of my equipment on this evening when the sky was washed in the light of the 5-day old moon -- except for bright M51, M81 and M82, which I dutifully viewed before the evening was over. So my observing agenda consisted of a list of globular clusters that lie in our northern hemisphere skies east of the winter's milky way and west of "globularland" in Ophiuchus, Scorpius and Sagittarius.
My usual practice is to list the objects I plan to view, note down my impressions of them, and afterwards compare what I saw with the comments in the observing handbooks in my library. I viewed these globulars at 102x through a 20 mm eyepiece in an 8-inch SCT.
***M68 in Hydra struck me as a rather shapeless globular cluster, in the southerly reaches of which I detected a few individual stars and which seemed somewhat remarkable to me for not displaying a core region that was distinctly brighter than its outer reaches. My impression was consistent with the descriptions of M68 as seen in lower aperture instruments as a "weakly concentrated circular glow" (Luginbuhl & Skiff) and as a "faint, large oval haze" (Webb Society handbook, vol. 3).
***NGC 5694 in Hydra appeared to me as a nondescipt fuzzball of approximately the same magnitude as two stars that lie just southwest of it in the same field of view. Luginbuhl & Skiff said of this cluster seen through a 25-cm (10-inch) instrument that "The cluster is 2' diameter and shows no resolution," and that is how I also saw it. Later I found out that NGC 5694 is one of the Herschel 400 objects; and that it is #66 in Patrick Moore's Caldwell list, and a photo of it on page 263 of O'Meara's book about Caldwell objects tends to confirm my visual impression.
***M3 in Canes Venatici is my nostalgic favorite, because it was the first bright globular cluster I had ever seen. On this occasion it was a brilliant sight, even in this moonlit sky, showing a bright core that appeared almost three-dimensional and revealed extensive granularity, surrounded by a halo of unresolved members.
***NGC 4147 in Coma Berenices (also a Herschel 400 object) is a small, tight fuzzball that seemed somewhat oval in shape to me, with its east-west dimension somewhat exceeding its north-south dimension. My impression was consistent with the Webb Society observer's description of NGC 4147 as a "Very faint, small oval; elusive object." But I did not see it as having a bright core or nucleus as did other Webb Society observers and Luginbuhl & Skiff.
***M53 in Coma Berenices showed me a bright core with a halo of unresolved stars extending mainly in the north-south directions, and I did not observe any evidence of individual stars or granularity, nor of any strings of stars leading away from the cluster. Luginbuhl & Skiff seems to confirm my impression of the non-circular halo in stating that most of the "outliers" are on the NW and SE.
***NGC 5053 in Coma Berenices and NGC 5466 (a Hershel 400 object) in Boötes: to my disappointment, I could not find these globulars this night, although I had previously viewed NGC 5053.
***NGC 5634 in Virgo was a bit of a challenge. I saw an east-west string of three stars, and just northwest of the easternmost of them a small rather shapeless glow that I would have taken for an out-of-focus star but for the fact that the other stars in the field of view were in good focus. This was evidently NGC 5634 which Luginbuhl & Skiff says "is set among three mag. 8.5 - 11 stars, the brightest located only 1'.3 ESE of the center." The cluster is referred to as compact and unresolved in my observing handbooks.
***M5 in Serpens Cauda was a brilliant apparition, bigger and brighter than M3, with a granulated three-dimensional appearing core, several strings of outlying stars, and an extensive halo that made the cluster appear to be stretching away from the globular or spherical shape. This last feature is noted in Luginbuhl & Skiff, which says: "More outliers spread to the S, W, and N than to the E, giving the halo an asymmetric form."
***M13 in Hercules was, by visual dimension, easily the largest of the globulars I viewed this night, but interestingly it consisted mainly of its brilliant granulated core, without the extensive halo exhibited by M5 and M3. I saw many individual stars and strings of stars in and around M13.
***NGC 6229 in Hercules appeared to me as a small round fuzzball, which, however, showed me a distinct halo surrounding a brighter core. This feature was not mentioned by Luginbuhl & Skiff, but the Webb Society observer with a 16½-inch instrument noted that the central area appeared "almost stellar x70."
***M92 in Hercules was a good, bright globular cluster, wtih an extensive halo around a bright core, which I likened to a dimmer version of M5.
By the time I had completed my observations of these objects, the top of Scorpius (with Jupiter) had risen in the southeast, and all of Ophiuchus was now above the eastern horizon. To complete my observations of globulars, I took in M12, M10 and M14 in Ophiuchus, all of which were impressive as they usually are in dark skies (even though the bright moon was still well above the western horizon). I then peeked at M4 in Scorpius, and noted that this was surely the most chaotic of the globulars, appearing as a rather shapeless halo of stars, a large but relatively dim expanse of nebulous fuzz, although its appearance on this occasion may have been adversely affected by the fact that it was still fairly low on the horizon when I looked at it and was preparing to depart.

June 17, 2007 08:37 PM Forum: Deep Sky Observing

Classification of Globular Clusters

Posted By Herbert Kraus

Last month I posted an observing report about the globular clusters of Spring. This weekend I observed the globs of Summer at the monthly "dark sky night" at our L.A. Astronomical Society's Lockwood Valley observing site. Initially, my agenda was to observe all of the globs of Ophiuchus (which is to globs what Virgo is to galaxies and what, for us northern hemisphere observers, Auriga is to galactic clusters). I listed 27 of these objects (including M62 on the border with Scorpius and NGC6539 on the border with Serpens), of which 7 are on the Messier list and no less than 13 are among the Herschel 400 (including NGC6171 which is also included among those on the Messier list as object 107). I had intended to view them in the order in which I had listed them, by declining magnitude, from bright M12 (magnitude 6.1) down to Palomar 15 (magnitude 14.2) and PWM78 2 (unknown magnitude); but as the night wore on and I was trying to see detail in 9th magnitude objects I ended this quest after observing 13 of the Ophiuchus objects and instead looked at numerous globs in other constellations.
When I later tried to produce coherent observing logs from the notes I had hastily scribbled in the field, I discovered that my visual impressions of these objects placed them into a few distinct categories. In addition to their variations in visual magnitude and diameter, which may be attributable to their distance as well as their intrinsic size, some of these globulars had distinct bright cores, others not; some had extensive halos of unresolved members, others not; for some the transition or borderline between core and halo was sharp, for others it was gradual; some were surrounded by outlying resolved stars, others not; some appeared to be round or spherical (i.e., globular), and others appeared oval or shapeless. I looked for some established system of classification, like the Trumpler classification system that is used for galactic clusters.
I found two kinds of classification systems for globulars. The kind used by serious scientists and astrophysicists is based on spectroscopic and statistical analysis and, though interesting, is of little use to amateur visual observers like me. The other system contains 12 classes based solely on the "concentration" of these objects, ranging from Class I (the most highly concentrated) to Class XII (the least so). This system is mentioned and applied to objects listed in Burnham's Celestial Handbook and in the Webb Society's Deep-Sky Observer's Handbooks (where it is attributed in one case to Harlow Shapley and in another to a 1965 publication by Halton Arp), but nothing in my library explains it further.
Can anyone guide me to a system by which globular clusters are classified on the basis of their several principal visual attributes, as these appear in our telescopes, or do I have to make up my own system?

August 13, 2007 11:11 PM Forum: Deep Sky Observing

Which Galaxies Should We Observe?

Posted By Herbert Kraus

I am seeking advice from experienced observers of galaxies for my club's scheduled viewing session next Friday at the venerable 60-inch telescope on Mt. Wilson. Since my usual viewing site and viewing equipment -- both optical and anatomical -- are unsuitable for most faint fuzzies, I use this occasion to expand my observing horizons. Last year I made it a point to view planetary nebulae at the 60-inch. This year, I plan to ask the man at the console to show us some particularly interesting galaxies, and would appreciate any suggestions here on Astromart, subject to the following constraints:
1. I can't use a long, long, list, being only one of 20 or so observers who will bring their own preferences. Which are your 6 prime candidates?
2. It's an all night session (weather permitting), so we will probably be able to look at objects from about 14 hours right ascension (Friday evening) eastward to about 6 hours right ascension (Saturday morning).
3. At 34º north latitude our southern horizon is about 56º south declination, but the instrument is not equipped to look that far south. The practical southerly limit of the objects to view may be about 10º south declination.
4. Remember that this is a very large instrument that tends to produce a very small field of view. That's why I am not seeking to look at any nebulae, and any galaxy that approaches the visual dimensions of M31 or M33 would be inappropriate in my opinion.
Any suggestions will be much appreciated.

August 21, 2007 06:03 PM Forum: After Dark

Recommended Reading for Those Who Love Dark Skies

Posted By Herbert Kraus

The August 20, 2007, issue of "The New Yorker" magazine has a fine article entitled "The Dark Side" beginning on page 28. It celebrates the beauties of dark night skies such as our ancestors were used to, and explains the adverse effects modern life and fixtures have had on the darkness of night, and what is being done about the problems by the International Dark-Sky Association and others. It's the first time I've seen this subject so sympathetically treated in the mainstream press, not just in journals for amateur and other astronomers, and those of us who care about these matters would do well to share this article with our families, friends and acquaintances.

October 29, 2007 11:51 PM Forum: Comets

Comet 17P/Holmes October 29 - 30

Posted By Herbert Kraus

After viewing Comet 17P/Holmes at around 8:55 pm PDT on October 29 (03:55 UT October 30), I am posting this report because the seeing on this evening was exceptionally good (my tests for seeing quality are to determine whether I can split the Lyra double doubles without a high degree of magnification; and whether the brilliant redness of T Lyrae is evident in my eyepiece). I have seen the comet twice before in the last few days, but never this clearly.
The comet appeared as a roughly circular apparition about 7 arcminutes in diameter, although the westerly edge of the circle was sharper and somewhat rounder than the fuzzier eastern edge. The noticeably brighter inner portion of this "disc" was about 2 to 3 arcminutes in diameter, and contained a star-like core or kernel near its northwestern edge, whose visual magnitude I guessed at about 8. Several stars also appeared in my field of view. I judged the brightest one to be of about 7th magnitude some 15 arcminutes west of the comet's edge. I thought this might be 43 Persei, but subsequent research indicates that that is a 5.5 magnitude star located somewhat to the east of where the comet was at this time; it might have been SAO 024223, a 7.9 magnitude star located 15 arcminutes from the comet's position this evening.

March 27, 2008 04:18 PM Forum: Deep Sky Observing

Discovering NGC 2477

Posted By Herbert Kraus

Earlier this week I did some star-gazing at the Cottonwood Springs area of Joshua Tree National Park, where I spent an evening methodically seeking out galactic clusters in the Monoceros-Puppis region. The sky was reasonably dark and the seeing was generally fair, neither the best nor the worst I have encountered in several years of winter-time observing at that location. I will not burden you with a detailed report, but I will mention one open cluster that I had not seen before and that immediately became one of my favorites. It's NGC 2477 in Puppis, which has probably not made it into the Herschel 400 only because of its southerly location at declination -38º, although Patrick Moore included it as item #71 of his "Caldwell" objects. This brilliant cluster immediately reminded me of two long-time favorites of mine, NGC 7789 in Cassiopeia and M37 in Auriga. These three are all enormous swarms of hundreds of suns which are near and extensive enough to be individually resolved in reasonably dark skies, but the great majority of which appear to lie within a narrow range of rather faint visual magnitudes, avoiding the appearance of a scattered handfull of sparklers in a sea of nebulosity. NGC 2477 filled about half of my 20 mm eyepiece's 30-arcminute field of view. Archinal & Hynes says this cluster includes 1,911 stars within a diameter of 20 arcminutes and with a total visual magnitude of 5.8. The equivalent ratings for NGC 7789 are 583 stars, 25 arcminutes and magnitude 6.7; and for M37 they are 1,842 stars, 15 arcminutes and magnitude 5.6. I recommend NGC 2477 to any observer of galactic clusters for whom it is within reach, and for those of you located too far north for this cluster I suggest that you put it on the agenda for your next trip to the south.

September 11, 2008 12:55 PM Forum: Deep Sky Observing

Please identify this DSO

Posted By Herbert Kraus

I am attaching the image of a postage stamp issued in 1998 by the Pacific island nation of Palau in honor of the Hubble Space Telescope. Can anyone identify the deep sky object or objects shown behind this cutaway view of the HST? Presumably this is an image taken by HST, but I could not find it among the HST images of DSOs in several books of such images.