Seeing the Veil August 17, 2007Posted by dorigo in astronomy, personal, science.
Yesterday evening the sky above the Dolomites did not promise anything good. Scattered low clouds, little wind, and high humidity were telling me I would have rather watched TV than carry my telescope to some remote place in the hope of observing the sky’s wonders, ending up staring at steady clouds. What was making me even more gloomy were the forecasts and the numerical simulations of cloudiness above northern Italy, which concurred in predicting a disturbed night.
But I had an obligation. Mauro, current director of the Mechanical Engineering department at the Trento University and fellow galaxy chaser, was determined to give the night a try, having been unable to observe from a dark site during the last couple of weeks, and with only a few days before the moon would start to prevent deep sky observations. He was leaving from his home near Venice, driving two straight hours to get to our favourite observing site, Casera Razzo – a place near Sella di Ciampigotto, 1800 meters above sea level and at least 10 kilometers from the nearest city lights.
So I wearily packed my telescope in my car. My equipment for an observing night with the 16″ dobsonian scope consists in a 2’x2’x2′ wooden box with the mirror housing, the rails, and the base, another 20″x20″x3″ wooden box where the mirror is stored for transportation, a long box with eight aluminum poles and hardware bits, plus the 18″x10″ cylindrical upper cell with the secondary mirror and focuser. Then there is a 24-hour suitcase where I store my eyepieces, the finder scope, and other miscellaneous stuff, and finally a bag with a pair of binoculars, my laptop, and a book or two. I am pretty well organized these days, so packing the stuff in the car takes only about 10 minutes, but it involves some wrestling with cumbersome pieces down the steep ladder leading out of our apartment…
And so, as dusk turned into night, I drove to Casera Razzo. 45 kilometers of mountainous roads. I drove with little hope, but by the time I got to the site a wonderful milky way was there to greet me. But it did not last long: low clouds encircled the site, until only a star here or there was punching through.
Mauro arrived late -no surprise-, and as he saw the messy sky he suggested to move to another site only a couple of miles away. His theory was that warmer air from the valley below was rising to the plain of Sella Ciampigotto, then pouring down into clouds as it found colder temperatures.
And he was right! As we settled and started to mount my dobsonian scope, I could see the clouds low to the west, but the sky above us was perfect, dark and clean, with a limiting magnitude of 6.5. Wonderful!
We observed many faint galaxies, as our agenda dictated. But the Veil Nebula – a complex mesh of filaments spanning more than three degrees of sky in Cygnus, the remnants of one or possibly two supernovae exploded 15,000 years ago – was too inviting to not give it a look.
The Veil is cataloged as a series of distinct nebulous objects – NGC 6960, 6979,6992, 6995. It is located at about 2,500 light years from us, and its integrated visual magnitude is about 5, but I have never heard anybody claiming to have seen it with unaided eyes, although theorically possible: the object is projected against a background thick with milky way stars, and it is quite extended.
Now, I had seen the nebula with my 16″ dobsonian scope under similarly dark skies bafore. But I had never had the opportunity to look at it through a O-III filter – a filter that selects the doubly-ionized Oxygen emission lines at 4959 and 5007 angstrom of the nebula, cutting away almost everything else. Mauro provided the filter, I framed NGC6960 (the eastern end of the ring, close to 52 Cygni) in the finder, moved to the eyepiece, and my jaw dropped! Not only did the filter enhance the tenuous luminosity of the nebula, making it jump out of the eyepiece. It also revealed tiny filamentary details which I had only seen in the very best long-exposure pictures of the subject. I was amazed.
On the left you can see a wide field SDSS picture of the complex nebula. It consists in a ring broken in several points, almost circular in shape, to which is added another arch, incomplete and almost intersecating with the first.
I am always wary when people tell me they see color in bright nebulae observed with telescopes – the human eye does not recognize it well enough in objects below a certain surface luminosity. However, with the filter the nebula seemed to have been stripped off any color at all. It shone with a cold silvery gray, almost metallic. That is the price to pay for an observation with narrow band filters such as the O-III.
Below is another image of a small part of the object – this time in color, and taken with the Hubble. Believe me, the amount of detail of the intricate wisps of this picture does not make me envious – the view through an amateur scope with dark skies and the proper filter can raise your hair just as much. I now understand why some vote the Veil Nebula the most beautiful object in the sky.