Challenge Objects - May 2005
The May 2005 challenge objects and CDC charts were compiled by Andrew Durick (astro_south). Nebula suggestion by Mike Salway (iceman). Double/Multiple star suggestion and text by John Bambury (ausastronomer). All other objects and text by Andrew.
Scroll down to see each of the objects, and click on the links to download the finder chart or view the forum threads related to each object.
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Galaxy - M104 (Sombrero)
More commonly know as the Sombrero Galaxy, NGC4594 is object 104 in Messier’s list of objects. It is a reasonably bright spiral galaxy that we see edge on from our vantage point and probably provides the best (and easiest to detect) dark lane of any edgewise spiral galaxy.
It gets its name (Sombrero) from its appearance in long exposure photos, although with moderate to large apertures the major features are easily visible in the eyepiece and approach what is seen in photos. In small apertures the dust lane can be glimpsed, and Scotty Houston recommends the use of dark cloth to cover your head to block stray light from entering the side of your eye – a hint you could employ for other faint targets. A 4” can pick out the dark lane, but it takes a bit of effort and obviously dark skies. The presence of this dark lane can be inferred in small scopes due to the shape of the glow. In larger apertures the glow below the dark lane gives it a “3d” appearance. The brightening of the core of this galaxy to one side of the dark lane also adds to the 3d effect at the eyepiece. What can you see?
The galaxy is located in Virgo, though it is easier to navigate to from Corvus. While on your way, check out the nearby “Stargate” asterism – one smaller triangle inside another as it is likely to be one of the stepping stones
Open Cluster - IC2602 (Southern Pleiades)
IC 2602 is an open cluster located in the constellation of Carina. It is more commonly known as the "Southern Pleiades" due to its similarities to the Pleiades cluster in Taurus. It is also known as the Theta (q) Carina Cluster, as it contains the 2.8mag Theta Carina as the brightest star in the cluster.
The remaining components are 5th magnitude and fainter. The cluster covers a full degree of sky and includes at least 60 members, of which 30 are above 9th magnitude.
Some of the clusters members (as with the Pleiades) are resolvable with the naked eye – how many can you count? The cluster is best viewed through binoculars or a rich field telescope. It is located south of the Eta Carina Nebula as is demonstrated in the finder chart.
Globular Cluster - NGC2808
NGC 2808 is a fine example of a symmetrical and strongly compressed globular cluster.
Its component 13 to 15 magnitude members start to resolve in a 6” scope, smaller apertures will show it as a “bright nebulous haze” with “strong central condensation”. The object can be viewed in binoculars and I can see it as a “small blob” in my 6x30 finder.
Nebula - NGC2359 (Thors Helmet)
NGC2359 is more commonly known as Thors Helmet, as this is readily apparent from long exposure photographs. It is also commonly called the Duck Nebula but I’m not sure I see the duck shape. I have seen the telescopic view referred to as a rabbit, and this I can see.
The nebula is a Wolf-Rayet nebula and is caused by the expulsion of gas and dust from a massive blue giant star (HD56925) at high velocities (millions of km per hour). The high velocity stellar winds associated ionise the gases resulting in the features that glow so beautifully. Visually the object is a tough one and aperture does help. Recently on the “Starrynights” mailing list comments about the visibility of the nebula said it was detectable down to 4”, but requires a very dark site – certainly one to save for the new moon. The other comments were the that the image was ordinary until either a UHC or OIII filter was employed, then the nebula came alive with detail. I anticipate hearing about the view with and without from those with relevant filters.
I'd suggest this one be tackled early in the month, and early in the evening. Canis Major is setting fast, and if you don't get to it early it will be low on the horizon and hard to view. It may be the last chance you get to view it this year!
Planetary Nebula - NGC3242 (Ghost of Jupiter)
NGC3242 is a bright planetary nebula located in the constellation of Hydra. It is reasonably bright (7.8 visual magnitude) and can be detected in small scopes. It has the common nickname of the “Ghost of Jupiter” due mostly to its size.
At low power the nebula looks like an evenly illuminated glowing disk. It is not perfectly round and has been described as a “bluish egg”, though some people see it as a grey or pale green – what colour can you detect?
Obviously the larger the aperture, the more that can be seen, and the challenge here is to pick out the central “eye” structure that surrounds the central star. This inner ring has in very recent times given the nebula another nickname of the “CBS Eye” or “eye” nebula. The eye structure is only marginally brighter than the background disk (ie the brightness difference is very subtle) so it takes a little bit of effort to pull this out. I haven’t read this anywhere, but I find that if you slowly rack the focuser in and out it sometimes it just pops into view (obviously focus is critical). Some apertures won’t show this “eye” feature and it will be interesting to see how small an aperture this feature can be detected. It will be seen in a 30cm (12”) scope, but below this we will have to see.
A UHC or OIII filter will work well with this object. This is a good object for testing out the “blinking” method – whereby the filter is not attached to the eyepiece, but rather in your fingers it is moved in and out of the light path between your eye and the eyepiece (helps if your eyepiece has long eye relief so there is room for the filter and fingers). Obviously a dark sky helps this object, however it will still be visible in the suburbs and doesn’t require a moonless night.
Multiple Star - X Velorum (Dunlop 95)
x Velorum is one of the most aesthetically pleasing multiple stars in the entire sky. Andrew James from the ASNSW has nicknamed it Albireo Australis after its visual resemblance to the famous northern hemisphere double, Albireo (B Cygni).
x Velorum is in fact a triple star, the brighter AB components (mag 4.4/6.0, sep 51.7”, pa 105 deg), are also known as Dunlop 95. The third member of the trio is found 20.1” from the B component at pa 174 deg and is mag 12.1. This system is known as HJ 4341 BC (Herschel). The C component is more difficult to spot in smaller scopes than the two main components, which can be separated in larger binoculars. x Velorum presents a wonderful target in any sized telescope at low to medium powers. The two main components provide a brilliant colour contrast double of electric blue and a deep gold, with the colour contrast enhanced by the brightness of both stars. This wonderful target is not listed as a target of note in much of the literature, including Hartung’s Astronomical Objects for Southern Telescopes (Burnham’s Celestial Handbook does include it, albeit as a listing only). In the Hipparcos Catalogue it is listed as HIP 52154 and in the Tycho Catalog as TYC8605-1196-1
The proper motion of the trio indicates them to be a long period related system. A wonderful target to be returned to time and again.