Posts Made By: Inge Skauvik

Since my last posting under this thread I can boast the sighting of only 5 objects - SSO's (Shallow Sky Objects) rather than DSO's: The sun, the moon, Vega, Arcturus and Altair, all viewed with the naked eye. When I arrived at my vacation site (64 deg. north) 1st of July I couldn't see any star even at midnight, but from the 10th of July the brightest stars could be spotted.

I did an interesting experiment a few days ago, which can be used as an illustration of the importance of a dark sky background. What is needed for the experiment is a polarisation filter (a pair of good polarising sunglasses works ok), the sun must be up and there must be some clouds present on a clear sky background.
In the zone near 90 degrees from the sun the blue skylight is strongly polarised, while the light reflected from the clouds is not. By turning the polarising filter it is therefore possible to adjust the darkness of the blue background, while the clouds remain equally bright. I don't know exactly how much darker the sky becomes when the filter is held the optimum (darkest) way, but I would guess about 5 - 10 times, say two magnitudes surface brightness.
The interesting point for the deep-sky observer is how this affects the visibility of faint cloud patches. Some clouds were completely invisible with the filter in the position letting the polarised light through. Turning the filter 90 degrees showed the clouds easily, in many cases with intricate detail. Generally the view of all thin clouds improved dramatically by blocking the polarised light.
This demonstrates the advantage of observing DSO's from a dark site compared to a location with light pollution. The difference between a 4th and a 6th magnitude sky is tremendous regardless of aperture used. Notice that the surface brightness of the clouds is the same regardless of the orientation of the filter. Unfortunately a polarisation filter can not be used to block out light pollution.
Seeing is believing. I recommend all of you to try this once.

Inge S

Please, don't take this personally, but wouldn't it be a better idea to post stuff about planets (even outside Pluto) and comets under the "Solar System Observing" forum?

Planets orbiting other stars, on the other hand, naturally belong to this forum. It is possible to detect transits of such planets with amateur equipment, and posts about this would be of great interest.

Inge S

Against all odds the sky cleared up yesterday evening, and the hard core of our local astronomy club deicded to go out observing. We used an 18-inch f/5 Dob with a Swayze mirror, and concentrated on a few objects.
Unfortunately M16 and M17 were blocked by clouds, but M11 was magnificent with low power (31mm Nagler). The sky background is richly populated with faint stars, but the cluster stands well out. I noticed very little colour in the cluster, but since it is so rich, it is very beautiful.
Next object on the list was M27 in Vulpecula. It is a grand object with this aperture, showing considerable structure, and several foreground (background?) stars. It was best at moderate power (16mm Nagler), and an O-III filter increased the amount of detail, particularly in the outer parts. It was interesting to notice "ears" in the SE/NW directions where I have not seen anything with smaller aperture.
The Veil complex is superb with this aperture. The 31mm Nagler/O-III combo showed an enormous detail in the filamentary structure already in the region near 52 Cygni. The middle part also showed many patches of nebulosity, and the eastern part of the loop was very bright and extremely detailed. Although the nice colours shown in many photos were absent, nothing compares with the direct view of this nebula through the eyepiece.
We were not able to see the central star of M57 in Lyra. Seeing was not perfect, and even with an 18-inch aperture this difficult to detect against the nebulous background.
We finished by observing the galaxies, M33 and M31. The spiral structure of M33 was evident at first glance and the spiral arms were decorated with emission regions. This galaxy would rank high on a list of the best objects for an 18-inch scope. The view of M31 was even more incredible. We were not prepared for a search for globulars, and thus we didn't really make out more details than can be glimpsed with smaller telescopes. However, with such an aperture the dust bands, the core and spiral arm segments are readily seen without straining the eyes. It is just to lean back and enjoy the view.


Inge S

I went out observing last Friday with a person who wanted to learn how to locate some good objects without needing any technical aid (BTW the owner of the 18-inch Dob which I sometimes have the pleasure to use). Two evenings earlier he demonstrated his ability to find M27, M57, M13 the Veil complex and, of course, the Andromeda Galaxy. This evening, we used my 12.5-inch Portaball, and went for some of the other good objects for this time of the year.
We started with the Saturn nebula, NGC7009. From our latitude this planetary is a bit low, but it was possible to make out the "Saturn" shape, and a greenish colour was obvious at a magnification of 167x.
Next we turned to M71 which is a nice cluster and quite easy to find from the Sagitta asterism. About eqally easy to locate is M56 using Beta Cygni and Beta Lyrae as reference stars. Both clusters are relatively well resolved in the 12.5 inch. A magnification of 167x is well suited for both clusters.
M2 is a bit more difficult to locate since the distance to the nearest bright stars is pretty long. I use Alpha and Beta Aquarii as reference stars, and imagine the cluster being near the top of an isosceles triangle with the two stars. My friend was surprised by the brightness and richness of this cluster, and wes even more impressed by M15. (We don't have access to the wonders of Sagittarius)
We then turned to some of the interesting nebulae of Cygnus. Pointing the telescope at the North America nebula isn't difficult. Seeing it in a telescope with a 1 degree field, however, may be pretty hard. However, the Mexico region stood quite well out with the O-III filter. While in this region we also observed the planetary, NGC7027 using Nu and Xi Cygni as guide stars. Maybe not an impressive object, but relatively easy to locate. More interesting is the blinking planetary, NGC6826. The blinking effect was quite obvious with the 167x magnification.
Strangely enough, my friend found the Crescent nebula more easy to see than the North America nebula. It is, indeed, much fainter. Its approximate position is relatively easy to find going from Gamma towards Beta Cygni. But the star field is extremely crowded, and the nebula is easily overlooked. It may be smart to use the O-III filter during the search. Our observing conditions were below average with clouds coming and going, but it was possible to make out quite some detail in the nebula.
Planetary nebulae are interesting since they come in a variety of sizes and shapes. We therefore also observed NGC6210 in Hercules (a bit difficult to find), M76 in Perseus (very easy to find) and bright NGC7662 in Andromeda which appears much bluer in colour than most other planetaries.
Finally we observed two objects in Cassiopeia, the great cluster, NGC7789 and the interesting nebula NGC281 with the fine multiple star, Burnham 1 in the centre. This nebula is difficult without a filter, and O-III works miracles on it.
Next evening when we are out with the 18-inch, I expect that my pupil will locate all these objects by himself. He plans to install digital setting circles, but still it is nice to be able to locate a few of the show objects without the assistance of a computer.

Inge S

We had excellent weather with clear transparent sky on Saturday, September 10th. A cloud bank over the ocean in the west was slowly approaching, but it was still clear at 10:30 pm, and therefore I went for an observing session. Arriving at my dark site I found the eastern sky partially blocked by semi-transparent clouds, and the northern sky was illuminated by auroral glow. In the south-west, however, the sky was dark and clear, and the temperature was pleasant, about +8 Centigrade.
This was one of my rare opportunities to observe some of the summer objects familiar to most of you, but very exotic to me. First target was M16 which I saw first time one year ago. The cluster itself is rather coarse, but the nebulous glow was obvious at first glance. With the O-III filter and 63x magnification, the nebula was very prominent, and the obscuring "fingers" could easily be seen. Last year I didn't notice them.
The way down to M17 was short. This nebula is very bright and detailed, but also with hints of fainter nebulosity outside the "swan" pattern (reminds me more of a duck, though). Great object!
Of course, I also observed M11, and afterwards turned to the nearby globular, NGC6712. Many stars were visible in this cluster superimposed on an unresolved glow. In the same field as the cluster the planetary, IC1295 could be seen. Without the O-III filter it was very faint, but with the filter the difference in brightness between the cluster and the nebula was very small. Of course, the nebula was considerably dimmed by the filter. To me the nebula appeared only slightly smaller than the cluster. Fine pair of objects, unfortunately very low in the sky from my location.
I observed many other objects this evening, both clusters, nebulae and double stars. I'll tell about the doubles in a separate post, and just mention one more of the DSO's, the open cluster, NGC6791 in Lyra. This cluster is extremely rich to be an open cluster, containing several hundred stars. First time I observed it I used 8 inches of aperture. It was then visible as a faint glow, rather large in extent (perhaps 15') but no stars were visible. With the 12.5-inch I'm still not sure that I can see any of the cluster's stars. There are some small stellar points superimposed on the glow, but these may as well be foreground stars. It woud be interesting to hear if anyone have observed it with larger aperture, or succeeded in resolving the cluster with a smaller scope. It is easy to locate, very near the wide double, Eta Lyrae.

Inge S

I suppose that most experienced observers agree that the darkness of the background sky strongly influences the chance of detecting detail in deep sky objects. Several factors contribute to the background brightness, the most annoying being scattered light from artificial light sources.
For Nordic residents auroral glow is another important factor. Even when no visible aurora is present, the radiation from the background is about twice as strong as from the tropics. I'm however a bit uncertain about whether the polar background radiation varies with the solar cycle. Do anyone know anything about this?
Another question: Is there any evidence about variation in background radiation (not related to light pollution) through the night? Is the morning better than the evening?

Inge S

Two of my astro-friends I have decided to make a one week's stay at the Canary Islands next May. We have made arrangements with a person who is specialising on astro tourism, and already paid for the flights and the stay. I'm going to take my 12.5-inch with me, but there will also be other scopes available.

I have never been so far to the south before (about 28 deg north), and I have to prepare well beforehand in order to have a successful trip.

In addition to Jupiter which will be well placed for observation at that time I have already put the following objects on my schedule:

Omega Centauri, NGC5128, M83, the Messier objects in Scorpius and Sagittarius, and doubles like Nu and Xi Scorpii.

The Virgo - Coma galaxies will, of course also be much higher in the sky than what I'm used to, and I look very much forward to M104.

Anything else in this part of the sky (Centaurus, Lupus, Scorpius, Saggitarius)that shouldn't be missed? I'm interested both in the show objects and some real challenges for my 12.5-inch.

Inge S

Yesterday night I observed some DSO's, double stars (cf. post about Gamma Andromedae - double star forum) and Mars together with Eckard Fuchs using his 18-inch Dob.
Among the deep-sky objects we observed the large, faint galaxy, NGC4236 in Draco and the distant, very rich, but faint open cluster, NGC6791 in Lyra.
We both agreed that the cluster was more difficult to detect than the galaxy.

What is your experience? What does it take to resolve NGC6791?

Inge S

Yesterday evening I made an observation that surprised me a bit. I went outside an hour or so after sunset. The sky background was still far from dark (dusk always lasts long at my latitude) but stars down to about 5th magnitude were readily visible. The moon was still very low and didn't contribute much.
Three hours later the influence of the sun, of course, was gone, but the moon was higher in the sky. At this time the sky appeared black, not blue, but the faintest stars were no longer visible. The limiting magnitude was now about 4.
I'm a bit puzzled about this. Why could I see more stars on the relatively light blue background at dusk than at the black bacground of the moonlit sky later at night? Was I somehow fooled by my dark adaptation? Is there a difference between sunlight scattered by the upper atmosphere and moonlight scattered by the lower? How important is the ambient light from the moonlit landscape?
If this was the only time I made this observation, I would hardly have mentioned it. But this seems to be a common phenomenon. Have anyone else made the same observation? Any idea why it is like this?

Inge S

Presumably double stars are randomly distributed through space. In spite of this I have a feeling that some parts of the sky have their lion's share of attractive double stars, while other parts have few doubles.
One of the reasons for my feeling may be that as a star hopper I favour either naked eye doubles or doubles that are relatively easy to locate. Maybe GOTO users have a different feeling. I also admit that I have a preference for doubles closer than 10", and particularly I enjoy pairs in the 1 - 3" range. Anyhow, here are my favourite constellations:
Orion: Many of the naked eye stars of this constellation are attractive doubles. And there is a multitude of fainter, very attractive pairs. Orion contains several multiple stars. The only minus could be that not many of the brighter doubles in Orion show any appreciable colour contrast.
Bootes: This is another constellation where a high number of the naked eye stars are doubles. Bootes also contains several relatively fast binaries.
Draco: Perhaps my favourite double star constellation. It is a treasure box for the hunter of moderately faint (6 - 7th magnitude) doubles. I have a long list of Draco doubles in my observation log, and still many interesting pairs on my "to do" list.
Lynx:This may be the constellation with the highest ratio between good doubles and naked eye stars. It may be difficult to find the way through Lynx, but in part of the constellation it is possible to hop between the double stars.

These are my four top favourites, but there are several runners-up. Cassiopeia, Cygnus and Cehpeus are rich in good doubles. So is Aries, and Taurus contains many, quite challenging pairs. Another good constellation is Hercules, and small Corona Borealis should not be forgotten.
On the other hand I find Ursa Major to contain relatively few good doubles taking its size into account. Of course Zeta and Xi are fine doubles, but I don't have many faint doubles from Ursa Major in my observation log. Maybe all the galaxies draw all the attention.

Inge S