Monthly Summary 2 (mid-April/mid May 2013)

     The clear sky gods were not around much this past month, though now that the moon is waxing they seem more abundant.  I have had a disappointing spring session, though I've tried to make the most of the few decent nights we did experience.  Most disappointing has been my initial season observing all of the NGC objects in Leo, along with a healthy selection of double stars and such.  And once Leo was too far west, I had hoped to get a good start on Bootes.  Oh well, at least the planning is done and next year I should be able to start right back in again with Leo.  There is still a chance that I can score a few more galaxy hits there near the end of this month.

     Here are the details.  All 16 new NGC objects logged this past month were galaxies.  15 of them were in Leo, and 1 was in Bootes.  A few were large and spectacular, some were reasonably bright and interesting, and several were so faint they could barely be seen with averted vision.  As it was last month, the highlight was the Leo Triplet, consisting of M 65, M 66, and eg 3628.  Last month I was able to sketch and log M 65, so this month M 66 and eg 3628 seem new, even though they have been observed many times before.  Until the sketch and notes of an object are entered into my observing logbook, I do not consider it as seen.  Two other galaxies within easy star hop of the triplet also provided highlights for the month.  Eg 3593 is large and bright, and lies within a notable star pattern, making it easy to find again once it has been located for the first time.  Eg 3596 is a bit north and considerably fainter, though also large.  The galaxy has become a marker for me for good seeing.  If this round object can be easily seen, then the hunt for much fainter galaxies is on.

     Another trio of galaxies provided me with a few nights of thrills.  This group marks my third triplet in Leo, even though I have barely begun my explorations there.  Egs 3607 and 3608 are a stunning and close pair, very bright and quite large in a 12".  Visually they are mag. 9.9 and 10.7, respectively.  3607 is considerably brighter, and has a bright inner core.  Its nearly circular shape is offset by a slightly oval 3608, an object that is also considerably smaller.  The third member is the smallest and faintest, but is fair game for an 8" mirror or higher.  Eg 3605 is just south preceding 3607, perhaps a bit more oval than 3608, though similar in shape.  An interesting group of faint stars is just south following eg 3607, including a close, faint double star.

eg 3605 is the smallest of these three galaxies in Leo.

eg 3607 is largest and brightest.  eg 3608 also fits

into my view at 150x.  South is at the top.

Image from http://www.astrosurf.com/benoit/ngc.html

     Most of the rest are very faint galaxies, showing little detail except perhaps shape.  These include the following:  egs 2913, 2919, 2923, 2928, 2933, 3805, 3592, and 3598.

     Only one galaxy was logged in Bootes.  Eg 5490 is visually mag. 12, with a much dimmer surface brightness due to its modest size (13.7 mag.).  I was pleased with finding this one from my back deck under a 6-day old moon.  I even saw an extremely faint 2nd galaxy directly north of it, though I cannot find a name for this object.  I had been searching for 5490C, but this was not it.  Nor was it "B".  Perhaps I shall call it 5490D.  Alas, what is life without little mysteries?

     Also this month I managed a few close looks at different parts of the lunar surface, as well as a few superb views of Saturn, mostly around midnight when the air had settled down.  I also viewed a whole slew of large, bright galaxies, double stars and the wonderful globular M3 as part of my scope's computer tours (see previous blog entry for details).

     In other news, the Astroscan 4" has been sent off to Edmund Scientific in NY.  Either they will be able to clean the mirror or they will replace it.  Deb and I look forward eagerly to its return, hopefully for the next dark moon phase.

Mapman Mike

The Leo Triplet of Galaxies

     There has not been a great sky for galaxies here since April 5th.  However, the upcoming early week forecast looks good.  There have been a few nights with lots of haze, including the last few nights.  Thursday was the full moon, and Deb and I went out on the deck to watch it rise.  We also brought out some binoculars, and made a good scan of the whole of Leo, something I had not yet done.  I usually focus on one small area at a time, and am prone to lose "the big picture" as a result. 

     On Friday night we had about 45 minutes of dark sky before moonrise.  We set up our 2nd scope, the 4 1/4" Edmund Astroscan rft.  Sadly the main mirror has deteriorated to the point where we will have to send it off to Edmund Scientific to be replaced.  They will put in a new mirror and collimate it for around $140.  We recently purchased a tripod for it, as well as a red dot finder-scope.  One of the first things we looked at on Friday was M44, the Beehive Cluster.  Too large to fit into the field of most telescopes, the Astroscan was made for just such a task.  With the 28 mm eyepiece giving 16x, the cluster was quite impressive even in twilight.  Next, we scooted around some of the brighter stars and doubles in Leo, easily splitting Gamma at 50x (18 mm eyepiece with 2x barlow).  Gamma is one of the finest doubles out there, mag. 2.6 and 3.8, separated by 4" of arc, with both stars appearing golden yellow.  In the 12" it looks like a pair of headlights approaching, but it is still lovely in the 4".

     Last night, with about 90 minutes of dark sky before moonrise, we set up both scopes.  The evening had plenty of hazy clouds.  They went away for awhile, but then returned.  Despite this I was able to officially log M66 and eg 3628.  I have observed the Leo Triplet nearly every clear night for the past month and a half, and I have yet to tire of any of the three objects.  Last night I was able to use 200x on M66 and M65, getting bright, crisp views whenever the haze would move on.  It was easy to hop back and forth, even at high power.  This remarkable pair of galaxies was not noticed by Messier when a comet passed through the field in 1773.  According to Mechain, who did log them, the comet was probably too bright.  Imagine a comet passing through this area that blotted out those two bright galaxies!

     Noting the differences between the two Messier objects makes for good observational training.  M65 is more elongated, not quite as bright, and has a barely visible (in the 12") dark lane down its east edge.  This is more an impression than an easily observable feature, but I have seen it more than once.  M66 is the brighter galaxy, slightly less elongated, and has a blazing core that lies not in the center, but just a bit to the north.  This galaxy will take any magnification and still appear bright.  They both fit into my 100x field, and I will continue returning to them throughout the season.

     NGC eg 3628 is probably, after M31, one of the largest galaxies I have ever seen.  It is viewed edge-on, and is extremely elongated.  Using averted vision and 100x or 120x, it just goes on and on and on.  Almost featureless in the 12", other than more brightening near the middle, it still makes a wonderful site.  The darker the sky, the better this one appears, but even through haze I was able to get decent views.  NB: In March 2014 I easily observed the dark lane running all across this galaxy.  It was a superior observing site and a very good sky.

     Two other smaller galaxies appear near the triplet, and one of them is very much worth seeking out.  Immediately preceding M65 and M66 are three brighter stars in a straight N/S line.  Star 73 is the one in the north, with two slightly fainter ones due south.  Eg 3593 immediately precedes the middle star, and should be easily visible in an 8" scope.  It is elongated E/W, and pops into view more readily than eg 3628.  It is about 1/3 the size of that galaxy, but is a very enjoyable sight in the 12", its bright core easily seen.  With averted vision and 100x, the full extant of the arms can be seen.  If I cannot see this galaxy on a given night, then I know the sky is a bad one.  Lately it is my first test for a quality galaxy sky. 

     A fifth galaxy is also nearby, and makes an excellent final test for good skies.  Eg 3596 is the faintest of the five, lying north of the three stars just used to find eg 3693.  It is south of Theta, also called star 70.  This, too, is a big galaxy, oval but much harder to see than the others.  If this one pops up right away at low power, I know I have an excellent night of galaxy hunting ahead.  Last night it only appeared as a threshold object at medium-high powers.

     I have yet to officially log these fourth and fifth galaxies, though I have sketched eg 3693.  They will both be logged on the next good night.  All five galaxies are an easy star hop from one another, and I now know my way around this area extremely well.  If you have not visited these galaxies yet, I can highly recommend them.  Telescopes of 8" or higher will offer rewarding views, especially if you go back often.  In the 12", even from suburban skies, they are quite stunning and unforgettable.

Mapman Mike

#15: Full Moon: Dark Skies Just Ahead

     The time just before and after full moon is perfect for tweaking one's observing plans.  Spring constellations are available to us for such a short period of time compared to summer, autumn and winter ones that careful preparation is even more important than usual.  I have been trying to make a decent start on Leo, and beginning two nights after full moon I hope to resume my work.  Immediate observing projects are to observe and sketch M 66 and eg 3628.  As the moonrise is gradually set back far enough in the evening, I will leave my back deck and set up my scope farther afield in dark sky locations.  I don't know yet whether I'll be able to observe in the 'preceding' area of Leo, where I have a whole collection of faint objects remaining to see, or if I will have to immediately move my observing session more towards the middle and 'following' sections of Leo.  Leo begins at about 9h 22m r.a., and continues until 11h 58m r.a.  No doubt I will still get lots done in Leo if it's clear, but not necessarily from the first pages of my object list, which generally follows r.a. of the constellation I am observing.

     One thing is for certain; Leo will set relatively early during the night.  Though I have notes prepared for Lyra, I decided I needed something to bridge the gap between Leo and Lyra.  Bootes seems to fit the bill nicely, though I have already observed it in some detail with the 8" scope.  Bootes begins at 13h 16m r.a., continuing to 15h 12m r.a.  Bootes is a galaxy-filled constellation of difficult NGC objects, and it contains not a single Messier object or galaxy of real brightness.  Besides galaxies, there is a lone, very faint globular cluster.  Having already viewed and sketched the brightest galaxies and the cluster, there may be little remaining for me to see except the dozens of much fainter galaxies.  While I don't mind reviewing previous brighter galaxies in the newer 12", I also want to add new NGC objects to my life list.  The good news is that right about now where I live, the trees usually begin to leaf.  When this happens, a lot of ground light pollution is blocked and the sky grows a bit darker.  Any slight advantage might make the difference between seeing a faint galaxy or not seeing it.  This year in southern Canada, however, we seem considerably behind in seasonal changes, and I may have to wait one more full moon before the trees are of much help.

     Leo also offers two close-up charts in Uranometria.  Charts A10 and A11 are galaxy-filled playgrounds, and I hope to make a good start on Abell 1367 (Chart A11).  I haven't yet decided on an observing strategy for this remarkable area.  I will first determine which objects and how many are actually available to me by having a quick look there.  If many or most of them are visible, then I will likely enjoy a galaxy-filled observing orgy over several nights.  As I enjoy star hopping so much, I'm certain to love galaxy hopping, too!  If my skies do a poor job of allowing me decent access, then I will likely plan a road trip with my telescope for next spring to somewhere very dark in order to experience this feast properly.  In fact, an upcoming post will likely be about dark site road trips.  Where to go, when to go, why to go and which way to go.  So stay tuned.

     Full moon is also a perfect time to tune up the scope and accessories.  Cleaning eyepieces and the finder-scope is a great idea, and perhaps doing some collimating on the secondary and primary mirrors isn't such a bad idea, either.  And of course it is a perfect time to scour the web and catch up on some blog reading!  Until next time enjoy the full moon, and join me in anticipating the dark-sky nights that will come soon afterwards.

Mapman Mike

#12: Visual Magnitude versus Surface Brightness

     Any discussion about observing galaxies must inevitably come round to the subject of the galaxy's brightness or lack of it in the eyepiece.  Galaxies that I could barely see in my previous 8" scope are now much easier to locate, identify and discuss using my 12" mirror.  However, an entire new spectrum of much fainter galaxies is now available, going well beyond what the 8" might have seen.  If I suddenly started using a 16" scope, then the faintest ones now seen with the 12" would appear brighter, and a whole slew of new and fainter galaxies would be available to challenge my view.  This process would literally go on and on with each larger mirror.  There is no end to the faintness of distant galaxies, as evidenced by Hubble's deep field explorations.

     I am still trying to determine the faintest galaxy that I can view in my nearby dark sky with the 12" scope.  So far it has to be NGC 2873 in Leo, with a visual magnitude of 15.4 and a surface brightness of mag. 13.6.  While there are several fine explanations on the web as to exactly what visual mag. is, and surface brightness, I will give my own version here without equations, based on my current understanding and experience.

     Visual magnitude refers to how much actual light is coming from the galaxy to the observer's eye.  How it reaches the eye is greatly affected by the object's size.  Some bright galaxies (Messier 66, for example) have a bright visual magnitude, making them seem relatively easy to see in a wide range of small telescopes.  The visual mag. for M 66 is given as 8.9.  If that object was a star, it would be considered somewhat faint but still easily observable in a small telescope.  NGC 2873, by comparison, has a visual mag. of 15.4, making it nearly impossible to see if it was a star, except with a moderately large scope.  If 2873 was as large an object in the eyepiece as M66, it would never be seen in amateur scopes.  And yet the surface brightness levels of the two galaxies are not that far apart.  For M66 it is given as mag. 12.7, and for 2873 it is mag. 13.6.  There is less than a magnitude difference between these two vastly differing objects!  And yet in fact there is more than six magnitudes of difference between them in actual visual light.  A difference of one magnitude is 2 1/2 times, with mag. 10 being 2 1/2 times fainter than mag. 9, for example.  This is most interesting.

     The size of a galaxy, then, is important in determining its brightness, and in making it easier for the eye to see it.  Without getting mathematical (not my strength), let us take 3 hypothetical galaxies as our examples.  Our first galaxy is going to be sized at 1'.1 x 1'.0 (arc minutes).  This is a somewhat small object, and virtually round.  If the visual mag, was, say, 13 (from all the light coming from it), then the surface brightness would be the same mag. as the visual one.  That exact size of object has the same visual mag. as its surface brightness. 

     However, if we now expand the galaxy to 2'.2 x 2'.0, then the surface brightness decreases (there is an easy formula for this).  The same amount of visual light is now spread over an area 4x as large.  A galaxy of mag 13 might now become one with a surface brightness of 14.7 (not an exact answer, just an example, but it will be 4x fainter). 

     If we now shrink the galaxy to something like 0'.55 x 0'.5, then the same amount of light now arrives in a more compact, star-like package.  The surface brightness now increases, so that our imaginary galaxy with a visual mag. of 13 now seems more like a 12 mag. galaxy (again, just a rough answer--the formula is available on-line if you want exact answers).

     The upshot of all this is that a large galaxy that looks bright on paper might actually be very hard to see at the eyepiece, because its light is spread out over a large area (NGC 45 in Cetus is a good example--that one also has a bright star attached that interferes with seeing the fainter haze of the galaxy)).  And a tiny galaxy like 2873  might seem at first to be impossible to see, but is actually a bit easier because of its very small size (its actual size is 0'.8 x 0'.2).  Which magnitude is the one that observers should pay attention to, visual or surface brightness?

     In my experience, neither one should be used apart from the other.  Even taken together, there are still so many other factors to consider when hunting galaxies.  Some of these factors include how high above the horizon it lies, if it is near a bright star, the transparency of the sky and overall seeing conditions, and even how tired you are.  And if the galaxy is the same brightness as the sky background, it will be invisible.  When galaxies get too far west I stop observing them, as that area of sky is very light polluted.  I take both figures with me outside on the clipboard, along with the size.  If the galaxy is very large and bright, then the surface brightness formula only works to a certain degree.  A combination of the two magnitudes is often a better way to go.  M66 lists a visual mag. of 8.9 and a surface brightness of mag. 12.7.  You can't see a 12.7 mag. galaxy in a 4" telescope, but you can see M66.  Halfway between 8.9 and 12.7 is magnitude 10.8, which seems closer to the truth in this case.  A 4" scope can now work very hard and show the galaxy pretty well on a decent night.  My 'split the difference' method is unscientific, but seems to work for me in the field.

M66--is it really only 0.9 magnitude brighter than

 NGC 2873?  M66's vast dimensions (9'.1 x 4'.1) make

its bright magnitude appear dimmer to the eye.

Both photos from

http://www.astrosurf.com/benoit/ngc.html

NGC 2872 on right.  NGC 2874 on left.  Both are easy

to locate in a 12" scope.  Much trickier is tiny NGC 2873,

lying just north of the two larger Leo galaxies,

 in the upper center of the photograph.  The photos

show true relative size of all galaxies depicted, including M 66, above. 

     The same goes for NGC 2873.  I could never hope to see a galaxy of 15.4 magnitude in my skies with a 12" scope, and the galaxy certainly doesn't reach its given surface brightness mag of 13.6 either.  Halfway between the two figures lies mag. 14.5, which gives a more reasonable ballpark estimate as to what my observing companion and I observed a few nights back.

     So for now, I am assuming that I can see a tiny mag. 14.5 galaxy in a good sky with my scope.  This will aid me in knowing which faint galaxies to attempt and which ones to pass up.
Of course the companion volume to Uranometria 2000 is also an awesome source of this information.

As ever, I am curious to hear what you think.
Mapman Mike