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Classic Rich Field

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#201 Millennium

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Posted 25 March 2018 - 06:45 PM

Not sure if this will work, link to Hyades Proper Motion animation courtesy Jos de Bruijne:

 

https://twitter.com/...0303877/video/1

 

 

MT


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#202 AllanDystrup

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Posted 30 March 2018 - 10:00 AM

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The Coma Berenices Moving Group

    

    

     It’s around midnight in mid-March (2018-03-20, ~24:00 Local, UT+1), and I have been out observing the close by Canes Venatici I galaxy group in the Local supercluster, stretched out as a Local Sheet (“Spring Milky Way”) of galaxies along ~12h30m R.A.: from the M81–CVn groups in the north to the  M83–CenA  groups in the south.

 

     Before I head for the bunk tonight, I decide to finish my small winter project of observing our nearby moving stars groups, by zooming in on the Coma Berenices cluster, also conveniently located tonight at ~12h30m R.A. close to the meridian. This loose group of semi-bright stars (~40 members of 5m-10m) is seen dangling like a filigree pendant necklace below Gamma Com.; It is a splendid sight in the 6° FOV of my 10x56mm bino, and still impressive at 23x and ~ 3.6° FOV in my small 55mm Vixen refractor. Although there’s a high haze of thin Cirrus clouds, the central part of the Coma B. group is easily seen as more than a dozen, bright (5m-8m) stars, predominantly being yellow type A-F main sequence dwarfs.

 

     The Coma Berenices star cluster (aka. Mel 111) consists of a total of ~40 relatively bright (5m-10m) stars with a common proper motion towards the North-East (-12.5, -9 mas/yr), and a radial velocity of ~ 5.5 km/s. The distance to Coma B. is ~86 pc (280ly), almost twice the distance to the Hyades (151 ly), but only half way out to the Pleiades (444 ly). Coma B. is also intermediary with respect to age (450 Myr), but this time with the Pleiades as the youngest (100 Myr) and the Hyades as the older brother (800 Myr).

 

 

ComaB..jpg
*click*

 

-----

 

     It has been a fun, small project: researching, observing and sketching the several moving groups of stars in our solar neighborhood. The more I’ve researched, the more the kinematic stellar cluster structures have turned out to be a complex of many smaller overlapping heterogeneous aggregates of near and far, thin and thick galaxy disc stellar streams that happen to align in moving groups as seen from our solar system, at this particular point in space-time. To paraphrase the classic Adventure game (the mother of all modern computer games):

 

YOU ARE IN A MAZE OF TWISTY LITTLE PASSAGES, ALL DIFFERENT.
YOU ARE IN A LITTLE MAZE OF TWISTING PASSAGES, ALL DIFFERENT.
YOU ARE IN A MAZE OF TWISTING LITTLE PASSAGES, ALL DIFFERENT.
YOU ARE IN A LITTLE MAZE OF TWISTY PASSAGES, ALL DIFFERENT.
YOU ARE IN A TWISTING MAZE OF LITTLE PASSAGES, ALL DIFFERENT.
YOU ARE IN A TWISTING LITTLE MAZE OF PASSAGES, ALL DIFFERENT.
YOU ARE IN A TWISTY LITTLE MAZE OF PASSAGES, ALL DIFFERENT.
YOU ARE IN A TWISTY MAZE OF LITTLE PASSAGES, ALL DIFFERENT.
YOU ARE IN A LITTLE TWISTY MAZE OF PASSAGES, ALL DIFFERENT.
YOU ARE IN A MAZE OF LITTLE TWISTING PASSAGES, ALL DIFFERENT.
YOU ARE IN A MAZE OF LITTLE TWISTY PASSAGES, ALL DIFFERENT.

 

     I’ve only scratched the surface of the kinematic stellar structures of our Local Bubble; you can spend hours trying to map out the maze of little twisting branching streams around us, all different yet in some ways all the same-- and it’s fun and educational, but complicated. I may return to the USC-UCL-LCC Stream, the Hercules Stream and more moving groups later this year, but for now, I plan to keep my focus on the project of rich-field galaxy observing. I hope Millennium will share his research and discoveries here, and in the meantime, here's a couple of good, recent sources for further studies of moving groups in our Local Bubble:

 

CB-01.jpg
*click*

CB-02.jpg
*click*

 

 

Allan
 


Edited by AllanDystrup, 30 March 2018 - 10:12 AM.

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#203 Millennium

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Posted 03 April 2018 - 09:44 AM

Thanks for the clarification, Glenn!

 

I just added the Galactic Coordinate Directions & Designations (red)to this velocity chart of the Gould Belt to go with my Kinematic Mapping of the Orion Spur, and it seems to agree with your citation!

 

Looking down from Galactic North (Z axis) with East (~Cepheus, 270°) along the Y axis ahead, and West (~Vela, 90°) behind, and Galactic Center to the Right (~Sco-Cen, 0°) and Antiward Left (~Orion, 180°) we observe the Gould Belt (and Orion Spur) spinning CCW.  ALSO CCW looking from the West (~Vela, 90°) toward the East (~Cepheus, 270°)!

 

Then I added the Orion Arm Magnetic Field vector (blue) to show that the Gould Belt (and I assume WHOLE Solar Neighborhood and Orion Arm) obeys the Right-Hand Rule of Electrical Engineering.

 

Millennium

 

The "ellipse has an aspect of about 1.5:1, with the long axis oriented in the azimuthal direction, or V axis, or in the direction of Galactic longitudes 90/270.

 

"This elliptical pattern is an epicycle, and its size scales as the magnitude of the peculiar velocity. For instance, for our Sun's peculiar velocity of about 20 km/s, its epicyclic motion traces an ellipse having a radial (along the short axis, pointing toward the Galactic center/anticancer) extent of something like 1,000 l-y (and hence some 1,500 l-y on the long axis.) If a star lying at the center of that ellipse had a circular Galactic orbit and hence zero peculiar velocity, our Sun would 'orbit' that star on its epicycle, in a CCW direction as viewed from above (N of) the Galactic plane.

 

"At the solar circle, which is the Sun's distance from the Galactic center, an object completes one circuit about its epicycle in about 2/3 of a Galactic orbit. This means that as viewed in an inertial frame, an object's Galactic orbit traces out an almost closed tri-lobed rosette, where three epicycle periods occur in two orbits about the Galaxy. Where the peculiar velocity is greater, the epicycle, as noted, is commensurately larger, but the epicycle period remains the same. And so the rosette traced out has a larger radial excursion.

 

"For objects or structures which have much the same galactocentric distance for the guiding centers of their epicyclic ellipses, they will remain in the same general vicinity, oscillating about on their own individual epicycles. If an object has its guiding center lying at a larger galactocentric distance, it will gradually trail behind due to differential galactic rotation. For such nearby objects/structures as the stellar streams considered here, where the peculiar velocity does not exceed about 50 km/s, the epicycle motion keeps them in the general vicinity over considerable intervals of one, or two, or even more galactic orbits. That is, these objects do not simply keep separating over time on a gradual arc about the galaxy; they periodically separate and close distance.

 

"The epicycle approximation for Galactic orbits is reasonably good when the radial excursion does not exceed about 1/10 the galactocentric distance for the guiding center. For instance, at the solar circle of 25,000 l-y, an object orbital radial excursion of 2,500 l-y, resulting from a peculiar velocity of about 50 km/s, is reasonably well enough described by epicycle theory.

 

"Recall the 1.5:1 ellipse ratio for a Galactic epicycle. This results from the gravitational potential in which additional mass is enclosed with increasing galactocentric distance.

 

Attached Thumbnails

  • GouldVelocitiesMagEWNSsmall2.jpg

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#204 AllanDystrup

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Posted 10 April 2018 - 03:53 AM

.

 

6 Mpc - 20 Mly  Step 2: The Local Supercluster.
The M81 - CVn – M83 – CenA groups, 
plus the M101 and Leo Groups

 

 

M101-LEO I - 01.jpg

*click*

 

M101-LEO I - 02.jpg
*click*

 

 

M101-Group-Map.jpg

*click*
 

 

To be continued

Allan


Edited by AllanDystrup, 11 April 2018 - 02:28 AM.

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#205 AllanDystrup

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Posted 10 April 2018 - 04:12 AM

.

The M101 Galaxy Group

 

 

     Let’s start from the north, with the largest member of this group: M101.It’s the beginning of April (2018-04-09) one hour past midnight local DST (UT+2), and I’ve relocated my small Vixen FL-55S refractor from my suburban backyard, out 1km north to a semi-dark place (SQM 19.7 / NELM 5.9m) with a free view across open fields towards the south. Spring has arrived with the start of April; a high pressure over Eastern Europe is pulling warm winds from the Mediterranean up over Scandinavia with temperatures rising to ~20°C. The frogs and grass snakes have started migrating from their hibernation to the surrounding ponds, the great tit and wren and nuthatch are all singing, and the queens of bumble bees are buzzing busily in the blossoms.

      
     The temp here past midnight is still a comfortable 8°C, and it’s calm with no moon, quiet apart from the soft hooting of a distant night owl. The warm winds however, have arrived with a high haze on its coattails,  which reduces the transparency significantly towards the horizon, and this is bad news as my main target this morning was M83 to the far south, at just ~4° altitude. Try as I may, I can’t see it, so instead I turn my telescope towards M101, which tonight is sailing high up overhead, at ~80° Alt.

 

 M101-Group-WHITE-S.jpg
*click*

 

 

     The star hop to M101 (aka the “Pinwheel galaxy”) is easy: from Alcor-Mizar, east past a nice cascade of ~5m stars (81-83-84-86 UMa), and then M101 is just 1½° SSE of 86 UMa. I can’t spot it in my 10x56 bino, neither can I detect it with certainty in my 60mm f/4 finder (6.3x mag). The galaxy is however seen with averted vision at 23x in my 55mm refractor, where it shows up as a relatively large (~4’), very faint hazy spot, best detected by gently moving the scope a little back/forth in R.A. The observation is confirmed at 30x magnification, but I can detect no details at all in the faint fuzzy. M101 is the third largest M-galaxy by appearance on the night sky, but its low surface brightness (~14.8m) makes it difficult to observe at low magnifications, if the transparency is not excellent. I’ve detected it @ 24x using my 80mm refractor, but for a detailed study I needed to push to 110x using my R2 live video “eyepiece” (see: https://www.cloudyni...-4#entry7383759).

 

     For observations of the next two galaxies in the M101-group, we have to move 20 days back in time, to 2018-03-20.  -- A string of nights, with no astronomy:

 

Settling, melting
on mother's coffin --
April snow

 

  

  
     Back then, I was out on a cool and calm evening (21:00 Local UT+1) to sweep up the other two Messier galaxies in the M101-group: M51 and M 63. The seeing was above medium (6/10) and the NELM was good (5.6m), but the transparency was varying 4-5/7, with thin cirrus degrading the view towards the horizon (not a problem though at ~53° Alt., where my next galaxies are located). The star hop for M51 (aka the “Whirlpool galaxy”) takes me from Alkaid (Eta UMa) due W to 24 UMa, then ~2° SSW to a triangle of 7m stars, with M51 just W of the S apex. I can’t detect M51 with my 10x56 bino tonight (but I have seen it previously on an excellent night, using my 10x50mm classic Zeiss bino). In my 60mm finder, M51 is seen with averted vision @ 6.3x as a faint spot. In the 55mm refractor, I can hold M51 with direct vision at 23x; It shows a faint halo, a brighter center and a slight N-S elongation (which is the combined light of N5194 + N5195). Again, for more detail see my previous observation here: https://www.cloudyni...sier/?p=7345940).

    

    
     Finally, on March 20. 23:30, I close the observation night with a look at M63 (aka the “Sunflower galaxy”). Again, the star hop is straight forward: from Cor Caroli (α CVn), NE almost 5° to a T-shaped asterism including the line of 5-6m stars: 19-20-23 CVn. From 19 CVn it is then simply 1° due N in DEC to M63. This galaxy is glimpsed with indirect vision in my 10x56mm bino, where it reveals an elliptic shape with an E-W orientation. In the 60mm finder, I can hold it with direct vision, and it shows a stellar core in the nucleus. In the 55mm refractor, the galaxy is a beautiful sight, showing with direct vision the “classic” traits of a grand galaxy: a faint halo, a gradually brighter nucleus plus a clear stellar core. Woderful! For more details, I refer to my previous observations of the Sunflower:
https://www.cloudyni...ier/?p=7572697 and https://www.cloudyni...sier/?p=7572701.

 

    

Allan



#206 Organic Astrochemist

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Posted 11 April 2018 - 01:25 PM

.

Canes Venatici I Galaxy Group (13 MLY)

 

    

    

     It’s an early evening in mid-March (2018-03-20, ~21:30 Local, UT+1). It’s calm and cool (-1°C) with a 13% illuminated waxing sickle moon peacefully grazing the NW horizon, on its way down under the eiderdown. The seeing is medium (5/10), and the darkness in my suburban backyard is fine tonight (SQM 19.2 ~NELM 5.6), but the transparency is down at 4/7, due to a light, high cirrus haze. Not optimal at all for galaxy sweeping, but never the less I’m out to see what I’ll be able to catch with my small instruments: a 10x56 Zeiss bino plus a FL-55S f/8 Vixen refractor.

     

     My plan for tonight is to  continue my first sweep of the “Spring Milky Way” of galaxies, which I started a couple of days ago with a focus on the nearest galaxy groups (15-20 MLY distance) in the “Local Sheet” defining the supergalactic equator. At this time of the year, this Local Sheet is seen stretched out as a lumpy band from UMa in the north across CVn and down to M83-CenA in the south, roughly along the 12h30m R.A. great circle, which will be crossing the Meridian at  ~01 AM Local in the morning.

    

     In my first observation post for this project I described the M81 Galaxy Group 12 MLY away in the UMa-Cameleopardalis area, and tonight I’ll be moving south to the Canes Venatici I galaxy group, located at roughly the same distance (~13 MLY).

         

attachicon.gif CVnI GG.jpg

*click*

    

    

     I start with the M106 galaxy in the NW “corner” of the CVn constellation, bordering on UMa. The star hop takes me from Phecda (γ UMa), E to the line of 5-3 CVn, then due S a good 1½° in DEC. M106 can be glimpsed as a hazy spot in my 10x56mm bino, using indirect vision (and knowing the exact location of the galaxy). In my 60mm f/4.2 Zeiss finder with a ATC H-40mm EP (6.3x mag.), I can hold the galaxy with direct vision. Finally at 23x in the small 55mm refractor, M106 shows up as a hazy ellipse directed SSE-NNW, with a slight brightening towards the center, but without an obvious stellar core. For more detail, see my observations of M106 at higher magnifications using my FL-80S/640mm refractor. This is posted in the “Classic Messier” thread:
     Muggler glass eyes: https://www.cloudyni...sier/?p=7627030
     Live Video ccd/lcd : https://www.cloudyni...sier/?p=7627038

    

     Next I proceed to M94 (the “Bull’s Eye”) galaxy in Canes Venatici. I locate this galaxy by starting from the position between Beta (Chara) and 9 CVn, then slowly panning 3° due E in R.A.  M94 is glimpsed in my 10x56mm bino, but obviously seen with direct vision as an unstructured faint round haze in my 60mm finder at 6.3x. M94 shows up in the 55mm refractor at 23x using direct vision as a stellar core in a bright nucleus embedded in a faint, round comet-like halo. For more detail on this object, see my observation of M94 at higher magnifications using my FL-80S/640mm refractor in the “Classic Messier” thread:  https://www.cloudyni...sier/?p=7231429

    

     Finally I proceed to M64 (the “Black Eye”) galaxy in Coma Berenices. I locate this galaxy by starting from δ Leonis (Zosma), then slowly panning 3° due E in R.A., first below and past the Coma-B moving group, until I hit upon the ~5m bright orange star 35 Coma B.  I have a hard time spotting M64 in my 10x56mm bino (the eyepieces have started to dew up…); I won’t log the galaxy as seen in the bino, but I am able to just glimpse it as an unstructured faint haze at 6.3x in my 60mm finder. The galaxy is clearly seen in my 55mm refractor @ 23x, best when using averted vision and slowly sliding the scope a little back/forth in R.A. It is slightly elliptic with an orientation ESE-WNW. I can detect no structure in the galaxy. For more structure in this object, see my observation of M64 at higher magnifications using my FL-80S/640mm refractor in the “Classic Messier” thread:  https://www.cloudyni...sier/?p=7231422

 

 

attachicon.gif CVnI GG - Black-S.jpg

*click*

    

    

PS:      I also looked for the two relatively bright NGC galaxies in the CVn I group: 4490 (Cocoon, Arp269) and 5005; Unfortunately the high haze had at this time of the night increased a bit, so I was not able to detect these galaxies; For a previous observation of N4490, see my post in the “Classic Best NGC” thread: https://www.cloudyni...-3#entry7857893.

 

Allan

Hello Allan.

Great observing project. I'm doing something similar.

Although there are many nonmember galaxies projected onto the same area of sky as the local sheet, there isn't another overlapping sheet. In this way, observing such a large structure as the local sheet is easier than observing some nearby galaxy groups: in addition to individual nonmember galaxies, some galaxy groups have overlapping galaxy groups. I think a great deal of humility is needed here and even the pros acknowledge mistakes in galaxy group membership are common.

I think that this is happening in the constellation of Canes Venatici.

You note that the CVn I group lies at distance of 13 Mly (~4 Mpc) and yet M106 lies at a distance of 25 Mly (7.6 Mpc), a similar distance as M101 and M51.

I strongly recommend this article by Brent Tully

If you look at his Figure 7, you can see how busy it is in the constellation of Canes Venatici. the galaxy groups, defined as virialized dark matter halos, of M51 and M106 clearly overlap. These are gravitiationally bound to each other and to many other galaxy groups, but their dark matter halos have not yet merged. Therefore he calls this a galaxy association. The M51 association is the largest nearby association and contains 52 galaxy groups (often with only one galaxy) and over 100 visible galaxies.

The picture that emerges to me is that M51 is not just a pretty face. It is the dominant galaxy in a large collection of galaxy groups. Presently, I am working my way through the many wonderful galaxies to observe there.


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#207 AllanDystrup

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Posted 12 April 2018 - 02:40 AM

.

Hi Organic Astrochemist,

    

     Thank you for your comments! -- you're touching on a central issue in trying to classify (characterize, group,) and thereby understand astronomical objects, be that nebulae or star clusters in our own Milky Way or more distant assemblages of galaxies: 

  • to what extent are these chance alignments of evolutionary unrelated objects, just coincidentally coming together, being - so to speak - "piled up" by the random perspective in space-time of our solar system, or perhaps by secondary gravitational resonances in larger scale astronomical structures?

versus

  • to what extent are their appearance caused by a common origin, a joint genesis yielding a curret global morphology and interaction, which can be explained by known astrophysical processes?

    

     I'm encountering this question of structure vs. evolution again and again here in my Rich Field project, for example in my study of molecular clouds in the Orion-Monoceros complex, and last in my observations of moving groups in our immediate solar system neighbourhood.

 

     For the stellar streams, although I observed and described these as co-moving groups, I tried to sum up the complexity of origin (in post #202 ) as: "the kinematic stellar structures of our Local Bubble ... being in reality a complex of many smaller overlapping heterogeneous aggregates of near and far, thin and thick disc stellar streams that happen to align in groups as seen from the solar system at this particular point in space-time". The verdict on common origin and evolution of the separate parts of these moving groups is still out, but we're getting closer with the data from GAIA, -- as also Millenium is researching.

 

     It's evident, that much of the same complexity in classification and thus the same structure vs. evolution discussion is relevant with respect to the extent and distribution of galaxy groups and superclusters, and it seems that the Tully-Kourkchi article from 2017 does provide a breakthrough for delineating cluster extension based on a halo mass function of aggregates in the Local Sheet. Very interesting, thank you for bringing this up, and I'm following your exploration closely in your "Observing galaxy groups and galaxy associations" thread.

 

    For my own small spring galaxy sweeping project, I have chosen a "beginners wide-field approach", zooming out on an approximate  distance  ladder as a rough means of grouping the galaxies. The 4 steps on this ladder is enough to yield a perspective to the Local Supercluster (sheet) as we can observe it in the "Spring Milky Way of Galaxies" along R.A.12h30m:

 

½ MPC  1.5 Mly  0: The Milky Way.  
                   Incl. its two Magellanic Cloud irregular spirals
                   and many spheroidal dwarf galaxies.
2 Mpc - 5 Mly   1: The Local Group
                   The Milky Way - Andromeda - Triangulum galaxies with their satellites, 
                   plus the Sculptor Group (N55 at ~10 Mly).
6 Mpc - 20 Mly  2: The Local Supercluster.
                   M81 - CVn - M83 CenA groups, 
                   plus the Leo Groups (several Messiers at ~40 Mly).
20 Mpc  70 Mly  3: The Virgo Supercluster.
                   The UMa  Coma -Virgo groups, all in the background at ~50 Mly.

 

     This coarse approach is however *not* enough for a more precise and up-to-date astrophysical characterization of the seperate galaxy groups, and for that I think your observations and explanations in the "Observing galaxy groups..." thread is a perfect supplement and corrective! I for one will follow this closely, and I hope you'll also contribute to my beginners thread with comments and corrections, when I over-generalize or step into the trap of characterizing groups more from classic structure than from modern astrophysical mass-velocity constraints.

 

Allan


Edited by AllanDystrup, 12 April 2018 - 02:59 AM.

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#208 Organic Astrochemist

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Posted 13 April 2018 - 03:51 PM

Hi Allan,

To me, your posts affirm the central role of distance in astronomy and how the availability of increasingly accurate intragalactic and extragalactic distances can be useful for amateurs.

 

"Why is the moon brighter than the stars daddy?"

"Because the moon is closer and the stars are further away."

 

Any galaxy observation that one enjoys is a good observation. When viewed in isolation, perhaps the distance matters less than brightness, morphology and visible details. But when galaxies are viewed in groups or compared it is the distance that allows one to begin to understand how things are not always as they appear. M106 doesn't appear bigger or brighter than M94 or M64 because it is at almost twice the distance -- but it is.

 

Amateurs don't talk about galaxies as nebulae. I think they will increasingly talk about galaxy distances.


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#209 AllanDystrup

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Posted 14 April 2018 - 09:51 AM

.

The Leo Galaxy Groups.

    

    

     It’s a spring midnight in mid-April (2018-04-11, 23:30 Local DST UT+2). There’s a high, thin Cirrus haze reducing the transparency (4-5/7) and a medium wind causing a slightly wavering seeing (8/10), but I can just glimpse M66 in the Leo Triplet as a faint fuzzy, using my Zeiss 10x56 bino, so I plot the course for the galaxies in the LEO Galaxy Spur tonight. Steady as she goes…

    

Leo Galaxy Spur Map.jpg
*click*

    

    

TBC

Allan


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#210 AllanDystrup

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Posted 14 April 2018 - 10:12 AM

.

Leo Galaxy Spur - continued.

 

 

     My first stop is the Eastern Leo Triplet subgroup consisting of M66-M65-N3628. The star hop takes me from Theta Leonis, 2° due S to 73 Leo, then 45’ due E to the 7m star HD98388. In my C60 viewfinder with 40mm EP (6x), M66 is seen – best with averted vision - as an obvious, but faint hazy oval, with what seems to be a stellar core; M65 is barely glimpsed in the finder with averted vision, close by to the W.

    
     In the FL-55S refractor with 32mm EP (23x), the whole triplet is nicely framed in the central 1° part of the ~3.6° FOV: M66 is now seen with direct vision as a SSE-NNW oriented ellipse, with a 10m foreground star (TYC 861-1197-1) at the N border of the galaxy (this is what showed up as a “stellar core” at 6x in my finder). The galaxy has a brighter nucleus, and at moments I think I can glimpse a true stellar core in this, using averted vision. The companion galaxy M65 is seen close by (~20’) W of M66, forming an equilateral triangle with M66 and the 7m star (HD98388) to the N. M65 is fainter than M66, I can only detect it with averted vision, where it shows up as a faint N-S oriented hazy streak without any further details.

    
     The third member of the Eastern Leo Triplet: NGC 3628, is located at the center of a “T”-shaped asterism formed by 4 small 10m stars, just NE of HD98388. I take some time and effort to try seeing it, but it doesn’t yield to my observing tricks. It is drowned out tonight by the high haze and the LP (I've marked its position with a small dotted line on my drawing). For a close-up view of the Leo Triplet, see my post #20 in the “Classic Messier” thread: https://www.cloudyni...sier/?p=7063290

    

- - - - - - - - - -


 

     It is now half an hour past midnight as I slowly pan my 55mm refractor from the Eastern Leo Triplet 8° due W in R.A., where I get the Western Leo Triplet subgroup in the FOV: M105-M96-M95. I can’t with certainty detect them @ 6x in my 60mm finder, but they can all be glimpsed @ 23x in the 55mm refractor. It helps knowing the exact positions of these faint fuzzies, and then taking the time to patiently let their light integrate at the peripheral part of the retina.

     
     M96 and M95 both appear somewhat elongated in a roughly SE-NW direction, while M105 is clearly round. The brightest galaxy is M96, which also shows a faint core, while the two other galaxies show up as mere faint halos without structure.

 

LEO Galaxy Groups - BLACK-S.jpg

Eastern Leo Triplet: [N3628]-M66-M65                Western Leo Triplet: M105-M96-M95

*click*

    

    

     The two Leo Triplets both belong to the close by Leo Spur of galaxies at ~10 Mpc (33 MLy), which is streaming at ~320 km/s together with our Local Sheet towards the Virgo Supercluster attractor. There are more distant (and hence fainter) groups of galaxies in the Leo Cloud in the background (>16 Mpc or 53 MLy), which are also being pulled towards Virgo, but from the “back side”, and hence approaching us. As Tully notes in his article from May 23. 2017: “The takeaway for the present is that projection confusion can be severe because of velocity streaming, but distance information is becoming increasingly useful as a discriminant.”

    

     Here’s a figure from that article showing the major galaxy groups in the foreground Leo Spur (top) as well as in the background Leo Cloud (bottom). The two large blue circles include our two Leo Triplets of M-galaxies.

    

Leo Spur-Group.jpg
Galaxy Groups within 3500 km/s
E. Kourkchi & R.B. Tully, May 23 2017, Univ. of Hawaii

    

    

Allan


Edited by AllanDystrup, 14 April 2018 - 01:10 PM.

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#211 AllanDystrup

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Posted 23 April 2018 - 03:17 AM

.    

STEP 3:  The VIRGO Supercluster ~ 20 Mpc (60 Mly)
“The Spring Milky Way of Galaxies”

    

    

     It’s a couple of warm midnights in late March (2018-04, 19-20), and I’ve dedicated these for sweeping up the brightest Messier galaxies in the distant Virgo supercluster.  We’re now climbing the distance ladder:

  • From step 2, 20-30 Mly:   our Local Supercluster, including the M81-CVn-CenA Local Sheet
                                             
    with the M101 and Leo spurs.

     
  • To     step 3,  ~60 Mly:     the Virgo Supercluster, incl. the sheet of UMa – Coma-Virgo galaxy groups.

    

Step 3 - Virgo Supercluster Map.jpg  

*click*

    

    

     Doubling the distance makes the galaxies considerably smaller and fainter, so for this study I plan to supplement my small Vixen FL-55mm refractor with its FL-80mm big brother (still in rich field mode); I’ll use the 55mm to frame a wide view of the Coma-Virgo Cluster in two fields of ~4° FOV @ 23x magnifications; And then I’ll fill in the galaxies on my drawing, stepping up to the 80mm 2½° FOV @ 34x magnification, -- which will still provide rich views with several galaxies in each field when sweeping the Virgo cluster.

    

        I’ve recently done a census of the Messier galaxies in the Virgo Cluster using my Vixen FL-80S f/8 refractor at high magnifications, so I know the star field pretty well, which of course is a great advantage when star hopping to and identifying the targets.  Here’s the summary from my previous high magnification Messier scan, plus my shopping list and some observation notes from my current rich field sweep:

    

Virgo Cluster Table.jpg

*click*

 

Virgo Cluster 1:  “The Wall”: https://www.cloudyni...sier/?p=7164492 (E:M60,59,58 – W: M87,86,84)
Virgo Cluster 2:  “The Hook”:  https://www.cloudyni...sier/?p=7212107   (M89, M90, M91, M88)
Virgo Cluster 3 :  “The triangle”:  https://www.cloudyni...sier/?p=7219387  (M100, M98, M99)
Virgo Cluster 4: “The Outskirts” :  https://www.cloudyni...sier/?p=7223579  (N:M85 - S:M49, M61)

      

   

 

     There’s a high pressure over the Baltic Sea pulling warm Mediterranean air from the SE up over Scandinavia, resulting in high day temperatures (up to 25°C), and even a comfortable 10°C here one hour past midnight local DST (UT+2). As is however often the case in spring, the humidity is also high (currently ~90%), but with the dew point at 9°C, that is no problem for the telescope; – It does however result in a thin high haze, which poses a problem especially the first midnight, where I’m out with the 55mm to draw the wide field view; The stellar field is easy enough to draw (down to at least 11m), but I have a hard time seeing the galaxies, and only The Monster elliptical M87 is easy to spot in the 55mm, dangling like a pendant necklace below the 8.7m foreground star HD108915 seen in projection close to the center of the Virgo cluster.

 

  

     Also, on the first midnight, the sky glow is significantly higher (SQM 18 / NELM 5) than on the second night (SQM 19.6 / NELM 5.8), which makes a big difference for galaxy visibility. Actually the second night turns out to be a great opportunity for sweeping up the bright Messiers in Virgo, and in the 2h I’m out observing, I succeed without major effort in seeing all the galaxies I had planned for this rich field project; I have purposefully excluded the faintest as well as the most outlying ones (such as M91, 88, 85, 49, 61), as I just want to get a “wide field feeling” for the Virgo  Supercluster core, as it is located in the Spring “Milky Way of Galaxies”.

    

    

Virgo Cluster Shopping List.jpg

*click*

    

    

To be continued...

Allan


Edited by AllanDystrup, 23 April 2018 - 06:03 AM.

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#212 AllanDystrup

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Posted 23 April 2018 - 03:38 AM

.

The VIRGO Supercluster,
continued...

    

    

     My ”Star Gate” to the central part of the Virgo Cluster is the λ-asterism with 4.9m Rho Virginis in the center; from Rho I pan straight North in DEC almost 1½°, where I get the galaxy pair M60 - M59 right in the center of the FOV. In the 80mm refractor @ 34x, M60 is obviously seen with direct vision (DV) as a SSE-NNW elongated hazy ellipse, gradually brightening to a round core (the elliptic shape is actually a combination of the light from the E2 galaxy M60 + the small SAB companion NGC4647 to the NNW). The E5 galaxy M59 is found less than ½° W of M60; it is best detected with averted vision (AV), and here seen as a fainter hazy spot, slightly elongated S-N and with a bright stellar core.

      

     From the galaxy pair M60-59, I now start panning further west in R.A. along “The Wall”, first ~1° to the SAB galaxy M58 at the E tip of a kite-shaped asterism. The galaxy is glimpsed in DV, but best studied with AV; there’s a small (~11m) star just to the NE of the galaxy, which is slightly E-W elongated. From M58 I now continue to pan W in R.A. ca 1½°, to an axe-shaped asterism where I find the monster E0 galaxy M87 at the N tip of the axe. It is obvious in DV, round with a brighter core. This supergiant elliptical is at the gravitational center of the Virgo Cluster, and is one of the most massive galaxies in the local universe. Like a cosmic Death Star it harbors a supermassive black hole at its AGC core, which shoots out a giant jet making it a bright radio source (Virgo X1). It is guarded by many satellite galaxies plus a swarm (~12.000) of globular clusters; -- for comparison our Milky Way galaxy has <200 GCs. Continuing from M87 along “The Wall” a good 1° up NW, I finally arrive at the pair of ellipticals: M85 – M84. Both are seen in DV as hazy round spots with stellar cores, M85 a little elongated SE-NW.

    

     I now return to the middle of “The Wall”, to the tip of the kite-asterism at M59; from here I follow a line of 9m stars stretching 1° up N. This forms the base of “The Hook” of galaxies in the Virgo Cluster. To the W of the center of this line I find the elliptical M89, and just to the N of the tip of the line is the mixed SAB spiral M90.  Both show up as faint and round-ish spots, best seen with AV. M89 is stellar with DV. The observation of M89-M90 is confirmed at 43x (CZJ O-25mm).

    

     Finally I point the 80mm refractor at 60 Com, which is part of ”The T” (triangle) -asterism I use to locate spiral SA M99 (at the base of the “T”) and mixed SAB M100 (NE of the E tip of the “T”). At 23x both are glimpsed with AV as faint round hazes, and again confirmed at 43x (O-25). This completes the night’s sweep of the brighter Messier galaxies in the core of the Coma-Virgo cluster.

 

 

Coma-Virgo Cluster WHITE-S.jpg

*click*

             

Coma-Virgo Cluster BLACK-S.jpg

*click*
    

 

Virgo Cluster Association.jpg

*click*

 

 

Allan


Edited by AllanDystrup, 23 April 2018 - 05:59 AM.

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#213 Millennium

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Posted 23 April 2018 - 01:10 PM

There is no (Catholic) Cosmic Expansion. Tully et al, for example, misrepresent the Virgo Cluster as a sausage, extended along the line-of-sight, about five times longer than it's girth. Their apparent 'Laniakea Supercluster' also, is an aberration caused by a worse (repeat-overlay) false computer-algorithm warping of both the topology and velocity-fields of our local Superclusters.

 

When you contract this false mapping, by about a factor of five along the line-of-sight, you begin to get a picture of what we actually observe (without computer-manipulated distortion) -- the actual local Supercluster topology: http://www.atlasofth...com/nearsc.html

 

 

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  • Superclusters.jpg

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#214 AllanDystrup

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Posted 24 April 2018 - 02:08 AM

Millenium,

 

     The atlasoftheuniverse image you're showing plots the galaxies out to 500 Mly. It's a good representation, but I haven't taken this step on the cosmic distrance ladder yet in my survey. The data in the atlas picture seems to come from the revised Abell catalogue and Anthony Fairall's research on large-scale structures including voids (early 1990'ies).

 

     My rich field galaxy observations up till now have covered the local universe within ~70 Mly. It includes our Local Supercluster and the neighbouring Virgo Supercluster. I've been reading the Astronomical Journal articles by Tully et al on the local group (2013), galaxy groups (2015) and cosmic flows (2016). These are based on positional and kinematic data from among others Spitzer, HST and the 2MASS catalog. I find Tullys attempt to quantitatify structure associations based on zero-velocity surfaces of halos to be a fresh new approach with great potential. Also, attemts to computationally simulate collapse of regions of mass into structures is challenging, yes, but it seems to me that Tully acknowledges the difficulty in modelling the real world this way.

 

     In the next step of my galaxy Odyssey I'll be targeting the large scale structures out to 500 Mly. I'll base my understanding of this on among others the Astronomical Journal "Cosmography of the Local Universe" by Tully et al., which I find is an oustanding survey.

 

Allan


Edited by AllanDystrup, 24 April 2018 - 02:43 AM.

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#215 AllanDystrup

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Posted 05 May 2018 - 05:55 AM

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The Ursa Major galaxy group.

    

    
     It’s an early morning in late spring (2018-05-04, ~02 AM Local DST, UT+2). The temperature tonight is down at a fresh 4°C (dew pt. ~3°C), but the days have already turned from spring to early summer: noon temperatures are now up past 20°C, and migratory birds like the cuckoo and the pied flycatcher have arrived from their wintering areas in central Africa to our small cabin in the woods. Tonight I plan to finish my spring project of Classic Rich Field Galaxy Observation by completing my sweep of the supergalactic equator along ~12h30m R.A.

    
     I have in this project been zooming out, from the close by Local Supercluster groups (M81, CVn and M83, plus the M101 and Leo spurs), to the more distant Virgo Supercluster groups (Coma-Virgo and UMa). The galaxies I will be hunting down tonight are the most distant in the Virgo Supercluster, namely the Ursa Major Galaxy Group located at ~70 Mly, with the northern part of the group (> +50° DEC) that includes the Messier galaxies M108 and M109. These galaxies are faint and not well suited for wide field viewing, plus there’s a bad moon on the rise towards the SE (85% illuminated at 8° Alt. in Serpens Cauda). Combine that with a high humidity leading to sky glow (89%, SQM 18.0 ~ NELM 5.0), --  and I see trouble on my way….  “You gotta know when to fold’em”, but it’s not quite time to walk away, yet. You never count your galaxies, when you’re sitting at the table; there’ll be time enough for counting, when viewing is done. So up goes my Vixen FL-80S/640mm with Zeiss Amici revolver onto the saddle of the Zeiss 1b mount, and off we ride to distant Ursa Major, starting from Merak (Beta UMa).

        

Uma GG.jpg
*click*

    
     Using my Masuyama 2” 32mm eyepiece (34x @ 2½° FOV), I now place Merak outside the field towards the NW, and get a triangle of ~7m stars in the SE part of the field (btw. M97 the “Owl” PN is also in the field, just to the E of the baseline of this triangle, but I won’t pursue this target tonight).  Between Merak and the triangle is a small lambda-shaped asterism, with the tip pointing east to the position of M108. This edge-on SB-galaxy is not seen in my 10x56 bino, nor in my C60/250mm (6.3x) finder;  I use the 32mm Masuyama EP to plot the 2½° star field, but even  at 34x magnification I’m not able to spot M108. To detect the galaxy I have to click up to 44x (CZJ O-25mm), and I can then just suspect the faint fuzzy using a combination of averted vision and persistence, The observation is confirmed at 68x (CZJ O-16mm). This closely mirrors a previous observation I made 2 years ago with the 80mm Vixen refractor (2016-04-04, SQM 17.7/NELM 4.9). In both cases M108 was detected at 68x with AV, as a very faint featureless streak of light, though 2 years ago I was also able to identify a NE-SW elongation plus a slight increase in brightness towards the center.

    
     After a small break and a cup o’ tea, I now proceed to M109. Starting from Phecda (Gamma UMa), I pan the telescope a good ½° SE, where I find a line of three ~9m stars, with a pair of 9m stars another ½° further out to the E; M109 is located just NE of the middle star in the 3-star chain. Like M108, I’m not able to see this galaxy at low magnifications tonight (10x56 bino, 6.3x60mm finder), but I can just glimpse it with AV when pushing the magnification up to 108x (CZJ O-10). On a previous comparable observation 2 years ago, the M109 face-on SB-galaxy was seen from 30x magnification and up. See:  https://www.cloudyni...sier/?p=7570831.

    

    

UMa M108-M109 BLACK-S.jpg

*click*

    

Allan


Edited by AllanDystrup, 05 May 2018 - 06:50 AM.


#216 AllanDystrup

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Posted 05 May 2018 - 06:14 AM

.

Epilogue.

 

         

     Thus ends my little spring project of wide-field galaxy viewing with small refractors. I feel I’ve established a good understanding of the distance scale as well as the 3-D galaxy distribution, ranging from our local group to the Local supercluster and further out to the distant Virgo supercluster, all as seen in projection along the “Spring Milky Way of Galaxies at 12h30m R.A. in our earth-bound celestial coordinate system (which defines the Equator of the Supergalactic coordinate system).

 

 

     I’ll close with a summary of the galaxy distances and densities in the form of a few overview maps (see below).

 

     A tale of Three Superclusters...

 

     The Local and Virgo Superclusters both line up together on the northern hemisphere in the sheet of the ”Spring Milky Way of Galaxies”, roughly along 12h30m R.A. in projection on the celestial dome, with the Local SC in the foreground, and the Virgo SC in the background. The Fornax SC  is found on the southern hemisphere, roughly along 03h30m R.A. in projection, and it consists of the Fornax Cluster (65 Mly, incl. N1316 and 1365) plus the Eridanus Cluster (85 Mly, with N subgroup around N1407 and S subgroup around N1395). The Fornax cluster is below -35° DEC on our night sky, and thus impossible for me to observe from 56°N here in Denmark; The Eridanus cluster is better placed, with the N part (around N1407) at ~-20° DEC, and the S part (around N1395)  at -23° DEC. I’ll give the Eridanus galaxy cluster a try next winter!

 

 TTGG.png
*click*

 

     Below are shown maps of the polar regions in the Milky Way galactic coordinate system. On the maps are drawn galaxy number density contours (# galaxies/sqr. degree), calculated from the brightest galaxies as shown in the Becvár Atlas of the Heavens. From these galaxy density countours, I’ve outlined the major galaxy groups within 100 Mly, and marked how these come together in the three close by galaxy superclusters:  (1:red)  our own Local Supercluster at 20-30 Mly, (2:blue) the Virgo Supercluster at 60 Mly, plus (3:green) the Fornax Supercluster at ~75 Mly.

 

 

Spring GG Milky Way.jpg

*click*

    

    

    

     The next step up the distance ladder would take us from our own Hydra-Centaurus galaxy filament (including the Local and Virgo Superclusters <100 Mly away), out to the realm of really large scale galaxy structures at <500 Mly distance, such as other Supercluster filaments (Perseus-Pisces, Pavo-Indus), walls (Great Wall, Southern Wall) and voids (Local, Sculptor, Hercules). These are truly “Rich Field” objects spanning several constellations as seen from Earth, and well worth trying to wrap your head around, -- but for now I’ll put my galaxy hopping on pause.

     

    

Galaxy Mega Structures.jpg
*click*

 

    

     Maybe catch up again next spring smile.gif

 
Allan


Edited by AllanDystrup, 05 May 2018 - 06:53 AM.

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#217 Organic Astrochemist

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Posted 05 May 2018 - 09:14 PM

Great posts Allan.
I have enjoyed your tour through the spring galaxies.

One question to ask is why have you been able to see some galaxies and not others? The simple answer is that galaxies can be easily seen in small telescopes either because they are close and/or because they are bright.

Consider your observations of M108 and M109. I don’t know your source for the distance of this galaxy but newer measurements put it much closer ~10 Mpc (33 Mly).

http://leda.univ-lyo...=a007&o=NGC3556
If it was much further it would be hard to see because it’s not very bright, abs mag -19.93. Why is it not so bright? Because there aren’t enough galaxies around to build up a really big bright galaxy. The Kourkchi-Tully catalog suggests that M108 is in a galaxy group with only one member and a galaxy association with only about 6 galaxies — very low density.

We see M109 in spite of its distance because it is bright: abs mag -22.33. Why is it bright? Because there are lots of galaxies around to build up a great big bright monster galaxy: Kourkchi-Tully suggest that M109 is the brightest in a group of 24 galaxies and part of a galaxy association with hundreds of galaxies.

Edited by Organic Astrochemist, 05 May 2018 - 09:16 PM.


#218 AllanDystrup

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Posted 07 May 2018 - 03:51 AM

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Thanks, Organic Astrochemist -- always informative and thought provoking comments! waytogo.gif 

 

     Indeed, compared to the Virgo and Fornax galaxy clusters, the distant UMa cluster is poorly defined with no concentration toward a center, and located behind the superclusters (Local, Coma-Virgo) in the dense plane of the supergalactic equator.  Some consider it just a filament of the Coma-Virgo supercluster, while Tully concludes that the “spatial and velocity window isolates a sample of high-probability cluster members”.

    

UMa Group.jpg
*click*
     

 

     M109 (N3992, Vel.D. 479 km/s) is thus a member of the UMa group as delineated by Tully, while M108 (N3556, Vel.D. 700 km/s) is an isolated galaxy probably more related to the Virgo cluster (?). It is interesting also that the UMa cluster contains few E/S0 galaxies, while these are abundant in the Virgo cluster. I'm wondering what causes are at the root of this difference in galaxy types, -- probably it's related to galaxy age and proximity to a supercluster mass center.

 

     Both M109 and M108 show up as faint galaxies that are difficult to observe visually with small instruments. More photons (acquired by larger aperture or a ccd in front of the retina) will remedy this. Here’s a close-up drawing I made using live video yesterday, on 2018-05-06, 01:00 local DST (UT+2); Appologies for the quality -- I'm out in our cabin at the moment, chopping wood with the cuckoo, but without access to a scanner... 

 

M109-M108-DRAW2.jpg
*click*

 

 

 Allan  axe.gif 


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#219 Organic Astrochemist

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Posted 07 May 2018 - 09:46 PM

Nice sketches.

Thanks for the Tully reference on the Ursa Major Cluster of Galaxies. It's something I know nothing about and now want to investigate.

 

With respect to the number of elliptical galaxies in clusters, this type of galaxy is made by mergers -- galaxies need to come together to make elliptical galaxies. Virgo and Fornax both have higher masses and smaller radius (more important because of the third power) so they have much higher densities than Ursa Major -- easier for things to collide. Consider the crossing times: in Ursa Major, given the age of the universe, on average, a galaxy has crossed the cluster only twice (only two chances to hit something along it's path through the sparse cluster); in contrast, galaxies in Virgo and Fornax have crossed, on average over 12 times through the denser cluster -- more chance of collisions to produce elliptical galaxies.

 

With respect to observing galaxies I think that you are right that, just like for the pros, cameras (and Night Vision) are revolutionizing (and democratizing) the amateur experience. In the past, many galaxies, galaxy groups and galaxy clusters were beyond the reach of many amateurs due to bright skies and/or small telescopes. From my light polluted backyard, with my little lens (~65 mm aperture, ~50 - 100 mm focal length) I have been able to target and observe hundreds of galaxies this season. If I can stack images, anybody can. Of course, darker skies would reveal fainter objects and larger scopes would show much greater detail due to image scale, but the choice is no longer between observing and not observing (even under the moon).

 

Last night, between taking spectra of R Leonis and S Virginis, I was looking at the Coma Cluster, Abell 1656.

Here's an annotated image (the nearly endless PGC galaxies are not marked).

Abell 1656 annotated.jpg

and here's a link to the image.

Abell 1656

Personally, I am much less interested in how an object was observed rather than what object and/or details were observed. Others may have a different opinion. Observing every night with the same equipment helps form an understanding of the position in the sky, the apparent size and brightness of objects. This can then be complemented by distance data from the literature.

 

I'd be interested to see what you can make out of Abell 1367 or Abell 1656 with your R2. I bet you can see lots of Virgo elliptical galaxies.



#220 AllanDystrup

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Posted 08 May 2018 - 06:12 AM

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Organic Astrochemist,

 

     Very interesting what you describe for the predominant galaxy types we can observe in superclusters as a function of cluster mass/density and galaxy age/crossing times! It could be interesting in computer simulations to "wind back the clock" from the given current data, in order to observe how the clusters have evolved (condensed and aggregated) out of the primordial hydrogen clouds. We'll get there, eventually. 

 

     I'm perfectly aligned with you in respect to observing preferences; I observe from a ~5m suburban backyard on the outskirts of Copenhagen with small refractors, but clicking in a small cheap R2 ccd "eyepiece" in my turret, I can suddenly observe and draw details that can only be seen with muggler glass eyepieces using a ~12" telescope from a dark site. With the R2 I do "instant" live video on a small lcd screen, typically with 2½s exposure, 36 dB gain and optionally a running average of 1-5 frames (no stacking). To me there's no difference in that experience under the night sky as compared to observing with glass eyepieces, -- apart from the explosion in detail that can be pulled out from the same instrument.

 

 

Personally, I am much less interested in how an object was observed rather than what object and/or details were observed.

Others may have a different opinion.

      Amen! to that, couldn't have said it better myself.  waytogo.gif

 

 

     Now you caught my interest with the Coma (Abell 1656) and Leo (Abell 1367) superclusters! I plan on having a look at these clusters in the center of the "Great Wall" tonight grin.gif

 

Allan



#221 AllanDystrup

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Posted 22 July 2018 - 03:38 AM

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The Milky Way star clouds and H-II regions.

    
        
     The star clouds in the arms of our Milky Way galaxy contain a multitude of young OB-associations as well as older open clusters, all born from dense nebulae of neutral Hydrogen gas (H-I) in the galactic disc. The massive hot type-O and early B stars in the young stellar associations emit high energy UV-radiation that excites the electrons in the interstellar medium (ionized Hydrogen: H-II), which then emit photons at the red wavelength of 656nm (Hα spectral line) when the hydrogen atoms jump back to their lower energy state. The Milky Way arms are rich in such star birth areas with Hα emission nebulae (H-II regions), as is evident when looking at Hα images of our galaxy.

 

         

     In previous posts of this rich field thread I have described some of the major OB-associations in our Milky Way galaxy, and also briefly touched upon a few of the emissions nebulae connected with the associations, -- but my main focus till now has been on stellar astronomy, for the primary reason  that my observing conditions (suburban backyard) and tools (80mm refractor, glass eyepieces, R2 live video cam) simply have not allowed a detailed study of delicate wide field nebula structures.

 

     I do own a “classic” 1950’ies US army gen-0 night vision device (sensitivity ~60 µA/Lm) and also a 1960’ies single stage gen-1 Russian civilian NV monocular (200  µA/Lm), but these are not well suited for astronomy for different reasons. This has changed however, as I have recently acquired a modern gen-2+ military NV monocular (>700 µA/Lm) that does allow me to study the H-II regions in our Milky Way in rich detail. This, I hope, will open a new portal to the Milky Way ISM (interstellar medium) structures, which I look much forward to explore and share with you.

 

     For an overview, I’ve created an annotated map of the Milky Way (in galactic coordinates, from ‘Galaxy Map’). The solar system position is on the inner edge of our Orion-Cygnus spiral arm, so when we look south from mid-northern latitudes, this is what we see:

 

Milky Way Ha - S.jpg
*click*

    

  •      In Summer we face towards the galactic center (gal. long. 0°), where we see part of the Central Bulge at 30 Kly distance as the Great Sagittarius Star Cloud, and part of the innermost incurving Norma Spiral Arm at 15 Kly as the Small Sagittarius Star Cloud (M24). Most of the open clusters and nebulae in this direction (Lagoon-Trifid-Swan-Eagle) are however located at only ~6 Kly in the nearest inner spiral arm from our solar system: the Sagittarius-Carina arm. The Sco-Cen OB association is an even closer (0.5 Kly) Gould Belt feature of the inner edge of our own Orion-Cygnus spiral arm.
         In Scutum we are beginning to look lengthwise down the Sag-Car arm (the Scutum Star Cloud), while in Cygnus we are looking at the incurving arc in the rotational direction of our own Ori-Cyg arm (Cygnus Star Cloud). Finally in Aquila (between VUL and SER) we are facing the interarm gap between the two Ori-Cyg and the Sco-Cen galactic spiral arms.

        
  •      In Winter we face in the direction of the galactic anticenter (gal. long. 180°), and thus we look into the core of our own Ori-Cyg spiral arm at relatively nearby (2-3 Kly) open clusters, associations and nebulae in the Gould Belt: from Perseus (α Per OB) to Taurus (Pleiades, Hyades) and Orion. Further south opens a view along the length of our trailing Ori-Cyg arm at still more distant open clusters and nebulae: from Auriga – Gemini (4-5 Kly) to Monoceros – Canis Major (5 up to 20 Kly at the Galaxy’s far outer edge).

    

-- Allan


Edited by AllanDystrup, 22 July 2018 - 04:51 AM.

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#222 AllanDystrup

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Posted 22 July 2018 - 09:34 AM

.

The Cygnus OB associations revisited.

    

    

     I’ve previously observed the major OB-associations in The Swan (see my:-> Cygnus Wide Field sub-project <-in this thread), where I also described the Cygnus Super Bubble (CSB) structure of emissions nebulae:

 

OB144x, 136x NGC 6888 WR136 w. Crescent Nebula   
       6x, 136x NGC6960/6992 Cygnus Loop SNR ~ Veil Nebulae
 
OB7 34x       NGC 7000 North America – IC5067/70 Pelican Nebulae
 
OB9 34x       Gamma Cygni/Sadr region with IC1318b-c Butterfly Nebula
     136x       IC1318a Nebula

    

     These observations were done in visible light with traditional glass eyepieces (wide field 6° - 2° FOV) supplemented by close-up live video (½° FOV); My modern NVD however offers an extremely wide field of view (from 40°/1x to 13°/3x) in combination with a tremendous boost in light gain, which allows the use of very narrowband Hα (656nm) filters.  A narrow bandpass such as a 6nm FWHM Hα (although still 100x wider than a 0.06nm solar Hα etalon) increases nebula contrast by completely suppressing skyglow and artificial light, and it thereby makes emission nebula observation feasible even from my NELM ~5m suburban backyard. Let’s see where this can take me.

    

    
     It’s an early morning in late July (2018-07-21, 01:30 local DST, CEST UT+2). Both transparency and seeing are above medium, and the LP is Bortle orange (NELM: 5.6m at zenith), which is quite respectable given my 56N latitude bright suburban backyard, now deep in Nordic astronomical twilight around midnight.

      My first target for the emission nebula project is Cygnus, which is close to 90° Galactic Longitude. In this constellation we are looking lengthwise in the direction of rotation down the incurving arc of our own Orion-Cygnus Spiral Arm. The closest stars in the arm show up as the Cygnus Star Cloud, with the dust clouds on the inner edge of our Orion-Cygnus Arm forming the Great Rift. Further down in Aquila we look towards the relatively empty interarm gap between our own spiral arm and the next inner Sagittarius–Carina Arm; The latter can be followed from Scutum and further south, winding around the Galactic Center in Sagittarius.
 

MW-Gygnus-S.jpg
 

    

     I start with the NVD at 1x with a LP-filter, which opens a ~40° field encompassing the constellations Cygnus, Lyra and Sagitta. The Cygnus Star Cloud is spectacular, contrasted by the relatively star poor surroundings, from the Northern Coal Sack between Deneb and Sadr, to the Great Rift curving SE of the Cygnus Cloud down to Sagitta and beyond. Stars to 7m are easily seen, which means that I can identify all the Cygnus OB-Associations in one field of view. Nice!

     Resolution from 8m and fainter starts to get difficult though, so it’s harder to identify open clusters, -- I can detect NGC6871, NGC6888, NGC6910 and M29 which I consider not bad for a 1x mag view, but I expect to get better at adjusting focus, sensitivity etc. on the device, allowing me to go deeper with some practice.

 

 

Cyg-01-A-Ann-S.jpg
    

Cyg-01-B-Ann-S.jpg

    
 

-- Allan


Edited by AllanDystrup, 22 July 2018 - 09:52 AM.

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#223 AllanDystrup

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Posted 22 July 2018 - 11:21 AM

.

The Cygnus OB associations and H-II regions.

    

    

     Changing now to the 6nm Hα filter, the H-II emission regions show up strong in Cygnus:

  • Sh2-117   in the southern part of the OB7 region, including the NAN, Pelican and IC5060 illuminated parts of the Hydrogen cloud
     
  • Sh2-109   in the Cygnus Star Cloud, with the Butterfly nebulae (IC1318 in OB9 and OB8) around Gamma Cyg, plus the smaller Propeller (OB8), Crescent (OB1) and Tulip (OB3) nebula “knots”all embedded in the large swirls of nebulosity from Sigma Cyg past Sadr to Eta Cyg.

 

     On close inspection I’m also able to glimpse the eastern and western parts of the Veil SNR (Sh2-103).
     Not bad for 1x viewing from a Bortle Orange suburban backyard... wink.gif

 

 

.Cyg-02-B-Ann-S.jpg

 

Cyg-02-B-Ann-S.jpg

 

-- Allan


Edited by AllanDystrup, 22 July 2018 - 11:28 AM.

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#224 GlennLeDrew

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Posted 22 July 2018 - 11:52 AM

Allan,

You'll doubtless have discovered the great reduction in effectiveness of the narrowband H-alpha filter at larger off-axis angles, due to de-tuning. Which is why the 3X lens will be better to use--if your filter is large enough.

 

If you aim nearer to the North America, you'll readily see Sh2-119 not far away to the east. This elliptical shell is illuminated by the runaway O star, 68 Cyg, traveling southward away from its parent association in Cep (unknown by me with certainty which one--possibly Cep OB2.)


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#225 moshen

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Posted 23 July 2018 - 03:20 AM

     I do own a “classic” 1950’ies US army gen-0 night vision device (sensitivity ~60 µA/Lm) and also a 1960’ies single stage gen-1 Russian civilian NV monocular (200  µA/Lm), but these are not well suited for astronomy for different reasons. This has changed however, as I have recently acquired a modern gen-2+ military NV monocular (>700 µA/Lm) that does allow me to study the H-II regions in our Milky Way in rich detail. This, I hope, will open a new portal to the Milky Way ISM (interstellar medium) structures, which I look much forward to explore and share with you.

 

Allan, congrats on the Night Vision Device. Your detailed, well researched and expertly presented observing reports combined with annotated iPhone snaps is going to make for some very interesting and educational reports. I'm really looking forward to this!

 

In a similar way that listing your refractor & aperture gives equipment context to the readers of the observations can you let us know a bit more of your NVD? Based on your location and the fact that it's a white phosphor tube I'm guessing it's a Photonis Intens 4G?

 

EDIT: I see you have this listed in the lower left image description box. Nevermind!


Edited by moshen, 23 July 2018 - 05:30 AM.

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