Wednesday, April 30, 2014

Springtime galaxies

Last weekend saw the arrival of a reasonably good night, naturally I took the opportunity to look for some objects I wanted to see for the first time or get drawings of. So I drove out to the airstrip and set up the 15-inch while the sun was still up. After assembling the telescope and setting up the computer, it was time to collimate it and allow the cooling fan time to get the primary mirror closer to the falling ambient temperatures after sunset. Once it became dark enough to see some bright stars, I initialized the digital setting circles and the night's observing began. There was only about three and a half hours to observe under dark skies, because the waning gibbous moon rose just before midnight. So I concentrated on a few objects of interests in the constellations Lynx, Sextans and Pyxis.
NGC-2818 is an open cluster and planetary nebula in the southern constellation Pyxis with a planetary nebula appearing among its stars, like the Messier object M-46 in Puppis. While the open cluster was underwhelming through the murk near the southern horizon, the planetary nebula was easy to make out with an O-III nebula filter in place. It was fairly bright and large, looking somewhat apple core or barbell shaped. Shining at 8th magnitude and spanning nine arc-minutes, the star cluster is not particularly spectacular, but this planetary nebula would be impressive if it was higher in the sky from my location. It shines at a magnitude of 11.6 and is 35 arc-seconds across. I saw no other signs of structure or the central star that excites the nebula's gasses into fluorescing in visible light. To distinguish it from the star cluster, the planetary nebula often is referred to as NCC-2818A.

NGC-2537 is one of many galaxies in the northern constellation Lynx, which is now high in the skies after dark. This is an irregular dwarf galaxy that has peculiar bright patches in it that create the appearance of a bear paw, hence the nickname "Bear Paw Galaxy." It is also known as Arp-6 This object is an irregular system of type Sd, with a magnitude of 11.7. It's fairly small apparent size of 1.7 arc-minutes gives it a fairly high surface brightness. Also in the field can be found two other galaxies, one being NGG-2537A, a background galaxy at least 20 times further away than NGC-2537 in the foreground. The other is IC-2233, a faint edge on galaxy that eluded my 15-inch, probably because the skies were not very transparent that night. It lies 18 arc-minutes to the SE of NGC-2537 and forms a pair with NGC-2537A, which is unrelated to IC-2233. NGC-2537A was visible as a faint, round, fuzzy spot, which is all that can be seen of this very remote face on-spiral galaxy.

NGC-2549 is a lenticular galaxy of type SO also located in Lynx, but larger and brighter than NGC-2537. Shining at magnitude 11.2 and an apparent length of 4.2 arc-minutes, this galaxy has a relatively high surface brightness. This galaxy appears as an elongated object with a bright core, but is otherwise featureless because it's not forming new stars due to a lack of gas and dust. As a consequence, NGC-2549 mostly populated with older yellow and red stars.

In the inconspicuous constellation Sextans lies a number of galaxies modest telescopes can reveal under good skies. However, the murky and light polluted skies of my area demand a fairly large telescope to merely see many of these galaxies that are visible to smaller telescope at dark sites. NGC-3044 was however an interesting find that showed up quite well as the sky conditions worsened as the night progressed. Oriented south-southwest to north-northeast, this 12th magnitude edge-on galaxy appears as a slash of faint light some 5-arc minutes long. It was quite easy to make out at 142X. NGC-3044 is a SBc barred-spiral galaxy that resembles the Draco galaxy NGC-5907, but much smaller and fainter.
Another galaxy in Sextans worth a look is the face-on Sc type spiral NGC-3423. Small and round, this galaxy has a brighter center and spans some 3.8 arc-minutes of sky and has an overall magnitude of 11.2. This object bears magnification well, a point in it's favor because it is quite small as the drawing shows for a visual observer. I did not see any evidence of it's numerous H-II regions or it's spiral arms.
While at the airstrip, I brought along a red-filtered lap top computer which was helpful in locating these objects. I also tried out a shelter I made to keep the computer dry and warm enough to function properly, it was quite cool and very damp that night. Hazy skies and poor seeing were the order of the night, and the moon rising at midnight forced an end to observing deep sky objects for the night. I did get another look at the fading supernova in M-82, Mars and Saturn.; The seeing was certainly not the best for the planets, but with it being more often than not overcast locally, I take any chance I can get to look at them.


Sunday, April 6, 2014

Winter and spring deep sky objects

Winter has finally drawn to a close and with the departure of the cold comes hordes of galaxies as soon as it becomes completely dark. Nevertheless, some winter objects remain in view and therefore I observed a few of them before they are lost in the glare of the Sun. Along with the arrival of warmer temperatures nights are getting shorter and all of the major planets are visible now at some point during the night. It is still stormy and murky most of the time, but a few good nights have come along, good enough to make taking the 15-inch to a darker skies worth the effort. The drawings shown here were made over a two week period last month. 
The Ursa Major galaxy M-82 is one of my favorite galaxies, but recently a bright Type 1A supernova has appeared there. I have been following it ever since I learned of it's eruption. Reaching a peak brightness of about magnitude 10, it was unmistakably visible even at home despite the heavy light pollution. Here in this drawing the supernova was shining at about magnitude 11.7 as it fades towards invisibility. The last time I examined M-82 the supernova was still visible, but now it's too faint to still see from my house at a magnitude of 12.9. If you wish to see this supernova, look for it now because soon it will be out of range of all but very large professional telescopes and those equipped with ultra-sensitive cameras. It is quite a thrill to witness an event that actually happened 12 million years ago.
 The southerly constellation Columba the Dove is poorly seen if not invisible from the U.S. and Europe, but contains both Milky Way and extra-galactic objects within it's confines. The brightest and best of these objects is the bright, small and concentrated globular cluster NGC-1851. It can be seen in small telescopes as a small, round, fairly bright object that resembles a comet with an intense inner core. It's hindered by the low elevation in my local skies, but through my 15-inch it breaks up into stars, resembling a southern version of the Pegasus globular cluster, M-15.
Auriga has many, many open clusters, nebulae and even a globular cluster in it's borders. One such object I have always been interested in is the open cluster NGC-1893 and the emission nebula that surrounds it, IC-410. The sky conditions at the time were quite poor, but when I put a narrow band nebula filter on the eyepiece regions of faint nebulosity appeared. The most prominent was a ring like patch with a darker center and spangled with stars.
While Orion is well known for the Messier objects M-42, M-42 and M-78, it has dozens of less well known objects that are worthy of study. One object I wanted to make the acquaintance of was the ninth magnitude open cluster NGC-2112. Fairly small and perhaps consisting of two dozen stars, it is an inconspicuous object amid the dense star fields and hordes of brighter nebulae and star clusters. It spans 11 arc-minutes and required 227X to distinguish from the surrounding star field.
The bright, rich and large open cluster M-35 is undeniably one of the finest object in the winter sky, and I have observed it many times over the years. It does however share the field of view with a much more massive and distant open cluster that is six times farther away from us than M-35. That star cluster lies some 2,800 light years away. It's some 100 million years old, and had a total population of at least 500 stars across an area about 25 light years across. NGC-2158 normally appears as a small fuzzy comet like spot some 15 arc-minutes away from the center of M-35 and lies at the enormous distance of at least 16,000 light years. To my amazement, it showed partial resolution into stars at my house on a good night, and resolved into a swarm of very faint stars at the club's darker sky site. This star cluster has an age of some 800 million years, the brightest Main Sequence stars having a spectral type of F0. Shining at magnitude 8.6 and an apparent size of 5 arc-minutes, NGC-2158 is worthy of close scrutiny for those with larger telescopes, and makes a nice showing together with M-35 in smaller instruments.
NGC-2420 is another ancient open cluster in Gemini, with a total population of at least 1,000 stars and an age of 1.7 billion years. It is also 3,000 light years from the plane of the Milky Way's disk and is 30 light years across. It's right now some 33,000 light years from the center of the Milky Way, placing it some 8,000 light years away from Earth. Shining at magnitude 8.3 and spanning 10 arc-minutes of sky, this massive and aged open cluster curiously has the same chemical composition of our Sun and Solar System. It readily resolved into stars through the 15-inch despite the rather bad skies that night, and doubtlessly would reveal it's nature to users of 8 and 10-inch telescopes under good skies at dark sites. Most open clusters disintegrate under the relentless gravitational forces of the Milky Way's disk, but NGC-2420's orbit around the galactic center and it's high mass enabled it to hold onto at least 1,000 of it's original compliment of stars. Many red-giant and helium burning stars exist in the star cluster, along with white dwarfs.
As winter gives way to spring, Ursa Major and it's swarms of galaxies near and far rise high into the sky as night falls. The entire constellation is riddled with every type and size of galaxy imaginable, so I opted to concentrate on the brighter ones in Ursa Major's head. NGC-2742 is fairly faint and large, with an obvious nuclear region and a slightly wooly halo at 181X. It is a spiral galaxy of type SC shining at magnitude 11.7 with an apparent size of 3 X 1.5 arc-minutes. It's oval outline is oriented almost exactly east to west. Overall, a nice example of a type-Sc spiral galaxy whose inclination is between face and edge-on. The galaxy NGC-2768 lies 40 arc-minutes away to the southeast.
NGC-2768 is another fairly bright Ursa Major galaxy I have observed before with smaller telescopes. This tenth magnitude object is 8. X 4.3 arc-minutes long and has a bright central core. Unlike NGC-2742 which is forming stars, this galaxy is a lenticular or disk shaped system dominated by old yellow and red stars. It is lacking in interstellar dust and gas from which new stars form, as a consequence it appears more featureless than it's neighbor through the telescope. It also has nearly the same orientation in the sky as NGC-2742.
NGC-2787 is a barred spiral galaxy shining at magnitude 10.9 and has an apparent size of 3 X 2 arc-minutes. This SB-O galaxy was small, oval and had a bright core, though I did not plainly see the central bar at 227X. I had a difficult time determining which way the galaxy was oriented as I made this sketch, perhaps because the bar is nearly at right angles to the rest of NGC-2787's featureless disk.
NGC-2810 is a small elliptical galaxy with a bright center but otherwise it appears as a featureless, circular glow. Shining at magnitude 12.3 and being only two arc-minutes across, this galaxy is one of the less impressive systems in Ursa Major at 227X. I had thought I glimpsed a star like nucleus in this galaxy, but its faintness and small apparent size is due to small size and or lying at an immense distance from Earth.
NGC-2880 is brighter than NGC-2810, shining at magnitude 11.6 and spanning 2 X 1.2 arc-minutes of sky. Like NGC-2768 however, this is a lenticular galaxy of Hubble classification SB-O. It shows it's oval outline and a brighter center, but is otherwise featureless due to the absence of spiral arms or star formation. It does however respond well to higher magnifications and stands out better against the sky due to the much higher surface brightness than NGC-2810.
NGC-2950 is an eleventh magnitude object that spans three arc-minutes in length. It lies next to a convenient guide star for those who star hop to objects. It is either a lenticular or a transitional system between a barred spiral and a lenticular galaxy. What appeared in the 15-inch at 227X was a fairly bright, oval object with a very bright central core. The halo around it was much fainter and the object's small apparent size enabled it to show up well through the worsening skies. Soon after observing this galaxy, it was clear the skies were about to give out. So I observed a few more objects, then took down and packed away the telescope for the trip home.