Wednesday, August 13, 2008
First light for the DMK 21AF04 AS
At the moment I'm testing my new camera, the DMK 21AF04 AS. I first tried the camera on the Coronado PST, and I was surprised by the result. The first image is a typical frame I selected from the 1-minute movie I shot from a prominence. The second image shows the stacked (600 frames) and processed version.
I will inform you about the equipment set-up and the stacking/processing software in the near future. Right now I'm busy reading the software manuals and experimenting with the few movies I recorded. In the end this monochrome camera will be used to shoot detailed images of the Moon, the Sun in combination with the Baader Herschel Prism/Continuum filter and the Sun in H-Alpha with the Coronado PST. I will keep you updated!
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.
Sunday, July 13, 2008
Eye-relief for my 12-inch telescope
Introduction
About one and a half years ago I bought a 12-inch telescope for deepsky observing, an f/5.3 Newtonian telescope from Orion optics UK. The tube is mounted on a dobsonian rocker-box and equipped with the Argo Navis Digital Telescope Computer. During the past 18 months I have put together my set of eyepieces for this telescope. I had four major criteria for selecting the eyepieces:
1. High quality
2. Large true fields of view
3. Weight between 400 and 800 grams
4. Lots of eye-relief
All selection criteria were important, but the most important was number four, eye-relief. In this article I will tell you why these criteria were more or less important to me, which eyepieces I finally chose and why I chose them.
Thursday, June 05, 2008
Xi Bootes in Little Cygnus
On the evening of May 9th 2008 Leo and I got together to observe a series of double stars in Bootes, inspired by an article in June's Sky and telescope (Binaries in your Bootes). In the period between the beginning of May and the end of July it doesn't get really dark at night, but for observing double stars or asterisms, this proved to be not a problem at all. We started at 23.00 hours local time (UT + 2hrs). In three hours time we observed and sketched about six doubles in Bootes and two asterisms, one in Bootes (Picot 1), the other in Ursa Major (Ferrero 6). The highlight for me that night was Xi Bootes. This colorful double lies about 8 degrees east of Arcturus. The Yellow primary star shines at magnitude 4.8 and it's magnitude 7.6 orange companion lies at a position angle of 315°. The separation is 6.3". Through the 17mm Nagler the double looks fairly close (scale from "Double Stars for small Telescopes" by Sissy Haas). When looking at Xi Bootes through the 17mm Nagler, the double seems to be part of an asterism that looks like the constellation Cygnus, only much smaller. Xi Bootes is placed at the position of Deneb, the tail of the swan. We decided to call the asterism "Little Cygnus". On the sketch below the asterism is oriented West-East. At the tail you find Xi Bootes. Three white stars oriented north-south represent the wings of the little swan. A white star to the east (accompanied by a dimmer companion) is at the position of the head of the swan. The yellow star to the eastern edge of the field of view is just a bright field star. It is no part of the "Little Cygnus" asterism.
The sketch of "Little Cygnus " and Xi Bootes was made using the 300mm f/5.3 Dobson and a 17mm Type4 Nagler. The magnification is 94x and the field of view is 52'. At the telescope I made a sketch on white paper using a HB led-pencil. This sketch was scanned and processed in Photoshop. I colored the double star (and the field star to the east) using the tutorial described on the website of Jeremy Perez ( http://www.perezmedia.net/beltofvenus ). This is the first time I experimented with this technique, and I am very pleased with the result. It produces a realistic image and resembles what you see through the eyepiece. In the future I will try to use this technique for sketching more double and multiple stars.
Saturday, March 29, 2008
Prominences and filaments
Today I went outside with my Coronado PST to do a little solar observing. I observed for about one and a half hour and from 13.50 until 14.20 local time I made a sketch of the Sun using different Red, Yellow, Orange and Grey soft pencils. The paper I used was black sketching paper. I also used three different erasers. As a smudging tool I used my finger. The technique I used was adapted from the book "Astronomical Sketching" by Handy et al. The picture below shows the result I got from my observing session. Overall I counted three groups of three prominences each. One on 3 o'clock, another on 4 o'clock and the last between five and 6 o'clock. On 9 o'clock I detected a lonely prominence. On 3 o'clock I saw two prominences that were completely detached from the solar disc. The same goes for two prominences at almost six o'clock. In the 4 o'clock group and the six o'clock group I saw two prominences looking like a mushroom. I think they are called "hedgerows" by official classification. I also found two filaments. One was a dark "S" formed structure about 1 o'clock; the other was a small half circle around a much lighter pelage at 5 o'clock. The sketch was made using a low cost 15 mm Ultrawide (66 degrees) eyepiece with long eye-relief from Sky watcher. The picture was much clearer and showed more detail than my 15mm Vixen Lanthanum. The latter is absolutely darker, and much more expensive (about 5 times the price of the Skywatcher 15mm). Other eyepieces that were used during observing were the 21mm Denkemeier, 12 mm Nagler T4 and the 9mm Ultrawide from Skywatcher. I hope the Sun will start showing a little more details in the H-Alpha band in the next few months. I really enjoyed the H-alpha sketching. It makes you look very careful for details.
Wednesday, February 13, 2008
Star party at Bel Any
Last weekend we had a small star-party in Any Rieux Martin in the northern part of France. The weather was just wonderful and on Friday and Saturday night we could observe through the night. I had a lot of first time viewings of some fantastic objects like the Flame Nebula and the complete Rosette Nebula. I also had the chance to observe a few Messier objects near the southern horizon (M 79, M 41 and M93). A detailed report will be logged later on this month, but here are a few images that were taken on the first evening. Click on the images to enlarge.
Monday, December 24, 2007
22 degree halo around the Moon
I just went outside and saw this huge 22 degree halo around the Moon. Very impressive. It even had Mars within the halo. Also notice how dark the sky is inside the halo. The images were shot with the Nikon Coolpix 4500 mounted on a tripod. Exposure time 8 seconds. I also used a wide angle lens for the coolpix. This was the first time ever I saw such a large halo around the Moon. 
