Saturday, 28 April 2012

Cosmic Challenge by Philip S. Harrington - A review

Cosmic Challenge - The Ultimate Observing List for Amateurs by Philip S. Harrington
Cambridge University Press (November 30, 2010)
ISBN: 9780521899369
466 (true) pages

Rating: 8/10 - Recommended









The ultimate observing list for amateurs. With such a name for a book you're entitled to some serious challenges from the night sky. I have to admit, I wasn't sure about getting this book. The main reason was, that I don't like digital sketches and I knew Philip's are digitally made. For me, such sketches easily spoil any book, article or anything they're associated with. Using, say Adobe Photoshop might let you do all the work with a computer but even a simple diffuse, nebulous glow is something that a computer cannot do properly without making it look otherworldly. And digital sketches hardly represent the true eyepiece view - this is the main reason why I dislike them.

So how are the sketches in the book? Well, surprisingly good. There are some bad apples to my eye in the bunch such as: M57 and NGC 7331 to name a few. The biggest problem by far in the book is that the most of the sketches are so low contrast that you actually have to us averted vision to spot them! I understand this is to represent the difficulty of the objects and how they even can look at the eyepiece but contrast up man! This issue was already discussed in CloudyNights.com but I was surprised at how obvious it was. Also, the accuracy of star placement in some of sketches is staggering to a point I wonder if they've been actually done to a printed starfields? I'm not saying such accuracy is impossible to achieve - it would just literally take hours. Most of the drawings have very, very high accuracy but some have some misplacement here and there but this is rare. So I suppose the original sketches are handmade.

What of the actual challenges? You can, of course, have many thoughts about them. I love the fact that there are so many of them and more importantly for all apertures! What a great idea to have some naked eye challenges for a start! I would have liked to see sketches of them too which sadly are missing.

I personally would have changed several objects to different telescope categories but this isn't MY book is it. I'm glad there are some real challenges (although a bit too obvious ones) for monster telescopes (15 inch aperture and larger) such as Einstein's Cross, Hickson 50, Seyfert's Sextet and so on. From my point of view, some of the monster telescope challenges should be in large telescope challenges instead (10- to 14 inch telescope). Such objects are Leo I, IC 1613, (brightest of) M31 globulars, Terzan 7, WLM, Simeis 147 are most certainly small telescope challenges (although being difficult with larger ones as well). For example the author speaks of how difficult it is to observe the entire Simeis 147 at once in the narrow fields of view of large aperture telescopes. Could there be a better place for a high quality, wide field refractor than this? No! Especially considering that there are many observations of the object seen only with apertures around 4 inches! Some other that did hit the eye were galaxies beyond M44 (if you remember, Steve Waldee has seen all of these listed in the book with his 10 inch telescope!), Copeland's Septet, PK 164+31.1 (both visible with 8 inch aperture) and several other galaxies and groups should at least be downgraded to the "large telescope challenges" for sure. But most of the "bad" things in the book can be discarded as matter of opinion and personal taste. Other little things I noted (desperately grasped on) include:
  • If you see M13 (non stellar, 5.7 magnitude object) with the naked eye - your naked-eye limiting magnitude can't be 5.5 but is more likely 5.9 at least.
  • Seeing M33 with the naked eye doesn't really need "absolutely, perfectly pristine skies". It is actually quite easy to see even from Finland which isn't even remotely absolutely, perfectly pristine anything.
  • Chart 5.19 IC 10 (page 264) says "Sculptor". It probably should read "Cassiopeia".
If you want something simple and short, here it is: the book is simple (in a good way), easy to navigate and the charts are most excellent. It is well written and while some might argue the text portions are a bit on the short side, I don't find this a problem but actually a bit of a relief (after reading O'Meara). Despite my - at first - biased view of it, the book is far from bad. It is quite excellent and I would recommend it to... well every amateur astronomer out there. And good to see my friends and colleges Timo and Steve mentioned in the book as well. I'm looking forward to volume 2.

8/10 for every living soul - Recommended

Friday, 13 April 2012

5 curious and nearly unknown nebulae for photographers

Have you already taken a photo of every Messier object in the sky - twice?
Nothing in MegaStar that you haven't already photographed?
Looking for something different? Here's your chance!

Image courtesy of DSS (Digitized Sky Survey)
LBN 437(a) / V0375 Lac (Markarian 914)

Coordinates: 22 34 05 +40 42 36 (Lacerta)

Eastern part of the LBN 437 complex - designated here as LBN 437a. Small 2.5' nebula concentrated around the variable star V0375 Lac - sometimes credited as a galaxy Markarian 914. The size of the whole eastern complex is roughly 20'.










Image courtesy of DSS (Digitized Sky Survey)
LBN 437(b)

Coordinates: 22 30 13 +40 28 13 (Lacerta)

Western part of the LBN 437 - credited here as LBC 437b. Total size is roughly 30' x 12' and forms a shape of a dragon, monkey or a lizard. You decide. Bright star near the "head" of the dragon is 8th magnitude HD 213472.













Image courtesy of DSS (Digitized Sky Survey)
GSC 790-523 nebula

Coordinates: 07 43 15 +14 48 05 (Gemini)

This anonymous nebula is surrounding 13th magnitude star and is 3' in size with fainter filaments continuing to south. Bright 9th magnitude star HD 62120 is just west of the nebula.














Image courtesy of DSS (Digitized Sky Survey)
TYC 3651-1162-1 nebula

Coordinates: 23 57 11 +50 41 55 (Cassiopeia)

Small (12' x 10') anonymous detail of a huge nebula complex. Brightest part is located just south of TYC 3651-1162-1. Forms a shape similar to that of an ear or Crescent nebula (NGC 6888).













Image courtesy of DSS (Digitized Sky Survey)
HD 41397 nebula

Coordinates: 06 06 59 +54 54 51.9 (Auriga)

Anonymous nebula complex with several individual patches visible in a 30' area. The brightest individual puff of nebulosity is located W of magnitude 10.6 star TYC 3755-802-1 with a size of ~4'.








Tuesday, 10 April 2012

Naked eye test - M44

I did a little test on the visibility of Messier 44 in Cancer without optical aid. As it is impossible to make identical observations of the same object on two different nights, the results are directional at best. More data will be added later on but it would seem that in order to see the cluster with the naked eye, the limiting magnitude in the region should be close to 5.0. This is slightly less than my previous estimate of 5.2 (Deep Sky Naked Eye Limiting Magnitude 2005 / Saloranta). Next in line would obviously be the visibility of M35 (unfortunately "out of season") and M13.

Based on personal experience, in order to see M44 with the naked eye from suburban location:
  • Delta Cnc (mag 3.9) needs to be visible with direct vision.
  • Gamma Cnc (mag 4.7) should be visible at least 50% of the time with averted vision.
  • Theta (5.4) and Eta Cnc (mag 5.3) will probably be invisible.

M44
Castor, Pollux, Mars and M44 barely visible in the pinkish hue of light pollution

How were the observations made?

  1. The same observing spot was used on all occasions.
  2. M44 at an altitude of 40 - 50°.
  3. The weather was very similar on all occasions.
  4. Dark adaptation (night vision) was limited to 5 minutes.
  5. The SQM-L reading was taken directly from M44 and mean value was taken based on 5 separate measurements.
  6. At 23.00 the city shuts down half of the streetlights on the small walking path leading to the observing spot used.

7.3.2010, 21.11 - SQM-L 17.70 (NELM ~4.85)- M44 invisible.
13.3.2010, 22.06 - SQM-L 17.98 (NELM ~4.99) - M44 fairly easily visible with averted vision.
13.3.2010, 22.36 - SQM-L 17.94 (NELM ~4.97) - M44 perhaps slightly more difficult than on the previous try.
13.3.2010, 23.06 - SQM-L 18.01 (NELM ~5.00) - M44 fairly easily visible.
13.3.2010, 23.36 - SQM-L 18.02 (NELM ~5.00) - M44 fairly easily visible.
13.3.2010, 23.56 - SQM-L 18.02 (NELM ~5.00) - M44 fairly easily visible.
14.3.2010, 21.36 - SQM-L 17.84 (NELM ~4.92) - M44 very difficult.


Naked eye limiting magnitude = (SQM reading - 8) / 2

The mighty few - the two missing NGC clusters

In 1863, G. P. Bond (director of the observatory at that time) published a list of 33 new deep sky objects discovered by astronomers who worked in the Harvard college observatory. These observers include George Phillips Bond himself (1825-1865), Phillip Sidney Coolidge (1830-1863), Horace Parnell Tuttle (1837-1923), and Truman Henry Safford (1836-1901). (As a side note, I'd like to note that in the 2010 book "Observing and Cataloguing Nebulae and Star Clusters" by Wolfgang Steinicke, there seems to be a typo regarding the age of Coolidge when he died. It says in the book that Coolidge "was born on 22 August 1830 and died in the civil war on 19 September 1863 being only 29 years old". Unless there are something wrong with the birth/death date, I'd say Sidney Coolidge died at the age of 33)

Bond's paper was published in the Astronomische Nachricten (No. 1453) but the paper had some quirks. First, the discovery of the two of our objects in questions NGC 2189 and NGC 2198 are credited as having been discovered by J. H. Safford. This is at least corrected (by whom?) in the copied version of the publication (J crossed and T added to the right side margin). The second one is, as everyone who's had a look at this particular dilemma, the position of the two missing NGC clusters in Orion. There are no coordinates for any of the clusters, only 1863 coordinates for the near by position stars! What a bummer. We know that the clusters were pretty certainly found with a magnification of 141 and field of view of 11'. Either there is something I'm not seeing here or there is something profoundly wrong with the original coordinates.


Object 7(a) & 7(b) - NGC 2189

"Two clusters, seen 1863 March 19 near two stars of the 10.11th magnitude, by J. H. Safford, with the Great Refractor [15 inch Merz refractor]. In Harvard Zones [IV]. Position of stars:

06h 04m 44.9s +01° 08' 37" (1863) = possibly GSC 131:1117
06h 05m 47.2s +01° 10' 02" (1863) = possibly GSC 131:1065

Not only are these two stars nearly 15' apart, there is no sign of any clusters in the area. It is also important to notice that Safford specifically mentions TWO clusters not a single one like the single NGC designation suggests. Safford's description "near two stars mag 10-11" is also fairly vague. Visual inspection of the region comes up pretty empty as well. 1908 paper by Pickering gives us coordinates of 06 12 22 +01 07 34 which is pretty much at the current non-ex position of NGC 2189. The asterisms discovered previously with the 15 inch refractor (1852-1853 for example) are pretty vague and are often very difficult to to discern from the background sky at all so in that aspect these clusters are a good match.


Object 8 - NGC 2198

"A cluster, see 1869 March 19, by J. H. Safford, between two stars in the following position. With the Great Refractor. In Harvard Zones [IV].

Star of 10.11 mag. 06h 06m 27.8s +01° 01' 10" (1863) = possibly GSC 131:870
Star of 9.10 mag. 06h 07m 12.7s +01° 00' 27" (1863) = possibly GSC 131:1266

What is between these two stars? A load of black space that's what! These two stars are separated by a mere 6'. Pickering's 1908 do not differ much from the current non-ex position of NGC 2198 just like with NGC 2189.


Simply from a visual observer's point of view, there is one possibility hanging in the air. A fairly good looking asterism can be seen more to the north, nearly in the middle of NGC 2189 and NGC 2198. The asterism is flanked by 9th magnitude HD 288493 and 10th magnitude HD 288534.

The position is however quite far away from the given positions of NGC 2189 and NGC 2198 and there is just one object - not three.

Unless someone takes a look at Safford's original observing logs like Dr. Harold G. Corwin suggest... I'm willing to go with the fact that these are nothing more than two very poor, uninteresting groups of few stars as suggested in the NGC/IC project home page. Sadly.

Johann Bode's three lost objects

The German astronomer Johann Elert Bode (1747 - 1826) published a list of 75 deep sky objects in 1777 in the "Astronomisches Jahrbuch" for 1779. Five years later, Bode published an updated (but sadly not corrected) list of 110 objects. Simply too many errors remained to make Bode's catalogs a hit like that of Charles Messier's. Luckily, even today some objects, namely M81 & M82 and M92, are still marked as being discovered by Bode. [4]

As with nearly all the deep sky catalogs, certain entries in Bode's catalog are shrouded in mystery, deception and romance. Well, maybe not romance but at least some good old fashioned mystery. Some objects are simply considered lost. The two asterisms in Bode's list are no longer even associated with Bode himself, even though he was the probably the first person to note these at least a hundred years prior to others.

To simplify things, the three objects presented here are marked as Bode 1 – 3.



Bode 1 (published in 1777) = IC 1434?

Original coordinates: 03 23 +57 30 (Ecliptic B1780.0)
Precessed coordinates: 22 09 08 +52 54 40 (Equatorial J2000.0)

Bode's first object is most commonly associated with the faint open cluster IC 1434 found at least by reverend Thomas Espin (1858 – 1934) in 1893 and added to the first Index catalog (1895) by J.L.E. Dreyer [1]. According to SEDS.org internet site by Hartmut Frommert and Christine Kronberg the cluster was "independently found by Espin in 1793" [2]. This is obviously a typo as Espin lived in the 19th not the 18th century. Still, no matter how you put it, IC 1434 just does not fit the bill.

Bode's coordinates do match IC 1434 very well. The only problem is how can an observer look for something in this region of the sky, namely Lacerta, observe IC 1434 and completely miss two other brighter and more obvious clusters: NGC 7209 and NGC 7243. Without knowing the specifics of Bode's telescope, apart from the focal length of 7 feet, it is a big guessing game but the aperture might have been around 2.7 inches (7cm). Telescopes during that time commonly had magnifications of over 100 and very poor optics. With the high magnification in mind, one might understand why Bode might have not seen the two NGC clusters. Still, just to loose the few remaining hairs from my head, he rediscovered IC 4665 which basically is as sparse and big as a cluster can get. So anything more we know about his telescope? We can at least compare his notes to those of Messier's:

M29
Charles Messier saw "A cluster of 7 or 8 very small stars"
Johann Bode saw "A nebulous star cluster"

M37
Messier: "Cluster of small stars"
Bode: "A vivid nebulous patch, in which no stars were recognizable" but later on "Around the new nebula there appeared many small stars in the 7-foot telescope"

M38
Messier: "Cluster of small stars in Auriga"
Bode: "A star cluster"

Bode, just like Charles Messier, failed to see individual stars from any of the globular clusters. At the same time, we can see from Bode's sketches he did manage resolved M67 (stars magnitude 9.6 and fainter) and M38 (stars magnitude 8.4 and fainter) [3]. This means his telescope much have reached at least 10th magnitude stars.

So how is it even possible he saw IC 1434? He mentions it as a "star cluster" so it seems he managed to resolve the object, whatever it was he was observing. With the statistics of IC 1434 being 9.0 magnitude and the brightest stars close to 12th magnitude it is fairly easy to say he did not observe IC 1434. Did Johann Bode use a different, larger aperture telescope in his discovery of the first object? Bode was appointed to the Berlin observatory in 1772 and became the director in 1786, so he must have had access to the observatory's telescope(s) if there every was a bigger one. Still, I think it is very, very far fetched to say Bode saw IC 1434 based simply on the fact that his coordinates are close to it. Even if he might have seen it, he probably would have described it as a "a nebula" or "a nebula without stars" rather than a cluster.

So what did Bode see? The only thing in the "tail of Cygnus" is of course M39 but this is already listed in Bode's catalog as number 75 and the location is correctly listed: "West near Pi at the tail of Cyg". With a bit of a reach, one could associate Bode's object as NGC 7243. This is east of Pi Cygni but no where near the tail or even in the constellation Cygnus. It would have probably been listed as "west of Alpha Lacertae" or something similar. Then again, Bode's original coordinates actually are in Lacerta, instead of Cygnus. Bode's own maps show the borders of both constellations nearly in modern form. Best bet in this puzzling case is that Bode independently found M39, poorly marked the position and then later added Messier's M39 in his list as well. Far fetched? Yes. Then it could be that he actually saw NGC 7243 but the coordinates are well off. So this issue will remain unresolved.



Bode 2 (published in 1777) = HD 1825 group

Original coordinates: 29 37 +45 55 (Ecliptic B1780.0)
Precessed coordinates: 00 22 51 +53 57 19 (Equatorial J2000.0)

In Johann Bode's description of Charles Messier's object number 29 on the night of December 5th 1774 he also mentions an object "in Cassiopeia a similar cluster with the stars Zeta and Lambda at the head west of it in an obtuse-angled triangle."

Little north of Bode's coordinates is a bright asterism of 7 stars brighter than magnitude 11. The brightest star is 8th magnitude HD 1825. This is obviously the grouping Bode was talking about and observed. The very same group is currently logged as Alessi J0022.7+5417 in the Deep Sky Hunters database for asterisms.



Draco 102 = Bode 3 (published in 1782), Bode's cluster, Kemble 2

Original coordinates: 279 30 +72 10 (Ecliptic B1780.0 and Equatorial J2000.0 for Dec)
Precessed coordinates: 18 19 26 +72 16 47 (Equatorial J2000.0)

Directly east of Bode's coordinates is an asterism some might know as "Mini Cassiopeia" or "Kemble 2". The nickname "Kemble 2" comes from Canadian Lucian J. Kemble (1922–1999) and he is well known by some from Kemble 1 / Kemble's Cascade in Camelopardalis. It is not known to me how this little group got the nickname "Kemble 2" but to be precise, there is no reason to do so. This is an original discovery of Johann Bode circa 1782, two centuries prior to Lucian Kemble. Of course asterisms don't have official names so anyone can call it whatever they want.



References:

[1] NGC/IC observers. Dr. Wolfgang Steinicke. 2010.
[2] http://seds.org/messier/xtra/ngc/i1434.html
[3] http://www.lsw.uni-heidelberg.de/foerderkreis/bode/images/atlas/tab30.jpg
[4] http://seds.org/messier/xtra/similar/bode1782.html

Wednesday, 4 April 2012

TYC 4948-53-1 group - The Virgo Diamond-asterism

Roger Ivester of the LVAS (Las Vegas Astronomical Society) has brought to my attention a tiny but dazzling little asterism in Virgo. Roger told me in an email that the group first made its appearance in an old Sky&Telescope magazine (May 1993) but has apparently evaded proper attention ever since. I usually don't get too excited about asterisms with such few members (they lack the visual impact at the eyepiece) but based on what I've seen so far, I'm sure this will be an exception. Not having looked at this group through a telescope yet, I'm fairly certain you, I or anybody won't be disappointed by its subtle beaty.

To be sure this was just an asterism, I contacted the big kahuna Matthias Kronberger and asked for his expert opinion on it. He used VIZIER for the proper motion data and came to the same conclusion I did using Aladin (PPMX-data). So, the chance of stars simply aligning like this in the sky might seem remote (4% according to Brosch) but none the less the group is, unfortunately, just an asterism despite having similar spectra. A shame!

Virgo Diamond courtesy of The Digitized Sky Survey
The asterism is located between Gamma (Porrima) and Eta (Zaniah) Virginis. The brightest star in the group is 10.7 magnitude TYC 4948-53-1 with other four being magnitudes 12.3, 13.2, 13.2 and 13.7 and respectively. What makes this asterism curious and stand out is the diamond or square-shape and its tiny size (50"). The separation between the stars is - on average - only 30" so good seeing conditions and higher magnification is required to resolve the four main components into individual stars. Seeing the 5th star may also require larger aperture. I'll personally try to observe this grouping over the upcoming weekend - despite the near full moon and medium low altitude of 28°.

On the night of 4th of April I went after the object like predicted. The conditions were everything but favorable: SQM-L showed 16.70 from Virgo (note that the meter most certainly had some interference from the nearby 94% moon) and 17.70 measurements from the opposite direction. Weather conditions were as follows: 70% humidity, air pressure 1022 hPa and temperature -2°C (28F). My trusty old 8" Orion DSE was selected for the task for the obvious reasons. It came as no surprise that the focuser was yet again nearly frozen solid and I'd have to use so force to get the things moving again.

TYC 4948-53-1 group with 8" Orion DSE @ 200x (6')
Anyway, finding the correct position using Uranometria was not difficult but seeing something was. I had to wait closer to midnight for Virgo to rise high enough for me to finally give the asterism a real go. At first I only noticed a fairly faint star in the correct position using Baader Hyperion Zoom @ 16mm (75x - 54'). This was no doubt the combined glow of the stars in the tiny asterism. Zooming in more, @ 8mm (150x - 27') I noted two stars very close together and then a few times now and again - with optimal averted vision - I could see the two fainter stars come out of the shadows and just as quickly vanish back there again. I had the similar effect using the 6mm Baader Ortho eyepiece providing 200x (6'). Seeing two 13.2 magnitude stars under such abysmal conditions was a great victory and the asterism reminded me of Theta 1 Orionis cluster (Trapezium) buried inside the hazy heart of Orion nebula. This object is surely worth a visit and has a calculated total magnitude of (using NOMAD data) 10.4.