The summer constellation Cygnus (the Swan) graces a rich trail of stars comprising the disk of our galaxy, the Milky Way. In a truly dark sky, a peppering of faint stars, ranging from bright sparklers to a continuum of stellar points too small to be resolved, make even naked-eye astronomy of the region a deeply-rewarding experience.

However, the power of a good telescope, employing a contrast-enhancing nebular filter, will penetrate deep into the silken threads of the "Veil" nebulae. From discovery by Sir William Herschel, until the introduction of nebular filters, the faint visual trace of the two brightest sections of the "Veil" were only to be seen in pale, ghostly views.

"The Great Cygnus Loop", nearly 3 degrees in diameter, comprises an expanding cloud of hot interstellar matter, thrown off by a supernova that occurred perhaps 50,000 years ago. Deep photographs reveal that the cloud seems to surround a fairly vacuous internal cavity; a dusty outer shell causes a noticeable dimming of regional starlight. The red of doubly ionized hydrogen gas, which shows up in a color image (such as these wonderful pictures by Chuck Vaughn) is too faint to be perceived by the telescopic eye, which sees only shades of light and dark.

In the days before manmade light pollution, the "Veil" could be seen in short-focus comet-catchers or with binoculars. However, a night sky with a naked-eye stellar limit as faint as even 6th magnitude will degrade the contrast so that the "Veil" may not always be spotted, not even in the finderscope! If your low-power finder uses standard eyepieces, try adding a hydrogen-nebula filter.

In moderate to large-aperture scopes, using a hydrogen- or oxygen- line narrow bandpass nebular filter, the diaphanous network of luminous strands of the two major sections of the "Veil" are clearly seen in a fairly dark sky, using a large eyepiece exit pupil. In 1995, the author had the opportunity of close comparative examination with 4" f/4 richest-field, 8" f/5.2 Newtonian, and 17.5" Dobsonian instruments. The "Veil" was visible in all three; almost the entire "Cygnus Loop" could be followed in the big Dobsonian. The western portion (NGC-6960), nearly bisecting the star 52 Cygni, is less dense than the eastern part (NCG-6992, imaged in this program). In the 4" and 8" scopes, the latter seemed to have a uniform, milky surface, while in the 17.5" it was resolved into a tangled skein of filaments; without the nebular filter the "Veil" virtually disappeared!

The esteemed Northern California amateur astrophotographer Chuck Vaughn used a Celestron C-14 scope telecompressed to f/7, with Kodak Tech-Pan 2415 film, processed with gas-hypersensitization, and a Cassegrain guider during a 1 hour exposure. The photograph was so rich with nebulosity that heavy processing was necessary to simulate a vaguer eyepiece-view.

PICTURE 1 (left): NGC-6992, simulating a 12-17" inch scope representation (low magnification of 35-60X), under a sky with a naked-eye stellar limit of about 5.9 magnitude. The "Veil" is barely detectable without a filter.

PICTURE 2 (middle): By adding a narrowband nebular bandpass filter, which attenuates unwanted light wavelengths, one may clearly see the structure of the "Veil", with a very dark sky background. While the filter increases nebular contrast by removing some background light pollution, some of the fainter stars will be dimmed quite noticeably by the filter's narrow bandwidth response.

PICTURE NO. 3 (right): A larger section of the "Veil" from the original print. It is practically impossible to see as much contrast as shown in this deep exposure when viewing the object by eye with an amateur-sized telescope!