An Open Cluster in Gemini
Gemini is one of the constellations I always turn my telescope to. There’s a deep sky object for every size telescope to see. Like the open cluster M35. I’m not sure of the exact date but M 35 was observed and cataloged between 1756 and 1746 by Philippe Loys de Chéseaux. Charles Messier cataloged it on August 30, 1764 and acknowledges that John Bevis’ had made an independent discovery of this cluster brfore 1750 as it appears in his Uranographia Britannica which was completed in 1750.
M35 (NGC 2168) consists of several hundred faint stars over an area as wide as the full moon. M35 is 2,800 light years from earth and shines at magnitude 5.3. Under dark skies, the naked eye finds this cluster easily near the three foot stars of Gemini. Small telescopes will resolve the brighter stars and make a pleasing view at low magnifications. The cluster appears nearly circular and uniform in low power eyepieces.
This cluster is of intermediate age, and contains some post-main sequence stars, including several yellow and orange giants of spectral type late G to early K. Its hottest main sequence star is spectral class B3. If you have a larger telescope you may be able to see open cluster NGC 2158 situated just about 15 arc minutes southwest of M35. Because of its compact size, NGC 2158 was once taken for a globular cluster candidate.
Tweet this!The Alpha Persei Cluster
Perseus is still in good position in early February, high in the North-West around 9:00 PM EST for Northern mid-latitude observers.
Perseus is still in good position in early February, high in the North-West around 9:00 PM EST for Northern mid-latitude observers. Perseus holds a few open clusters for owners of small telescopes such as M34, NGC 1245 and of course the Double Cluster (NGC 884 and NGC 869). But I want to turn your attention to a cluster that is mostly ignored by backyard astronomers, partly because it doesn’t appear on many sky atlases and it is rarely mentioned in articles. That object is known as The Alpha Persei Cluster, also cataloged as Collinder 39 and Melotte 20. The Alpha Persei cluster takes its name from the constellation’s brightest star, Alpha Persei (Mirfak) which is a member of the cluster. The cluster is about 50 million years old -just one percent of the age of the Sun and lies some 600 light-years away in the rich star fields along our galactic plane.
Many astronomers refer to this cluster as an association because it is loosely bound by gravity. This loose type of open cluster is also
called an OB-Association since the clustered stars are mainly of the young, massive, and hot spectral types O and B. These associations are quite unstable and have short lifetimes before they evaporate into space. The cluster is not rapidly dispersing but its members are moving in the same direction.
The Alpha Persei Cluster is easy to locate simply by looking at Mirfak (Alpha Perseus) in the constellation Perseus. To the naked eye, the cluster consists of several stars of spectral type B, along with the most massive member — the F5 supergiant Alpha Persei. The brightest members of this cluster include Alpha, Delta, Epsilon, Psi, 29, 30, 34 and 48 Persei. Binoculars or a rich-field telescope give the best view of the Alpha Persei cluster. Keep the magnification under 20x and even at such low power, you’ll see about 50 bright stars from a dark sky site, and somewhat less under light polluted skies. All told, more than 100 young stars brighter than magnitude 12 spread across the association’s 3° width.
I have provided a finder chart showing the Alpha Persei Cluster just in case your atlas doesn’t show the cluster. You can download it here.
Until next time, clear skies!
Tweet this!All this for $25 bucks
January 2 I got out with my latest addition to my telescope collection, a Celestron 60mm refractor I picked up from a flea market vendor for $25 bucks. The scope was in poor shape, dusty, dirty optics, the mount falling apart, all the earmarks of a telescope someone didn’t understand. So I fixed it up and all is well.
So the first observing session of the New Year with a new (new to me) telescope was underway. For first light I choose M35, an open cluster in Gemini. I used my 25mm Plossl, you know the one that Celestron supplies with most of their telescopes, which gave me 36x. I stuck with this eyepiece throughout the night. M35 filled the field of view with about 50 stars. The most noticeable thing is the contrast. The sky is dark in this telescope due to the long focal length.
Next up is M38 in the constellation Auriga. At magnitude 7.4 I knew this cluster would present an interesting view. The familiar “Pi” shape was evident with this telescope and I could count about 30 pin points of light. The open cluster NGC 1907 nearby was visible as a smudge of light with averted vision at the edge of the field of view.
Located north-east of the star Betelgeuse in the constellation of Orion is the star cluster Collinder 69 (Cr 69). The Collinder objects are mostly neglected by backyard astronomers with small telescopes because they are large with little or no concentration toward the center giving them a very sparse appearance. It’s definitely worth a look as this cluster includes the double star named Meissa. It is a striking view in the 60mm at 38x, not rich in stars but there are six bright stars that stand out from the field.
Since I’m hanging around this area of the sky I may as well have a look at M42. I guess you knew that was coming. The sky contrast makes the brighter areas of M42 stand out well. At 38x I can split the Trapezium (theta Orionis) with ease and the surrounding nebula is all aglow, albeit somewhat featureless. M42 is still an impressive view however but then, M42 is impressive in 10×50 binoculars, making it one of the true showpieces of the winter sky.
I guess my $25 bucks was well spent. I got a Celestron 60mm refractor that may have sold for around $100 to $150 new. It didn’t come with any eyepieces or dust covers but once everything was cleaned up the scope performed as well as I expected it to.
Tweet this!Total Eclipse
This was an event worth missing sleep for. It was cold and windy but I didn’t seem to mind. I took a few photos which I still need to process but I do have one for you to look at in the gallery…http://www.90mm.us/gallery/moon-images/.
Tweet this!Charioteer’s Treasures
Auriga's deep sky targets in this article
November didn’t offer many opportunties for me to get out and observe but, I did get out early in the month to have a closer look at some well known Messier’s and NGC objects. This observing run centered around RA 5h 10′ and 5h 40′ and DEC +31° and +37°, so it just a small block on your star chart.
There’s a small grouping of stars just visible to the naked eye that some refer to as the “Leaping Minnow”, as though it was “leaping “out of some celestial waters into the night sky. You should be able to spot this asterism a few degrees Northwest of Elnath (beta Auriga). Through binoculars and small telescopes this group forms a parallelogram (sort of). The brightest star here is 16 AUR which is a spectroscopic binary. I see the star as yellow which agrees with its spectral class of K2. The full spectral class of K2 5IIIb indicates that 16 AUR is a giant star. What color do you see? Star colors can be affected by sky conditions where you are observing from, degree above horizon as well as visual accuracy of the observer.
Just about a degree northeast of 16 AUR is the Flaming Star Nebula (IC 405). I was unable to detect this nebula with my 150mm refractor regardless of magnification used. Since my location suffers from moderate light pollution, a nebula filter may have helped but I didn’t have one handy. Owners of larger telescopes may be able to pick this object out under light polluted skies and certainly small telescopes under a dark sky will show this object. IC 405 lies about 1500 light years distant, and spans about 5 light years across. Going back to 16 AUR and moving your telescope about 5’ west, you’ll locate the open cluster NGC 1893. This much overlook cluster is embedded in the nebula IC 410. With my 150mm refractor I can clearly see the cluster but the nebula requires at least a 12-inch telescope and dark skies. I count about 17 stars around 10th magnitude. About 2.25° Northeast of NGC 1893 is open cluster M38. This is one of those two-for-one objects. With a low power (38x) eyepiece I can see both M38 and open cluster NGC 1907 in the same field of view. NGC 1907 appears as a smudge of light flanked to the north by two 10th or 11th magnitude stars. M38 at 54x in my 150mm refractor shows about 25 stars around 10th magnitude and I can just start to detect a few fainter stars with averted vision. Pumping up the power to 88x, M38 fills the field of view and many more stars become visible. NGC 1907 at 54x starts to show some granulation with averted vision, hinting that this object is an open cluster. At 88x the nature of NGC 1907 becomes apparent. I can start to resolve 11th magnitude stars. Look for the bright nebula NGC 1931 a little more that a degree south-southeast of NGC 1907. At 54x in my 150mm refractor this object is faint and rather featureless and requires averted vision to see well. I increased to power to 88x and the nebula was easier to see. The nebula appears somewhat irregular in shape with 10th or 11th magnitude star on the edge. My last target for this session is the open cluster M36. M36 presents a much tighter grouping of stars than M38. At 38x I count 15 stars somewhat condensed toward the center and, at 54x many more stars are resolved. I can’t help but to notice the chains of stars flowing outward from the clusters center.
All of the objects mentioned here can be found in Sky & Telescope’s Pocket Sky Atlas
Until next time, clear skies,
Dan
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