[sac-forum] Last Chance for M101/M102 review

For June we're going to divert from the normal constellation selection and follow a different path.  For this we will study the only outstanding unsolved mystery of the Messier Catalog and that is, is M102 a duplicate observation of M101 or not, and if not, what are the likely candidates?  The short story is there isn't enough information to make a correct decision; at least not with the information available.  Our assignment is to go out and observed M101 and a number of other galaxies that are thought to be M102 and report your results.  To start with we must observe M101, a magnificent face on spiral galaxy, which Méchain described as,

101. 13h 43m 28s (208d 52' 42") +55d 24' 25"

(March 27, 1781) `Nebula without star, very obscure & pretty large, of 6 or 7 minutes [of arc] in diameter, between the left hand of Boötes & the tail of the great Bear [Ursa Major]. It is difficult to distinguish when one lits the [graticule] wires.' (diam. 7')

For the observation of M102, wherever it is, Méchain described M102 as,

 (Méchain) `Nebula between the stars Omicron of Boötes & Iota of the Dragon [Draco]: it is very faint; near it is a star of the sixth magnitude.'

(Handwritten position added by Messier in his personal copy: 14h 40m, +56.)

In all of your observations, look for the 6^th magnitude star.  Where is it?  Remember, though, this is a visual observing estimating the magnitude of a star.  Could it be off by a magnitude or so?

So much for the introduction now let’s move on to the objects for us to study.  We start with the obvious M101.  The NGC candidates are a selection of the brighter galaxies in the area.  The first galaxy takes us into Boötes, is mag 12.5 NGC5899.  Magnitude 12.8, NGC5908 follows.  The third is magnitude 11.1 NGC5907 a late type spiral.  Second to last NGC5879 another spiral galaxy at magnitude 12.2.  Finally, the last is a popular pick for M102, is magnitude 10.8 NGC5866, an early spiral.  Some of the above galaxies have other field galaxies included.  Just for the observational fun of it, let us know which ones you can identify.

Include your opinion of which object you believe is M102 and don’t let the popular pick sway your selection.

For July let’s try Ophiuchus – again.  It has lots of nice globular clusters, so let’s look for some new stuff.  While doing the globular clusters do some comparison of size, brightness and resolvability.  First is M12, located almost 3° west of 12 Ophiuchi; about half way there you’ll pass a nice three star arrangement of 8^th mag stars.  Be sure to notice it in your finder if you use the star hop method.  Next is IC4665, a large bright naked eye open cluster a little more than one-degree north east of 3rd magnitude Cebalrai (beta Ophiuchi).  Count the stars and estimate their brightness.  We now start on a southerly tour of the constellation, beginning with M62, which is just across the border from Scorpius.  There isn’t any short hop from a bright star, so start with epsilon Scorpio and swing almost 5° north of northeast and you will easily sweep it up on your finder.  On to M19, which should be an easy slew north for about 4°.  Again, it should be visible in your finder.  Next is NGC6316, which is just across the other side of the Pipe Nebula’s end, otherwise it is 1.5° south of 36 Ophiuchi.  Can you see the Pipe Nebula naked eye?  Yes or no.  Finishing off our southerly tour is NGC6366, which is 1° west of 4.5 magnitudes SAO141665.  We now finish up with NGC6633 way out on the western side near Serpens.  This open cluster is a switch from globular clusters and we don’t have any naked eye star to hop from, so use your binoculars and locate 5.7 magnitudes SAO123516 that is within a degree of the cluster.

Now, because the summer monsoon is such a drag on our observing schedule, here’s the constellation and objects for August.  It is the desert denizen found as part of the SAC logo, Scorpius.  I’m not sure why this one has been skipped for so long, perhaps due to its southerly declination?  No more!  Let’s see what it has to offer.  Naturally we will start with, and do all of the Messier entries, beginning with M80 located 1.5° northwest from omicron Scorpii.  If you star hop this one, take a gander at the Milky Way you traverse between the two.  Next is easily located M4, in the same finder view of Antares and 1.3° to the west.  Both of these globular clusters are easily seen in modest size finders.  Next is a planetary nebula, NGC6153, and is quite a hop from our last object.  So get ready for some fun here, it is 6.3° east of southeast from 3^rd magnitude eta Lupi and is not visible in moderate sized finders.  Now, going back to clusters find the magnificent NGC6231!  It is a naked eye galactic cluster located about ½ degree north of zeta Scorpii.  Can you detect the cluster without any optical aid?  If you have binoculars available, or can borrow a pair please do, give this area a nice once over, you will be most happy to have done so.  Moving on, towards the tail, find M6, about 5° north of northeast from Shaula, or lambda Scorpii.  Finally, there’s M7, a scant 3.8° southeast from M6.  Both of these clusters are so large and bright you should be able to see them without any optical aid.  Can you see them this way?