- Telescope: William Optics FLT 110 mod with FT 3025
- Camera: Qhy 2pro mono
- Mount: Skywatcher EQ6 pro
- Ts finder 8x50 & Meade DSI 1 for guiding
- Location: Agios Panteleimon & Grammatiko-Attiki
Information about NGC 6992
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 (radio source W78, or Sharpless 103), a large but relatively faint
supernova remnant. The source supernova exploded some 5,000 to 8,000
years ago, and the remnants have since expanded to cover an area roughly
3 degrees in diameter (about 6 times the diameter, or 36 times the
area, of the full moon). The distance to the nebula is not precisely
known, but Far Ultraviolet Spectroscopic Explorer (FUSE) data supports a
distance of about 1,470 light-years.
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. This is also one of the largest, brightest features in the
x-ray sky.
The nebula was discovered on 1784 September 5 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 image 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,[8] that the shell is
visible only when viewed exactly edge-on, giving the shell the
appearance of a filament. 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 OIII filter (a 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 OIII filter shows the delicate lacework apparent in photographs,
and with an OIII filter almost any telescope could conceivably see this
nebula. Some argue that it can be seen without any optical aid except
an OIII filter held up to the eye.
The brighter segments of the
nebula have the New General Catalog designations NGC 6960, 6974, 6979,
6992, and 6995. The easiest segment to find is 6960, which runs behind
the naked eye star 52 Cygni. NGC 6992/5 are also relatively easy objects
on the eastern side of the loop. 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.
