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.

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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!

Posted by Math on 09/02 at 02:47 AM | (0) Comments | filed in: Deepsky log | Print
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.

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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.

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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.


Posted by Math on 08/24 at 02:57 PM | (0) Comments | filed in: Deepsky log | Print
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.

Posted by Math on 08/08 at 01:10 PM | (0) Comments | filed in: Deepsky log | Print
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.


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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 | (0) Comments | filed in: Deepsky binocular | Deepsky log | Print
Saturday, July 14, 2007
Observing hidden treasures.........
Last night it was clear between 11 and 1 o clock (local time) and I had a quick look at some deep-sky objects with just to test my new eyepiece, the 21mm Denkmeier. In my dob, the 65-degree eyepiece gives a magnification of 76x and a true field of view of 51'. I pointed the eyepiece at M 27 and although it wasn't really dark (grey nights during the May-July period), it was quite an impressive sight. M 27 is really big, even at low powers, and with the UHC filter the Dumbbell shape is very obvious at first sight. The 21mm Denkmeier seems to be very "transparent", letting through much more light than the 20mm and/or 25mm Vixen Lanthanum. The stars where sharp right to the edges although I think that there is a little pincushion distortion along the edges. What I really love about this eyepiece is the generous 20mm eye-relief. Even with my glasses on, I can take in the whole field of view at once.

Posted by Math on 07/14 at 10:54 AM | (0) Comments | filed in: Deepsky observing | Print
Wednesday, July 11, 2007
Hidden Treasures
A few weeks ago I got a new book from Steven James O-Meara: “Hidden Treasures”. This is his third Deep-Sky Companion he wrote and it is definitely my favorite read at the moment. After the well known “Messier Objects” and “Caldwell Objects” this new book, Hidden Treasures, is again about 109 deep-sky objects, but this time about objects which are not included in the Messier or Caldwell catalogs. Some of them are well known, but there are a lot of objects which were more or less new to me.

Again the whole range of deep-sky objects is included, Galaxies, Planetary Nebulae, Star Clusters (open and globular), Asterisms, Bright Nebulae, Dark Nebulae and even a High-proper motion star. Steven James O’Meara is getting better and better. I like the way he writes his deep-sky companions. There’s always a lot of information about each individual object (history, observing the object, how to find it, and up to date scientific information), and for every object a finder-chart, black and white image and a sketch. The information you get in this book is also fully consistent with the two other books in this collection.

I can highly recommend all three of them. In the English language, they are by far the best observing guides around at the moment, and Hidden Treasures is with almost 600 pages packed with information on 109 deep-sky objects the crown on this wonderful series (until now).


                    



Posted by Math on 07/11 at 10:49 AM | (0) Comments | filed in: Books and magazines | Print
Thursday, June 28, 2007
Watery Moon
During the last few weeks the weather hasn’t been very kind on the observing front, so I cannot bring you much news about deepsky, solar or lunar observing. Most of the time it has been cloudy or completely overcast. Monday night however the clouds opened up for an hour, and I got a quick glimpse of the Moon with my binoculars. This image of the Moon was taken just a mile from where I live near the water tower.

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Click to enlarge

Posted by Math on 06/28 at 11:31 AM | (0) Comments | filed in: Lunar scraps | Print
Tuesday, June 26, 2007
Mount Doom....
Last week we were walking through the fields in our hometown. As you can see on the image below, about an hour before sunset we were treated on a very special sight, the Sun “touching” the top of a big cloud. The view instantly reminded us of Mount Doom, the big volcano in Mordor (from The Lord of the Rings). Hmmmm….. maybe finally something happening in Landgraaf, Netherlands tongue wink

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Click to enlarge

Posted by Math on 06/26 at 11:16 AM | (1) Comments | filed in: Solar scraps | Print
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