Being a deep-sky observer for whom most galaxies and nebulae are inaccessible, I am posting extracts from the logs of a recent observing session of mine for those of you, if anyone, who is as fond of viewing galactic clusters as I am. For others, this post will be much too long.
On Tuesday, April 11, I went stargazing at Cottonwood Springs, Joshua Tree National Park (California), with my 8-inch Celestron SCT. The seeing was substantially compromised by the light of the 12-day old moon, so that the glow of the milky way which is usually apparent to the naked eye at that 3,000-foot high location was completely washed out. However, the air was still and free of moisture, offering enough transparency for good views of the season's many open clusters, and I therefore restricted my viewing to those objects. Mostly I used a Parks Gold Series 20 mm eyepiece that I recently acquired for viewing clusters, and I occasionally switched to a Meade 24.5 mm SWA eyepiece for wider fields of view.
The season's prominent open clusters listed by Messier (M35, M36, M37, M38, M41 and M47) were all brilliant, as were the less prominent M46, M48 and M50. After admiring these and other old friends, I inspected the following clusters that I had not studied before:
NGC 1662 in Orion, seen at 102x, showed me about 12 stars within a diameter of about 15 arcminutes, of which 7 were fairly bright and the others rather dim. I likened the shape and orientation of this cluster to NGC 2244, the open cluster at the core of the Rosette Nebula. Archinal & Hynes says this cluster contains 59 stars within a diameter of 12 arcminutes, suggesting that I missed seeing a swarm of dimmer stars among the dozen I saw.
NGC 2194 in Orion looked like a small, dim swarm of numerous stars. This is consistent with Archinal & Hynes which states that this 8.5-magnitude cluster contains 194 stars within a diameter of 9 arcminutes. An old Lowell Observatory photo on page 1345 of volume 2 of Burnham's handbook shows the cluster as just barely distinguishable from the numerous field stars that surround it.
NGC 1778 in Auriga, viewed at 102x, appeared as a small open cluster in which an equal-magnitude double star is prominent. An observer of the Webb Society who viewed the cluster in a 10-inch scope also noted it as a "Small group containing several doubles including an equal 10 mag pair at the centre."
I noted NGC 2281 in Auriga as a "brilliant" open cluster, whose stars filled most of the 30-arcminute field of view of my eyepiece at 102x.
Viewing NGC 2251 in Monoceros at 102x, I saw 15 or more stars of various magnitudes stretched east-west across about 75% of my eyepiece's 30-arcminute field of view. This is consistent with the observations of the Webb Society's observer who described NGC 2251 as "25 stars in a streak; 20' x 5' diameter." On the other hand, Archinal & Hynes refers to this as a cluster of 92 stars within a diameter of only about 10 arcminutes.
Observing NGC 2324 in Monoceros at 83x, I first saw it as a Y-shaped group of several stars of approximately equal magnitudes, among some outlying star of different magnitudes. When I switched eyepieces to 102x, I saw a small dim swarm of stars around one of the brighter outliers. This swarm is apparently the true NGC 2324, as confirmed by the data in Archinal & Hynes and the Webb Society handbook.
NGC 2232 in Monoceros was too extensive for the 30-arcminute field of view of the 20 mm eyepiece. Seen at 83x in the 24.5 mm eyepiece, it was a fairly large scattering of stars, some of which were quite bright. This is consistent with the Webb Society observer's description of NGC 2232 as "15 stars in 20' x 10' field; bright," and with Archinal & Hynes' rating of it as a cluster of just 20 stars in a field whose diameter is 53 arcminutes, with a total visual magnitude of 4.2
NGC 2401 in Puppis showed me a very dim small swarm near two somewhat brighter stars. Had I mis-identified the cluster? Archinal & Hynes rates this as a 12.6-magnitude cluster of 20 stars within a 2-arcminute diameter field.