#13: More About Galaxies

     I said awhile back that 5 of every 6 non-stellar objects plotted in Uranometria 2000 are galaxies.  That only includes objects to 15th mag.  If we dip down to 17th or 18th mag, virtually every object past 15 is a galaxy.  They are difficult to avoid if observing faint objects.  Since this blog is currently concerned with the NGC catalogue (and much of the IC list), I will only discuss the main list at this time.  With over 7800 objects of all types in the NGC list, galaxies still reign numerically supreme.  It might be of interest to look at which constellations have the most NGC objects within their boundaries, and just what type those objects are.  Because I live and mostly observe at latitude 42 degrees north, I will only discuss those constellations which are visible from mid-northern latitudes.

     The constellation (north or south) with the most NGC objects is........Virgo!  Not a huge surprise to seasoned observers, I'm sure.  Virgo has 637 NGC objects.  And guess what?  636 of them are galaxies!  There is one lone globular cluster (gc 5634).

     Number two on the list with the most NGC objects is....Ursa Major.  There are 407 NGC objects.  Only two are non-galaxies!  There is a single very famous planetary nebula and one open cluster.

     Number three constellation is Cetus.  Some of it is a bit low in the sky for me, but it is all there.  Cetus has 383 objects.  There is one lonely and very low surface brightness planetary nebula (NGC 246).  The rest are galaxies.

     Number four on the list and close behind is Leo, with 378 NGC objects.   Every single one is a galaxy!  No relief here, though it is peppered with some lovely double stars and multiples.  I am currently beginning my extensive and hopefully exhaustive exploration of this early spring constellation.  It will take me many years.  To date, I have located 13 of its NGC galaxies, though I've officially logged only 9 so far (it`s been pretty cloudy).

     Number five is Eridanus, a constellation that winds from north to south, meaning that I cannot see all of it from my latitude.  With 315 NGC objects, it has one reflection nebula and one planetary nebula.  All the rest are galaxies.

     So, then, the top five constellations for northern latitude viewers contain a total of 2,120 NGC objects.  That`s about 2/7ths of the entire list.  And a whopping 6 of those objects are non-galaxies!  Let`s continue through the top ten NGC constellations.

Number six is Pegasus.  With 298 NGC objects, only 3 are non-galaxies.

Number seven is Coma Berenices.  293 objects.  It has 3 globulars.

Number eight is Draco.  287 objects.  2 planetary nebula.

Number nine is Pisces.  270 objects.  All galaxies.

Number ten is Bootes.  267 objects.  1 globular.

     We are now up to 3,535 objects, nearly half of the NGC list!  All are galaxies except for 15 objects!  I don't know about you folks, but I find this quite astonishing and somewhat amusing.  "Well," you say, "what about those rich milky way summer constellations?"  OK.  Let's look at Scorpius.  Lots of interesting objects there.  Scorpius has a grand total of 71 NGC objects.  There are some totally amazing ones, too.  However, there just isn't a whole lot of them compared to those galaxy constellations (Sagittarius has 77 NGC objects).

     After the top ten NGC constellations comes Hydra, Canes Venatici, Hercules, Andromeda, Aquarius, Cancer and Lynx.  All are very heavy with galaxies.  I am not trying to prove any point here, but merely stating some interesting (for me) facts.  And no, I did not count the objects myself from the atlas.  This website does it for me.  
http://www.nightskyatlas.com/constellations.jsp

I did, however, scan through each constellation's list to search for non-galaxies, so there is some original research involved.

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Here are a couple of older sketches each depicting a galaxy I saw with my previous scope, the amazing Edmund 8":

My first attempt to scan some early sketches.

eg 4565, Coma Berenices.  112x.

15'.8 x 2'.1  Vis. Mag. 9.5.  Sur. Br. 13.2.

One of the showpieces of the heavens.

eg 4448, Coma Berenices.  72x.

3'.9 x 1'.4  Vis. Mag. 11.2.  Sur. Br. 12.9

The star field is at least as interesting

as the galaxy.  The scale for this sketch

is obviously not the same as for the one

above--I cropped this one a lot.

Happy galaxy hunting!

 

Mapman Mike





#9 NGC Life List

     In my very first post earlier this month I talked about astronomers who work their way methodically through object lists, often to the detriment of the object.  A quick glance, a note or two, maybe a quick sketch and then they are off to the next object.  All well and fine if you are looking at 14th magnitude galaxies, but if your list is packed with the brightest deep sky gems, what is the hurry?  400 top objects could well last your entire life.

     To make certain that I never finish my life list, or run out of options on any given clear night, I chose the NGC list a long time ago as my main deep sky emphasis.  I will not pass a Collinder or Berkeley cluster without a look, but my longest viewing time is spent on the NGC list.  In a lifetime of observing I have only seen about 630 of them, averaging just over one per observing session (last night I logged two new ones).  I really need to ramp that up a wee bit if I want to see all available from my latitude before I die.

     The new edition of Uranometria 2000 claims that more than 30,000 non-stellar objects are on its charts.  That's over 22,000 more than are in the NGC list.  Good grief.  Makes me kind of thankful that I am not overly obsessed.  Of those 30,000 objects, nearly 26,000 of them are galaxies.  Which means that nearly 5 in 6 non-stellar objects viewable in the night sky with amateur scopes are galaxies.  Most of those are pretty faint, too.  Here is the breakdown, as reported on the atlas' back cover:

     25,883 galaxies

     671 galaxy clusters (Abell)

     14 star clouds

     1,613 open clusters, including those in the Magellanic Clouds

     170 globular clusters

     355 bright nebulae

     367 dark nebulae

     1,145 planetary nebulae

     260 radio sources

     35 x-ray sources

     I remember being very surprised when I first learned how many galaxies were available to amateur astronomers (all the ones listed in Uranometria are mag. 15 or brighter).  I mean that I was very surprised.  Growing up loving the Milky Way area and all of its clusters and nebulae, it was easy to conclude that clusters of stars far outnumber galaxies.  That, to say the least, was an erroneous conclusion.  If one decides to choose the NGC for a life list, one must be prepared to see some galaxies.  I don't just mean the ones in the Messier catalogue, either.

     Finding and doing justice to galaxies requires the very finest of dark skies.  I used to be able to pick off 12th mag. galaxies from my back deck with my 8" scope.  Light pollution has increased so much in my area that this is now quite impossible.  I did snag one last night with the 12", but if I want to do a decent job of observing in Leo this spring, I have to be prepared to travel with the scope.  This brings on an interesting conundrum.  I also had a preliminary look last night at M 65 and M 66, bright galaxies in Leo.  Compared to faint little eg 2894 viewed previously, they were pretty darn impressive.  So, do I observe the brighter galaxies from my home, saving the fainter ones for country skies?  Though this is a feasible plan, I try to imagine what eg 2894 might look like from a dark sky.  If I can even see it from home, then it might just be that much more impressive from a dark sky.  Should I save all my faint objects for darker skies?  What about M 65 and M 66?    Of the two, M 65 was less bright but it was really huge after viewing it for a few moments.  M 66 was quite bright, and I could probably have used up to 300x without any loss of brightness.  However, what would these objects look like from a really dark sky site?

     One solution to this problem, which I'm certain many of us face all too often, is to keep notes and report on the brighter ones as seen from home suburban skies, but also return to them in dark skies and enjoy a quick peek.  eg 2894 seemed to have a little cluster of very faint stars superimposed over it, only barely resolvable at high power with averted vision.  Was there a stellar core?  Couldn't really tell.  But the elongated galaxy could be seen in behind the star field, best at 150x in the 12".  I know I want another look in darker skies, resolving those faint stars more easily and perhaps seeing some detail in the galaxy itself.

    Whereas fainter galaxies pose severe problems for suburban viewers, objects such as clusters and nebulae, especially planetary (I also enjoyed good views of pn 2346 in Monoceros last night), do not pose significant problems.  And double star work can carry on quite well, too, often even during full moon nights.  However, I am determined to do as much deep sky work in the darkest skies I can reach.  I've been spoiled by my northern Ontario early years of observing.  Another time I will talk about my nearby observing options, and how they may best be used.  Until then, I hope you enjoy a clear sky night or two.

Mapman Mike