Object of the Week, December 4, 2022: Messier 103

Messier 103 (NGC 581, OCL 326)
Open Cluster in Cassiopeia
RA: 01h 33.4min
Dec: +60° 40min
Mag: 7.4vmag
Size: 6'

Moon is rising, so for everyone still out there I will present one of the more easy objects in the sky - the open cluster Messier 103.

Discovered by Pierre Méchain in 1781, Messier add the cluster in his catalogue in 1783 without observing the cluster by himself. An interesting fact is, that M 103 was the last entry in Messier's original list. The first detailed description came from William Herschel who spoke from about 14-16 "large" stars. Admiral William Smyth was the first who described the red giant star near the middle of the cluster.

Astrophysical there is nothing spectacular about M 103. With its distance of around 7160 Ly (WEBDA) it has the same distance than the famous double cluster h & ? Persei. It belongs to the Cas OB8 association, together with its neighbours NGC 654 or NGC 663. Modern studies listed 172 members. The brightest star HD 9311 (Struve 131) at the NW tip is a multiple system (A/B 13.8"). The second brightest "star" is a red giant near the middle. It is in discussion whether both stars belongs to the cluster. Only the brighter star HD 9365 at the SE tip does not belong to the cluster. With its young age of around 25 million years it mostly consists of several type B blue super giants of around 10-11mag.

Someone may ask if the OOTW of the deepskyforum.com is the right place for a bright open cluster. In my mind yes, because its is simply a beauty in nearly all optics, no matter if 1000mm is your aperture or your focal length. But what makes the cluster so observable nice. First of all its unusual shape of a triangle with a red star in the middle. With 6' diameter the triangle becomes visible in a 10x50 binocular, while the red colour of its giant in the middle starts to shine from around 8-inch, maybe smaller? But there is more. Alan MacRobert calls M 103 in his nice book "Star-Hopping for Backyard Astronomers" the "M 103 family of clusters" and he is right. With a field of 3° we can find several bright clusters, like NGC 654, NGC 659 or the larger NGC 663. Taking a telescope, Trumpler 1 is another highlight only 0,7° NE. More challenging is IC 166 NE of NGC 663. Star charts also shows a "PK" object only 23' W of M 103. Sadly it is no Planetary Nebula but an "Emission Line Star". I add two sketches below. Sketching open clusters is not always possible, but for M 103 the opposite is true. For nearly all apertures it is a funny project to sketch the object, to see as many stars as possible and to manage to show the shape which delight us.

photograph: 12", LRGB, Bernhard Hubl
Attachment 4948
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sketch: 20x125 binocular, NELM 6m3
Attachment 4949
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sketch: 27", 4129x, NELM 6m5+, Seeing III
Attachment 4950
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Now it is your turn - GIVE IT A GO AND LET US KNOW

An unorthodox choice for an OOTW, Uwe, but I learned something new from your post — that this cluster is physically related to the rich NGC 663 nearby, amongst other such clusters.

I decided to post my first observation of this object, because about 2 weeks ago, I got back my first ever observing logbook that was at a friend's place for nearly a decade. The observation was made on 16th September 2005 in Bangalore, India with my 8" f/8 telescope. I wrote of the sky conditions, "Terrible sky; 14th day moon; thin haze". Of the object itself, 17-year old me was not at all charitable:

"A not impressive cluster in Cassiopeia. Has only 4 bright stars and some other faint stars. Not very impressive, at least tonight."

This is the accompanying sketch:
Attachment 4951
(I flipped the orientation of the Y-shaped pattern on the right)

Clearly, my opinion of the object from a truly darker sky is better, which I have had a few chances to see. But placing it in the physical context of other Cassiopeia open clusters makes it much more interesting.

Hi, here's my observation from 1/4/2008 : Messier 103 open cluster in Cassiopeia ; magnitude: 7.4 ; size: 6' ; wide range in brightness ; wedge shaped ; moderately compressed ; I used a 14mm Meade Ultra wide eyepiece at 153x with my 14.5 Starstructure f/4.3Attachment 4952

Great choice for an object of the week, a bit different from usual but I like it because it's one of the fewer objects in this forum that I actually observed :)

I observed and sketched this one with my 10" under a mediocre sky, but even then M103 appears as a beautiful OC. The cluster is strongly defined and contrasts beautifully with the sparser field around it. The brightest star has a definite orange/yellow hue and together with other members of the cluster, it resembles the point of an arrow. On the N side (down in my sketch) double star STF 131 can be seen.

Attachment 4953

Like Akarsh, I will take a trip down memory lane.

This beauty in Cassiopeia was in fact the very first object for which I ever logged an observation! It wasn't much, a 5" Mak under Moonlit skies in October 2003, with me attempting to make a start at a methodical approach to stargazing. This is what I noted:

The shape of the cluster is recognizable from images, although only the brighter stars are visible.

There. With that my observing log was born.

Fast forward to present day... night. Since 2003 I have 4 entries in my log for this cluster. Most recently in my latest observing run, 19-20 November 2022. An hour-long session from my backyard, tackling STF double stars in the Queen. With STF131, I also logged the cluster. 14" SCT @ 178x / 27':

Observed simultaneously with the double star STF131 that is on the NW edge of the cluster.

The cluster is quite detached but not very concentrated, consist of mainly mag. 10.5 and fainter stars. East of the middle is a notable mag. 8 star (component A of the double star BUP22). Centrally the cluster is more concentrated in a rectangular / square part with the orange mag. 8 star on the eastern edge. From the central part two notable branches are visible, towards the west and the SW.

Rated it 7/10.

Attachment 4954 Attachment 4955

Here is the guide for this week's object.

For me it was one of the last Messiers to see in my 15 cm telescope. My notes from 2007 (more than 15 years after having started observing with that telescope!) read:

Visible as a line in the finder. NGC 663 lies close by because of which this cluster doesn't stand out much. At 146x I see a triangle of stars with a bright star as the northern tip, a bright star at the southeastern tip and a faint star at the southwestern tip. Within these three stars lie about all stars of the cluster. I count about 20 in total. Someone compared it to Patrick Star from Spongebob Squarepants and I can see why.

:D

It's one of the showpieces of the heavens, for sure.
From my log:
med.size, triangular shape, very brite, in a large field of many clusters, fully resolved, brite stars at the triangle's corners, slight concentration@ one corner, red star near center.
Fairly rich in stars, well detached, almost no central concentration. Difficult to tell if many of the faint stars seen are actual cluster members.