Category: Deepsky log
Tuesday, February 08, 2011
Observing Orion
In the last few weeks I observed a few interesting objects in Orion. I started in januari with Collinder 70, Orions Belt. Last week I had a look at Collinder 69 and Collinder 72, one of Steven James O'Meara's hidden treasures. Today I added another three wonderful objects to my sketchbook: Rigel, Betelgeuse and Collinder 65. Rigel was observed with the 12 inch dobson. The double star did not show itself as a double initially, due to a lot of turbulence in the tube (the scope was just outside for a few minutes. However, after switching on the fan, the weaker B companion popped into view, just like that. The image was stable right from the moment the fan started to make a laminar flow in the 12-inch tube. Amazing. Betelgeuse was also observed with the twelve inch, and the deep orange color was simply overwhelming, especially at lowest power. However, in the 85mm Zeiss, the color looked even much deeper than in the 12-inch.
Collinder 65 is a large open cluster, which actually belongs to Taurus, but lies on the Orion-Taurus border. I observed and sketched this large open cluster (3.3 degrees) using the Skywindow and the 8x42 Orion binoculars, field of view 8.2 degrees. Until a few days ago I didn't know this cluster was actually there, but when scanning the area between Collinder 69 and Messier 1, you cannot miss it. You immediately will recognize it as a cluster.
In the next few weeks I hope to publish my observing reports and sketches on http://www.starobserver.eu On the map below you can see where the objects I observed can be found.
image from Voyager by Capellasoft
Posted by Math on 02/08 at 03:14 PM |
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Sunday, August 03, 2008
Update on the spectral riddle in the "Rocking Horse"
I would like to thank Jim Kaler (Prof. Emeritus of Astronomy, University of Illinois), for helping me with my “spectral riddle” in NGC 6910, the Rocking Horse cluster. Here’s why the B1 supergiant looks yellow visually instead of bluish-white what you would expect from a B-type star.
As you know it is in the middle of Cygnus, near Gamma Cygni, not far off the galactic plane (you can see my wide angle picture at http://www.astro.uiuc.edu/~kaler/sow/sadr.html). As such it is subject to a great deal of interstellar extinction and reddening from interstellar dust. The dust selectively absorbs and scatters blue light (roughly 1/wavelength), so when you look at a star thru dust it will appear redder than it really is (basically the same reason the sun is reddened at sunset). The intrinsic B-V color of a B1.5 Ia supergiant is -0.2. The observed color is 0.83, about the color of a K0 dwarf or a G5 giant, so the star appears yellowish to the eye.
The whole cluster is highly reddened in fact by about the same amount. The “color excess” (E) is the observed minus true color, which is about 1.0 for this cluster. The absorption at V is usually taken as 3.2E, so Av (abs at V) is 3 magnitudes. If there were not dust, a 7th magnitude star would appear 4th magnitude, and the cluster would be visible to the naked eye. Good observing on your part to notice that. You can see the effect in many other distant clusters near the galactic plane.
Jim Kaler
Thanks again!
Sunday, July 20, 2008
A spectral riddle in the Rocking Horse
In the night of July 13th/14th 2008 I had a short observing session with the 300mm Dob. I took a quick peek at a few old friends (M27, M29, the Blinking Planetary and 16 Cygni) trying out my new 35mm Panoptic. While sweeping through Cygnus, I noticed a bright, small clump of stars North-Northeast of Gamma Cygni. It was very easy to spot with the 35mm Panoptic. I increased the power to 230x with the 7mm Pentax XW, and I was looking at a wonderful little asterism of stars that, as a group looked like a little dog or horse. I made a rough sketch of this object, and when I later checked the sketch with my planetarium program (Voyager), it proved to be NGC 6910, an open cluster from the Herschel 400 list. According to some sources on the Internet, NGC 6910 is also called the Rocking Horse cluster. I had never heard about it or observed it before, so my first impression that it looked like a dog or horse, was not that strange. Others thought of it as a little horse as well.Where can you find NGC 6910? The map below should give you a rough idea. Just center your telescope on Gamma Cyngi and move just about half a degree north-northeast. There you will find this nice clump of stars.
(Image from Voyager 4.5, http://www.carinasoft.com)
When you start looking for NGC 6910, bear in mind that it is a small cluster, only 7' in diameter, but then again, at lowest magnification it jumped out at me in my 12-inch scope. With the 22mm Nagler (fov 68') I already saw the complete outline of the little horse, and with the 7mm at 230x I could see a few dimmer, magnitude 12 stars. NGC 6910 is a Y-shaped cluster oriented northwest southeast. I counted between 20 and 25 stars but its always difficult to tell which do belong to the cluster and which are not included. The two brightest stars looked definitely yellow and are from the 7th magnitude.
There is however something that riddles me about these two yellow suns. According to all planetary programs and Internet databases, the Northernmost of the two stars is SAO 49556, a spectral type K1III, which explains the yellowish color. The southernmost of the two is SAO 49563 (or V2118 Cygni), a variable star of spectral type B1.5Ia. Normally I would think that a B1 star shines Bluish or at least mainly white, and not yellow. I checked other observing reports and I found that Sue French's (Celestial Sampler, page 132) reports:
At 87x, two yellowish stars of 7th magnitude and a pearly, split chain of eight 10th magnitude stars unite in a Y-shaped pattern about 5' long.
Sue sees two yellow stars as well, so I'm very curious why this B1 star seems to appear yellow instead of white. Does it have something to do with the Variable character of the star? Maybe one of you out there can help on this one.
Anyway, visually it is a very interesting group, so I made a sketch. The sketch below was made with the 300mm dob, a 7mm eyepiece (fov 18') giving a magnification of 230x. South is up and west is to the left. The next time when you're in the area observing, check out on NGC 6910 and let me know which colors you could see.
Tuesday, December 18, 2007
M 103 in Cassiopeia
On December the 16th I observed M103 in Cassiopeia with the 300mm f 5.3 dobson. This wonderful little cluster stands out well from the surrounding star field, and looks like a small Christmas tree. I counted 27+ stars in an area of 7’ diameter. There are many triangles and other asterisms visible in M103. This makes the sketching a lot easier. The sketch below was made using the 7mm Pentax. The faintest stars were added with the help of the 7mm Pentax. I could not detect any glow of unresolved stars, but I sometimes saw very faint stars popping in and out of view with using averted vision and a black cloak over my head. 
Sunday, September 02, 2007
The Mini Coathanger
On the evening of Thursday August 23d, I had an hour of clear skies, so I quickly got out with my Sky-Window and the 15x80 Vixen binoculars and the 85mm Zeiss refractor equipped with the 20-60x-zoom eyepiece. I wanted to have a look at an asterism called the Mini Coathanger (STAR 22 from Phil Harrington’s Small Telescope Asterism Roster) in Ursa Minor. The Mini Coathanger, which looks very much like his big brother the Coathanger in Vulpecula, can be found at RA 16:29.0 and DEC +80.13. I always start the search at 16 Zeta Umi. About 2 degrees northeast of this bright magnitude 4 star, a diamond-shaped group of stars can be seen. At the Northern tip of this diamond shaped group STAR 22 can be found. The Mini Coathanger is made up off 11 almost equally bright stars, most of them of the 10th or 11th magnitude. The asterism is 15’ wide. In the Millennium Star Atlas, the whole asterism can be found on page 1046. That night, I started my observing session at 21.00 hours UT. The seeing from my backyard was only 5 on a scale of 10. Most bright naked-eye stars were blinking like crazy. The transparency and sky darkness weren’t too good either. I couldn’t see all seven stars of Ursa Minor, so the limiting magnitude was well below 5. However, with the 15x80 I quickly located the diamond shaped asterism, but the Mini Coathanger stayed invisible. After observing for a few minutes, I started to see a little bar of four or five stars, that form a part of the Mini Coathanger. The stars were very faint, and I could not see the complete asterism, not even with averted vision. Then I switched to the 85mm Zeiss. At 20x the bar of stars already looked a bit brighter, and seemed easier to identify. Zooming up to 60 times, using averted vision, I could see the whole asterism, the bar and hook. I could not detect any colour in the stars. After observing for 20 minutes from under a black hood, I could see the whole asterism with direct vision. I made the sketch below to using the 85mm refractor and the eyepiece at maximum zoom. The field of view at 60x is about 1.25 degrees, but I only sketched the central part of the field of view. Before I finished my observing session I switched back once again to the 15x80 binoculars. This time, using the black hood and averted vision, I still could not identify the whole asterism with the 15x80.
At 22.00 hours UT I packed up and went inside (had to work the next day), enjoyed my cup of coffee and put down a few notes. Looking back at the short observing session I can definitely say that the refractor with its 85mm aperture shows stars of the 11th magnitude much easier than the 15x80 binoculars. With the big binoculars, you use two eyes, which should compensate for the 5mm difference with the 85mm Zeiss. But in the end, I think that the higher magnification (you start at 20x with the Zeiss) makes the difference. The slightly higher magnification gives a little more contrast. If you zoom in to 60x, the 15x80 can in no way keep up with the views the refractor shows. However, I will try to hunt down all the asterisms on Harrington’s STAR list using both instruments. They are ideal for short observing sessions. Both instruments are mounted on video tripods permanently, so I only have to take them into the garden and I’m ready to go!
Friday, August 24, 2007
NGC 7510, a very distant open cluster in Cepheus
At the border of Cassiopeia and Cepheus, near M52, a whole group of open clusters can be found. One of them is the magnitude 9.2 NGC 7510. Last Saturday, August 11th 2007, I decided to revisit this small, (6’ in diameter) open cluster, and make a sketch at the eyepiece. 
Image from "Where is M13?" by Think Astronomy
To observe NGC 7510 I used the 300mm Dob with the 21mm Denkmeier, the 12mm Nagler and the 7 and 5mm Pentax XW. After locating it with my Argo-Navis, I immediately recognized the small and rich open cluster, even with the lowest magnification (76x). The familiar arrowhead shape is something you will not forget, once you’ve seen it. At first glance, NGC 7510 looks very small indeed. This is in part because of its distance. NGC 7510 lies in the Perseus Arm of our galaxy, approximately at a distance of 10.200 light-years. This makes it one of the more distant open clusters. However, would you place NGC 7510 at 440 light-years, where we find the Pleiades, it’s apparent size would be 1.55 degrees! It would 30% larger than M45.
After increasing the power to 320x (5mm Pentax) I noticed that a lot of stars I’d seen on previous occasions stayed invisible. In fact, the transparency proved to be horrible. When comparing the sketch with a printed map from SkyTools2 the next day, the faintest star I plotted using my 12-inch scope was only magnitude 13.3. From the same location, my own backyard, I reached magnitude 13.5 with the 8-inch TAL 200K, on a very good night a few years ago.
Anyway, I made a sketch at the telescope with just a HB pencil, eraser and a piece of sketching paper. I did not plot all the field stars. I only concentrated on the possible cluster members. It is always very hard to recognize the real border of a cluster, and to determine which stars do belong to the cluster and which don’t. But I’m not the only one! When checking different entries in my observing guides I noticed that the values for size, numbers of stars and even magnitude vary a lot from one another. The eyepiece used for the sketch was the 5mm Pentax XW (320x). It took me 45 minutes to observe NGC 7510 and to complete the rough sketch. The next morning, with the help of my rough sketch and the notes I recorded on my Ipod, I made a new, final sketch to file in my observing log. For this final sketch (see image below) I used black paper and very a very soft white pencil. I only plotted the stars I had on my original sketch. I used a printed map from Skytools2 to check the positions of the stars and to the check the limiting magnitude for that night.
As you can see, I counted about 19 stars in the cluster. There was no real color visible in the stars, though I suspected a little color in the brightest. It seemed a bit yellowish, but I must have been wrong because when checking my observing library, I found out that its Lucida is a luminous blue B1.5 III giant (Sky Vistas, page 78, Crossen and Rhemann). The sketch is made with north up and east is to the left.
Wednesday, August 08, 2007
Deepsky observing with an Owl.......
Last Saturday I had a great time together with Leo. Together we observed not only some well-known deepsky objects, but also a few "new" objects. I used my 300mm Dob and got a chance to test my two new eyepieces, the 21mm Denkmeier and the 5mm Pentax XW. Leo observed with the TAL 250K. The outside temperature was between the 15 and 20 degrees Celsius. The seeing was average, but the transparency was not too good. We barely could make out all the 7 stars of Ursa Minor. But after months of rain and clouds, you are happy with every observing opportunity, so we took it with both hands. The waning last quarter Moon came up around 00.00 hours and stayed out of the way (behind some trees) until 03.00 hours. Anyway, we had a good time observing the deepsky from 22.30 until 03.00 o' clock. 
Tuesday, August 07, 2007
The Red Necked Emu
On Saturday July the 15th, Leo and I finally had a good evening of observing together. We enjoyed hunting some deep-sky objects, he with the 4-inch Takahashi and I with my 15x80 Binoculars mounted on the SkyWindow. We started of with two very large clusters near the Serpens Cauda / Ophiuchus border, NGC 6633 and IC 4756. These two contrasting clusters are also included in O'Meara's "Hidden Treasures", under the numbers HT 92 / HT 93. With my 15x80 binocular (field of view 3.5 degrees) I could not see both clusters together. I had to turn the SkyWindow from left to right and back again to compare both clusters, but I noticed immediately how different these two open clusters are. I estimated IC 4756 about 45' or 50' in diameter. In a trapezium of 4 bright stars I count at least 50 weaker stars. NGC 6633 looks much more compact, about half the size of IC 4756. However, the individual stars are brighter, and are grouped in a kind of small elongated circle, and a few long straight streamers of stars. These two clusters are wonderful objects for binoculars. Our next stop was Phil Harrington's STAR 26 ( STAR=Small Telescope Asterism Roster), the Red Necked Emu in Cygnus, The Swan. I had seen it once before in my 4-inch refractor a few years ago, so I knew what I was looking for. The Red Necked Emu looks like a giant propeller with three blades, about 1 degree in diameter. Just start at Gamma Cygni, the orange star at the heart of Cygnus, and move towards Albireo along the neck of the Swan for 2.5 degrees to 34 Cygnus. From there move about 1.5 degrees in the same direction to arrive at 29 Cygnus. This star marks the tip of the Emu's tail. On the image below you can see how the Emu is oriented in the sky. Through my 15x80 it was very simple to find. I think this object is best in 80 to 100 mm instruments, with a large field of view. This strange bird is called Red-Necked Emu because all the stars he consists of are white-bluish, except one orange-reddish star in its neck. This is very easy to see.
Click to enlarge
After this I first freewheeled a little through the Milky Way in Cygnus, a wonderful experience with binoculars. M 29, Albireo, Omicron 1 and 2, are just a few of the stops I made. After that I also made a little tour through Vulpecula: The Coathanger (Collinder 399) The Dumbbell (M 27), and the wonderful open cluster NGC 6940. Although not very well resolved, NGC 6940 stood out well from its surroundings, however I like this object more in my 300mm Newtonian. From Vulpecula I turned back again into the Swan, passing M 39 and on to Mu Cepheus, the Garnet star. In this area we looked at a few open clusters, but because we had some problems identifying them, we will have to revisit this area.
Posted by Math on 08/07 at 11:08 AM |
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