I enjoyed two clear nights at Zephyr Ridge Observatory (ZRO) on April 21-22, and in this post I will discuss my observations.
I recently purchased a Unihedron Sky Quality Meter (http://unihedron.com/projects/darksky/), a device that measures sky brightness. I measured the sky brightness at ZRO several times during each night, and intend to continue taking and tracking these measurements.
For those who are unfamiliar with the idea of measuring sky brightness, I suggest reading this excellent article by Brian Skiff: http://www.astropix.com/HTML/L_STORY/SKYBRITE.HTM According to Mr. Skiff, a sky that is completely free of man-made light pollution would obtain a sky brightness reading of 22 mag/arcsec2. He also suggests that a “true-dark” site is one that achieves a reading of 21.5 mag/arcsec2 or higher.
On April 21, I visually judged the sky to be decent, but perhaps a notch below the best I have experienced at ZRO. The average meter reading I recorded that night was 21.40 mag/arcsec2. This is the average of nine measurements taken over the course of the night, all taken with the meter pointed to the zenith. I excluded three readings taken just after the 77% gibbous moon had risen; these readings averaged 20.78 at zenith, showing the deleterious effect the moon has on the sky even when at the horizon.
On the next night the sky looked better visually, and I judged it to be on par with the better nights I have experienced at ZRO. I was pleased that meter agreed with my assessment, this time achieving an average of 21.53 mag/arcsec2. I will continue to report my experiences with this device in future posts.
On to my observations! The majority of my observations were of galaxies and galaxy clusters. With my 20” Obsession, I am able to enjoy the varieties of shapes and features that are often invisible in smaller instruments, and I endeavor to carefully record these nuances. I provide a list below, but would like to call attention to some notable objects.
First, I recommend NGC4038/4039 in Corvus, the so-called Antennae Galaxies. These galaxies should be visible in smaller instruments, and it is well worth the effort. This is an impressive interacting pair of galaxies, although I did not actually see the long filaments that account for the name.
Another bipolar gem is the Planetary Nebula NGC2371 (or NGC2372) in Gemini, also bright and suitable for smaller instruments. I had observed this before, but not at ZRO, and so treated myself to another view of this fine object. Catch it while you can, as Gemini is receding in the western sky. By the way, NGC4361 in Corvus is another excellent Planetary Nebula.
Lastly, I successfully observed the Proto-Planetary Nebula known as Frosty Leo. Here is a link to a nice article about such objects: http://www.schoenball.de/astronomie/projekte/ppn/ppn_en.htm Frosty Leo is considered a challenging visual object, but with my 20” Obsession and dark sky I was able to see it without difficulty.
I would be interested to hear from readers about your experiences with these or other objects in the April (and May) sky. April is “galaxy month” in the northern hemisphere, as there are many fine galaxies in prime position. I hope you have seen or will see some of these distant “island universes.”
Denis
4/21/11 10:15 PM
NGC2371/2372 Planetary Nebula Gem Mag 13
RA 07h25m35s Dec +29°29’36” Size 1.23’x0.9’
Calming wind and clear, but some moisture content in the air reduced my transparency rating one point below “perfect.” At 363x this PN is clearly bipolar. The SW lobe seemed to have a condensed core region – like the core of a galaxy – and this made it a little brighter than the NE lobe, which appeared more diffuse. In between the lobes I could see the central star. Averted vision revealed it, and once I was able to see it with direct vision after spotting it with averted vision. There is a smattering of stars nearby. An apparent double star appears on the north side of the nebula. Very nice object.
4/21/11 10:25 PM
NGC2811 Galaxy Hya Mag 11.3
RA 09h16m11s Dec -16°18’47” Size 2.7’x1’
Possible partial obstruction with wall on SW corner. At 212x this galaxy appeared to be an oblique or edge-on spiral. It is fairly small and has a bright and tightly condensed nonstellar core that yields abruptly to a diffuse elongated halo. There is a bright star just to the west of the core. There is a faint star – seen more easily with averted vision but sometimes also directly – just off the halo on the NE side of the galaxy.
4/21/11 10:33 PM
NGC3962 Galaxy Crt Mag 10.6
RA 11h54m40s Dec -13°58’31” Size 2.9’x2.6’
At 212x this is a small, fairly bright fuzzy. It has a bright nonstellar core, and direct vision showed a rather small halo. With averted vision, the extent of the halo was much greater, although the glow was rather subtle. The halo was slightly elongated. There is an arc of 4 stars that places a bound on the south side of the galaxy; the two western stars of the arc are bright and the two eastern stars are fainter.
4/21/11 10:48 PM
NGC4027 Galaxy Crv Mag 11.1
RA 11h59m31s Dec -19°15’59” Size 3’x2.3’
At 212x this is a large and diffuse galaxy, with a roughly circular halo that gradually brightened towards the center. The halo is rather large, and there is a faint field star overlapping the halo on the east side, and another faint star just off the halo to the west. A bright pair of stars appeared to the north. I did not see the companion NGC4027A.
4/21/11 10:55 PM
NGC4038/4039 Galaxies Crv Mag 10.7
RA 12h01m53s Dec -18°51’54” Size 3.4’x2’
Very interesting. At 212x this quite clearly looked like two interacting galaxies. The initial impression is of a V-shaped region of nebulosity, or, put another way, two intersecting lobes separated by a dark area in between, with the intersection occurring at the ends of the lobes at an angle. The two lobes seemed to be elongated and mottled with no obvious central brightening. The northernmost lobe, NGC4038, is shorter and wider, and the stellar material seemed denser. The southernmost galaxy, NGC4039, is longer and thinner. With averted vision I could pick up stellar pinpoints towards the center of each lobe. There is a star just off the halo of NGC4038 to the north. I did not see the antennae protrusions visible in photographs.
4/21/11 11:08 PM
NGC4361 Planetary Nebula Crv Mag 10.9
RA 12h24m31s Dec -18°47’05” Size 1.9’
Quite nice. At 212x this appeared as a moderate-sized gray disk, roughly circular with a mottled appearance. The central star is obvious. Using an OIII filter, the blotchy/mottled appearance was accentuated and the object now seemed a little elongated. One of the better PNs.
4/21/11 11:31 PM
IRAS 09371+1212 Frosty Leo Planetary Nebula Leo Mag 10.5
RA 09h39m54s Dec +11°59’00” Size 12″
At 212x this nebula was easy to spot just to the east of a field star, and I confirmed the location with a map. It was a faint, small glow visible with direct vision. At 363x I was able to see a slight bit of elongation, but the wind had picked up during this observation and the seeing may have degraded, as I preferred the view at 212x. Central star was not visible. I did not see lobes or other structure; perhaps on a better night? Inserting an OIII did not help; in fact, I was unable to see anything at all.
4/21/11 11:44 PM
NGC2654 Galaxy UMa Mag 11.8
RA 08h49m12s Dec +60°13’14” Size 4.3’
At 363x, a nice elongated streak. Clearly an edge-on spiral. Fairly large, with a bright elongated core. I could glimpse a stellar pinpoint nucleus with averted vision. The extended halo was fairly bright and easy to see. There are nearby field stars, most of which were near the SSE side of the galaxy.
4/21/11 11:55 PM
NGC2681 Galaxy UMa Mag 10.3
RA 08h53m33s Dec+51°18’49” Size 3.8’
At 363x this galaxy is quite bright, with a bright, small core and stellar nucleus. The halo is roughly circular and offers a fainter contrast to the bright core. There is a very bright star to the SE of the galaxy, just outside the field of view. Within the field, there is a pair of bright stars roughly west of the galaxy, with another bright star north of the pair. Approximately east of the galaxy there is a wider pair of bright stars.
4/22/11 12:04 AM
NGC2787 Galaxy UMa Mag 10.8
RA 09h19m19s Dec +69°12’11” Size 3.4’
At 363x this galaxy is fairly bright, with a large, elongated core and an elongated halo. I noticed a possible field star within the halo, and another star just off the halo to the SE. Also, there were two field stars roughly west of the halo and another to the NW.
4/22/11 12:17 AM
NGC2841 Galaxy UMa Mag 9.3
RA 09h22m03s Dec +50°58’35” Size 8.1’
A fine object. At 363x it appears as an oblique spiral, with a large bright core. The halo is also large, and on the NE side of the galaxy the halo seemed a little pinched in as compared to the SW side of the galaxy, and so I suspect a possible dust lane on the NE side. (There is also a bright star off the NE side of the galaxy.) There are bright stars towards the NW tip of the galaxy – three bright ones and one fainter one – and one of these four stars appears contained with the halo.
4/22/11 12:28 AM
NGC2859 Galaxy LMi Mag 10.7
RA 09h24m19s Dec +34°30’49” Size 4.8’x4.2’
At 363x this galaxy has a bright nonstellar core with an approximately circular halo. On first impression the halo seemed small, but with patience and averted vision I could see more extension. Photos show an inner halo and a separate outer ring; I did not see this separation, but I speculate that perhaps with averted vision I was picking up some of this outer ring. My map showed a superimposed field star on the northern side of the halo, but I did not see it. There is a bright field star off the WNW side of the galaxy.
4/22/11 12:38 AM
NGC4179 Galaxy Vir Mag 10.9
RA 12h12m52s Dec +01°18’01” Size 4.2’x1.2’
At 363x this galaxy was a nice elongated streak. The core was bright and had a stellar nucleus. The halo was rather small. There is a field star on the NW tip that is clearly embedded within the halo. There are also field stars NE of the center of the galaxy – a pair of faint ones close in and a wider pair of brighter stars further out on this side.
4/22/11 12:46 AM
NGC4273 (and others) Galaxy Vir Mag 11.9
RA 12h19m56s Dec +05°20’38” 2.3’x1.5’
This galaxy is located in a nice field of several other galaxies, and I used a map to navigate among these. At 363x, NGC4273 appeared fairly large with a somewhat elongated halo with only slight brightening towards the center. I saw a stellar pinpoint near the center; whether this was the nucleus or a field star is uncertain. Just off the halo to the east I saw a faint smudge that is just north of a field star, which I identified as NGC4277. Returning to NGC4273 and moving SSW, I saw NGC4268, which was easy to see, with a bright core and elongated halo. There is a nearby field star to the NW of this galaxy. Returning to NGC4273 and slewing roughly ENE, I found NGC4281, which was bright with an elongated core, stellar nucleus and elongated halo – looked like an edge-on spiral. Returning to NGC4273 and slewing north from there, I found NGC4270, which appeared as another elongated halo with a slightly brighter core and stellar nucleus. Moving further north there are a pair of very bright stars, and just south of the westernmost member of this pair I was able to pick up (with averted vision) a very faint elongated fuzzy, which I identified at NGC4266. There are even more galaxies I could have hunted in this field, but I decided to stop here.
4/22/11 12:59 AM
NGC4527 Galaxy Vir Mag 10.4
RA 12h34m09s Dec +02°39’11” Size 6.3’x2.3’
The moon has now risen in the eastern sky. At 363x this galaxy is elongated and has a brighter core area and with averted vision I glimpsed a stellar nucleus. The halo had a filmy appearance that gradually diffused into the background. There is a field star roughly west of the galaxy.
4/22/11 1:04 AM
NGC4536 Galaxy Vir Mag 10.4
RA 12h34m27s Dec +02°11’15” Size 7.4’x3.5’
I confirmed the location of this galaxy with a map. At 363x this galaxy appeared as a large hazy glow – rather faint – with no real brightening towards the core. I did see a stellar nucleus.
Next night:
4/22/11 9:52 PM
NGC2373/2375/2379 Galaxy Cluster Gem Mag 14
RA 07h26m37s Dec +33°49’26”
Very good conditions this evening. Excellent transparency and good seeing. At 363x, these galaxies do not quite fit into the field of view. The smallest of the group is NGC2373, which appeared as a tiny fuzzy spot just to the SW of a fairly bright field star. Moving eastward and directly south of another field star, I found NGC 2375 which appeared as a larger cloudy haze that did not seem elongated, nor did it have any apparent central brightening. Moving ESE and arriving just ESE of a relatively bright star is NGC2379, which is another fairly large, circular cloud, but this one had a stellar nucleus.
4/22/11 10:04 PM
NGC2385/2388/2389 Galaxy Cluster Gem Mag 15
RA 07h28m28s Dec +33°50’16”
At 363x, the westernmost galaxy is NGC2385, which is located in a lonely area and is quite faint. I could barely see it with direct vision; averted vision improved the view, but in either case it was a very small faint hazy spot. Moving to the east, the next galaxy is NGC2388, located SW of a field star. This is also a faint galaxy, although a little larger and brighter than the previous member, and with a slightly elongated halo. The last galaxy, NGC2389, is directly south of a fairly bright star, and is of similar brightness overall to the previous galaxy (at least in the halo), but this one had a little bit of core brightening. Averted vision revealed a slightly elongated halo.
4/22/11 10:36 PM
NGC2872/2873/2874 Galaxy Cluster Leo Mag 13
RA 09h25m43s Dec +11°25’56”
Observed at 363x. This is a very tight grouping, and I was only able to see two main members, and my map showed all three so close together that I was unclear as to the identities of what I saw. I saw two fuzzy areas. One had a bright compact core and a slightly elongated halo. The second was larger and more elongated, with core brightening – although less bright than the first – and averted vision revealed a stellar nucleus. I could not distinguish a third galaxy, so it was either too faint, or overlapped the first two.
4/22/11 10:52 PM
NGC2943 Group Galaxy Cluster Leo Mag 14
RA 09h38m33s Dec +17°01’53”
I toured this group at 363x. The main galaxy, NGC2943, is SW of an apparent double star, although my map shows it as a star with a galaxy next to it. NGC2943 is a fairly large, slightly elongated glow with a brighter core area. Just to the west of this galaxy is NGC2941, which is more difficult to see, but was visible as a small, dim fuzzy spot with little central brightening and a slightly elongated halo. Moving westward, I found NGC2933 located just north of a pair of stars, one of which is quite bright. NGC2933 is very faint and quite elongated, a thin spindle. Moving further west, I found NGC2928, which is also very faint – almost invisible – and averted vision revealed some elongation and no apparent central brightening. Returning to NGC2943 and slewing eastward, I found NGC2946, which is just north of a row of 3 N-S stars. This galaxy was also extremely faint, with a tiny bit of central brightening yielding to a dim, diffuse halo that seemed a little elongated. Next I slewed to the SE to find NGC2949, and despite using a map to pinpoint the location, it was too faint to see. So, I ended this tour with five confirmed galaxies.
4/22/11 11:15 PM
NGC2950 Galaxy UMa Mag 11
RA 09h42m35s Dec +58°51’04” Size 3.2’x2.1’
At 363x this modest-sized galaxy was bright, with a bright, tight core and a nearly stellar nucleus. The halo was relatively small and slightly elongated. There is a bright star to the west of the galaxy, and between this star and the galaxy, just off the halo, there is an arc of three much fainter stars.
4/22/11 11:28 PM
NGC3003 Galaxy LMi Mag 11.7
RA 09h48m36s Dec +33°25’17” Size 5.9’
At 363x this galaxy is fairly large and quite elongated; it seemed to be a nearly edge-on spiral. The central core area was only slightly brighter than the halo and was also elongated. The halo seemed to have an irregular shape, and the eastern side seemed wider or more bulged-out than the western side. Near the western edge of the halo, I was able to detect with averted vision a faint field star superimposed on the halo. Also, to the west of the halo, I saw a curving arc of four stars.
4/22/11 11:38 PM
NGC3184 Galaxy UMa Mag 9.8
RA 10h18m17s Dec +41°25’27” Size 6.9’
At 363x this appeared to be a large, face-on spiral. The galaxy seemed to have low surface brightness overall, but I could discern some of the spiral structure. I could make out most of one outer arm, which circled around the west side and ended towards the north edge, where there is a bright field star that overlapped the end of the arm. I was unable to trace another arm completely, but the rest of the halo exhibited a broken character, with knots, gaps and a swirling character that suggested spiral structure. The nonstellar core was only a little brighter than the halo.
4/22/11 11:50 PM
NGC3198 Galaxy UMa Mag 10.4
RA 10h19m55s Dec +45°33’00” Size 8.3’
Observed at 363x. This galaxy is substantially elongated, with an irregular perimeter to the halo. The core is fairly large and only slightly brighter than the halo. The halo was mottled and the two tips of the halo did not taper smoothly, but had a ragged appearance. The SE portion of the halo seemed to bulge out more than the opposite end. Just to the north of the galaxy there is a bright star. A pair of fainter stars appeared to the SE.
4/23/11 12:02 AM
NGC3310 Galaxy UMa Mag 11.1
RA 10h38m46s Dec +53°30’12” Size 3.6’x3’
At 363x this galaxy gave a peculiar impression. There is a dominant core, which was large, bright and circular and also exhibited mottling. The halo protrudes only a small distance outward from the core. The impression I got was of two objects superimposed, as if there was a bright blob superimposed on something larger and fainter. There are a few field stars north of galaxy, one faint one nearby, then a brighter one, and a few others further away from the galaxy.
4/23/11 12:10 AM
NGC3486 Galaxy LMi Mag 10.3
RA 11h00m24s Dec +28°58’32” 6.9’x5.4’
Observed at 363x. Nice. This galaxy had a mottled core surrounding a stellar nucleus. The fainter halo dissipated gradually into the background, and averted vision revealed more extension than the initial direct vision impression. Careful examination suggested slight elongation to the halo, a mild oval shape.
4/23/11 12:30 AM
NGC4365 (and others) Galaxy Vir Mag 11.5
RA 12h24m28s Dec +07°19’04” Size 6.2’x4.6’
At 363x, NGC4365 had a bright concentrated core and a moderate-sized halo which was slightly elongated. There are several other galaxies nearby. Slewing NE, I found NGC4366 which is a very faint haze. Moving further NE, I found NGC4370, which was a bit brighter, with an elongated halo and somewhat brighter core. Two bright stars were located SE, and there is supposedly another faint galaxy near one of these stars, but it was too faint to see. Returning to NGC4365 and slewing to the SW, I saw four more galaxies, all easily visible, but I decided not to describe each in detail.
4/23/11 12:48 AM
NGC4526 Galaxy Vir Mag 9.6
RA 12h34m03s Dec +07°41’58” Size 7.2’x2.3’
At 363x this appeared as a nice, bright, edge-on spiral, with a large, bright core that seemed to be a little lumpy. The halo was quite elongated and extended. There is a field star just off the center of the galaxy to the south.
4/23/11 12:53 AM
NGC4535 Galaxy Vir Mag 10
RA 12h34m20s Dec +08°11’51” Size 6.8’x5’
At 363x this appeared to be another face-on spiral galaxy. It was large with rather low surface brightness, and I could see 6 stellar pinpoints superimposed on the halo, one of which seemed centered and so could have been the nucleus of the galaxy. The remaining 5 were undoubtedly superimposed field stars. The halo exhibited structure, including knots and gaps and an overall swirling character, but I could not explicitly trace spiral arms.
4/23/11 1:01 AM
NGC4546 Galaxy Vir Mag 10.3
RA 12h35m30s Dec -03°47’37” Size 3.5’x1.7’
Observed at 363x. This galaxy is quite bright, with a bright concentrated core and a nearly stellar nucleus. The halo was moderate in size and elongated. There is a pair of field stars to the SE and another star to the NW.
4/23/11 1:10 AM
NGC4570 Galaxy Vir Mag 10.8
RA 12h36m54s Dec +07°14’46” Size 4.1’x1.3’
At 363x this is an appealing edge-on spiral. It has a bright compact core and a stellar nucleus. The halo is thin and long, oriented SSE to NNW and the NNW tip point towards a bright field star. A nice spindle-shaped galaxy.
4/23/11 1:16 AM
NGC4636 Galaxy Vir Mag 9.6
RA 12h42m50s Dec +02°41’16” Size 6.2’x5’
At 363x this has the appearance of a nearly face-on spiral. It has a large, broad nonstellar core and the halo diffuses gradually into the background. Averted vision increases the extension of the halo. I saw some mottling in the halo but no other evidence of spiral structure. The halo was brighter on the south side of the core compared to the north side of the core. The south and north sides of the halo are bracketed by two bright stars. A faint star borders the west side of the halo and a brighter star borders the east side of the halo.
4/23/11 1:23 AM
NGC4643 Galaxy Vir Mag 10.6
RA 12h43m20s Dec +01°58’39” Size 3.4’x2.7’
At 363x this galaxy has a bright nonstellar core with a small elongated halo. There is a bright star off the NW edge of the galaxy.
4/23/11 1:28 AM
NGC4660 Galaxy Vir Mag 10.9
RA 12h44m32s Dec +11°11’25” Size 2.8’x1.9’
At 363x this galaxy exhibited a compact core with a nearly stellar nucleus and a small elongated halo. It was quite bright, mostly due to the core. I was unable to see the companion galaxy, IC3711, possibly because by now the 67% gibbous moon had just begun to rise.
