Imaged on nights of 7/5/2021, 7/7/2021, 7/8/2021, 7/9/2021, 7/12/2021, 7/15/2021
Unguided
No Dithering
This 4 panel mosaic of the entire Veil Nebula was a challenge to process, but should not have been. I had a fine collection of subs where all 4 panels when processed to the RGB stage were really well matched. The way I did this which works really well is to only take subs on a panel for 20 minutes, then shift to the next panel, covering all 4 panels every 80 minutes. This produces over several nights of imaging a very uniform set of 4 panels, which should make it easy to assemble the panels without obvious differences. I reversed the order of panels a couple of times to further randomize the subs.
This process worked perfectly for the initial pairing of 1 and 2 on the left side, then 3 and 4 on the right side. They both looked close to perfect. I used the new Photometric Mosaic process, which worked really well on both the left and right sides. Both looked perfect with no visible differences top to bottom.
However, I could not get it to work well for the final merge of the left and right sides, even though the two sides visibly matched perfectly, each having the same nice color balance and intensity levels. The result after merging them always had one side that looked like the original, and the other side with a badly out of whack color balance, usually a strong red.
I finally gave up using Photometric Mosaic for this final merge and used the older GradientMergeMosaic, which worked fine. Interestingly, it did not work well at all for the left and right side prior stage merges. Go figure. If anyone knows what I might have done wrong with the settings for the Photometric Mosaic, I would love to get your help.
The Veil Nebula is a favorite target for many. It's one I must do with every new scope/camera I acquire. However, this is the first version I have ever done of the entire Veil, since my equipment requires a 4 panel mosaic.
There are really an impressive number of stars in this image. I count 544,371. Wow!
Wikipedia:
The Veil Nebula is a cloud of heated and ionized gas and dust in the constellation Cygnus.
It constitutes the visible portions of the Cygnus Loop, a supernova remnant, many portions of which have acquired their own individual names and catalogue identifiers. The source supernova was a star 20 times more massive than the Sun which exploded between 10,000 and 20,000 years ago. At the time of explosion, the supernova would have appeared brighter than Venus in the sky, and visible in daytime. The remnants have since expanded to cover an area of the sky roughly 3 degrees in diameter (about 6 times the diameter, and 36 times the area, of the full Moon). While previous distance estimates have ranged from 1200 to 5800 light-years, a recent determination of 2400 light-years is based on direct astrometric measurements. (The distance estimates affect also the estimates of size and age.)
The Hubble Space Telescope captured several images of the nebula. The analysis of the emissions from the nebula indicate the presence of oxygen, sulfur, and hydrogen. The Cygnus Loop is also a strong emitter of radio waves and x-rays.
The nebula was discovered on 5 September 1784 by William Herschel. He described the western end of the nebula as "Extended; passes thro' 52 Cygni... near 2 degree in length", and described the eastern end as "Branching nebulosity ... The following part divides into several streams uniting again towards the south."
When finely resolved, some parts of the nebula appear to be rope-like filaments. The standard explanation is that the shock waves are so thin, less than one part in 50,000 of the radius, that the shell is visible only when viewed exactly edge-on, giving the shell the appearance of a filament. At the estimated distance of 2400 light-years, the nebula has a radius of 65 light-years (a diameter of 130 light-years). The thickness of each filament is 1?50,000th of the radius, or about 4 billion miles, roughly the distance from Earth to Pluto. Undulations in the surface of the shell lead to multiple filamentary images, which appear to be intertwined.
Even though the nebula has a relatively bright integrated magnitude of 7, it is spread over so large an area that the surface brightness is quite low, so the nebula is notorious among astronomers as being difficult to see. However, an observer can see the nebula clearly in a telescope using an O-III astronomical filter isolating the wavelength of light from doubly ionized oxygen), as almost all light from this nebula is emitted at this wavelength. An 8-inch (200 mm) telescope equipped with an O-III filter shows the delicate lacework apparent in photographs. Smaller telescopes with an O-III filter can show the nebula as well, and some argue that it can be seen without any optical aid except an O-III filter held up to the eye.
The brighter segments of the nebula have the New General Catalogue designations NGC 6960, 6974, 6979, 6992, and 6995. The easiest segment to find is 6960, which runs behind 52 Cygni, a star that can be seen with the naked eye. NGC 6992 & 6995 are objects on the eastern side of the loop which are also relatively easy to see. NGC 6974 and NGC 6979 are visible as knots in an area of nebulosity along the northern rim. Pickering's Triangle is much fainter, and has no NGC number (though 6979 is occasionally used to refer to it). It was discovered photographically in 1904 by Williamina Fleming (after the New General Catalogue was published), but credit went to Edward Charles Pickering, the director of her observatory, as was the custom of the day.
The Veil Nebula is expanding at a velocity of about 1.5 million kilometers per hour. Using images taken by the Hubble Space Telescope between 1997 and 2015, the expansion of the Veil Nebula has been directly observed.
My Collections:
Abell Planetary Nebulae (Complete)Planetary NebulaeGalaxiesSharpless 2 Objects
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