Observing Report – 12/06/2000

Melotte 25

Melotte 25 [credit: NASA/ESA/STScI]

Wide-field observations of Open Star Clusters.


Telescope:  Takahashi FCT-76
Location:  Cedar Park, Texas, USA
Time:  1 am – 3 am
Seeing:  5-8
Sky Transparency:  9
Limiting Magnitude:  ~ 5
Lunar Phase:  Waxing Gibbous


On nights when the sky transparency and limiting magnitude are high, I like to do one type of observing: Wide-field.   Tonight was beautifully clear – allowing my small scope to go “deeper” than would normally be possible in my suburban skies.


  • Cepheus Stellar Association – [that’s what I call it] In the center of Cepheus is a large grouping of 5th and 6th magnitude stars almost 5° wide which looks great at 16x with the Tak.  If you have a wide-field scope or appropriate finderscope, take a look.
  • Melotte 20 – Alpha Persei Moving Group.  This large 5°+  star field just fits in the 31mm Nagler, where both Alpha and Delta can be seen at the fov edges.  The main grouping looks like a paper hat made of stars within which there is a prominent yellow star I believe to be Sigma.  Streamers of stars flow southward and lead to 2 stellar multi-colored triangles.
  • M 45 – The Pleiades Cluster.  Very few telescopes show the Pleiades well because of its large size, but with the FCT-76 I can see all of the cluster plus the outward radiating stars.  One of the main reasons for owning a rich-field telescope is to provide perspective; that is, to show the totality of an object within the context of its surroundings. When seen this way, it looks like a beautiful blue-white stellar cup placed underneath a fountain of field stars pouring into it from directly above.
  • Melotte 25 – The Hyades Cluster.  I can almost get the whole cluster in the eyepiece [a Tak FS-60C would do better with its 6.7° fov].  Aldebaran looks very yellow and many colorful stars cross the V-shaped pattern [mostly yellows and whites].
  • Collinder 70 – Orion Belt Stars.  This grouping looks ice cold due to the prolific blue-white stars here. There is a clear deliniation of stars directly above the belt which highlights the amount of dust in this region.  Below the belt, I see one distinct pale-orange star.  A line from Sigma [an amazing multiple star system] through Zeta points the way to M78, which looks like a faint round glow. Moving from Delta to Orion’s sheild, there are many field stars that flow like an arching river upward.
  • M 41 – As many times as I’ve been wowed by it, I still find it hard to understand why the astronomy periodicals don’t lavish more attention on this cluster.  M 41 is large and has many bright colorful stars and multiples.  One of the nicest views of the cluster involves positioning it in the same fov with the nearby star triangle of 15, 17, and 19 Canis Majoris [which all appear yellowish to me], and helps to project a 3D-like contrast between the two.  Just below 17 CMa are 2 white stars that form a mini-triangle of their own with the brighter primary – very nice.
  • NGC 2362 & H 3945 – Another lovely contrasting duo are the open star cluster NGC 2632 and the double star H 3945.  NGC 2632 is small, compact, and centered on Tau CMa.  Most of its faint stars look white to me.  H 3945 is a great double star of large separation consisting of yellow and blue-white members very reminiscent of Beta Cygnus.
  • M 46/47 – This is my favorite “double cluster” in the sky [actually it’s a “triple cluster” if you include the fainter NGC 2423 just above M 47].  Of the three clusters, M 47 is the easiest to view with my small 3″ refractor.  A large cluster, it contains many bright white stars and an obvious double in the center.  M 46 is much harder to spot in light polluted skies but was much easier tonight and appears as a spherical glow [I could resolve around 20 stars vs. dozens and dozens out in West Texas].  NGC 2423 is hardly a smudge in suburbia and so didn’t make much of an impression tonight.
  • M 93  – This is a small cluster that shows well in a rich Milky Way star-field.  Most of the 30 stars visible look bluish-white and form a stellar “X” pattern right down the center.  I found it curious that the cluster looked brighter to me at 16x than at 29x [don’t know what was going on there].  I could see the stars with less strain at low power rather than high.  Even though I have a hard time observing this cluster from home, I always take a peak at it.
  • M 44 – The Beehive Cluster.  Nestled inside the star triangle of Delta, Gamma, and Eta Cancri, is the large open star cluster M 44.  Overall, the cluster is spread out with several colors of stars visible along with doubles and multiples towards the interior [at around 40x, many of these can be appreciated].

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