Challenge Objects - September 2005
The September 2005 DSO challenge objects were written up by Andrew Durick (astro_south), John Bambury (ausastronomer) and Mike Salway (iceman). The CDC charts were compiled by Andrew Durick (astro_south). The lunar challenge was written by Rob Mcpaul-Browne (rmcpb).
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.
For a printer-friendly view of the page, click the print icon at the bottom of the page.
Galaxy - NGC6221 (..)
NGC 6221 is a barred spiral galaxy in Ara. It is very easy to find being quite close to the star Eta Ara. There is another nearby galaxy (NGC 6215) that has been shown to be interacting with NGC 6221 through the mapping of neutral hydrogen. The bridge of material formed between these galaxies is estimated at 100kpc given a likely "encounter" time between the galaxies of about half a billion years ago. The neutral hydrogen is not visible at the scope (so don't bother trying to look). Both these galaxies are easily visible with 6" (from dark skies) and they can both be seen in the same low power field of view.
For those with larger apertures (12" and up) you may be able to detect a spiral arm towards the north in NGC 6221 if you are at a dark site and spend some time looking. There has been supernova discovery in this galaxy (1990 by R. Evans) so while you are looking at it you may want to note the visible star patterns and confirm the stars later on with an older photograph or your planetarium software.
Open Cluster - M11 (Wild Duck Cluster)
M11 (also known as NGC6705, or the Wild Duck Cluster) is an open cluster in the constellation Scutum. It is a compact open cluster, often mistaken for a loose globular, made up of over 2000 stars, 500 of which are brighter than mag 14. The stars in the cluster all formed together, approximately 250 million years ago. It spans an area of sky approximately 14 arc minutes across.
The common name "Wild Duck Cluster" comes from its resemblance to a flock of wild ducks in flight, when viewed through a telescope. Do you see this?
M11 will be seen as a bright smudge in binoculars, and is a lovely object for scopes of all apertures. The cluster looks stunning in all powers, though I've found a medium power up to 100x gives the best view. If the seeing is good, magnifications of 150x or more will separate the cluster to show darker lanes between the stars. There is a bright mag 8 yellow star near the edge of the cluster that outshines the rest and appears to give real depth to the grouping.
Being in the plane of the milky way, the cluster is set among a stunning backdrop and is a sight not to be missed this month. M11 is one of the most beautiful open clusters in the sky, commonly observed and photographed and I'm looking forward to seeing many observing reports, sketches and images of this object taken by forum members.
Globular Cluster - NGC6752 (Pavo Glob)
NGC 6752 is also known as Caldwell 93 and is colloquially known as the "Pavo Glob". The globular was discovered in 1827 by James Dunlop. The apparent size of this globular is somewhat open to discussion, O'Meara lists it as 29' but most other reputable sources including Hartung and Burnham list it as 15'. The Central Core of NGC 6752 is very small and compressed and covers an apparent diameter of 2.5'. The stars external to the core extend outwards in looped arms and resemble a butterfly, somewhat more so in my opinion than M6 the Open Cluster so named.
NGC 6752 is one of over 20 Milky Way Globular Clusters which have undergone a "core collapse". NGC 6752 is one of the closest and brightest globulars to us and is one of the easiest to resolve in small telescopes. An attractive double star h 5085 is also included within the outliers. This was one of Hartungs' favourite targets and without doubt makes the top 10 globulars list, it is a wonderful target in any instrument over about 4" aperture.
Nebula - NGC6726 (Corona Australis Nebula)
NGC6726 is an intriguing object in the constellation of Corona Australis, and is usually catalogued with NGC6727, NGC6729 and IC4812. There is not a lot of information to be found on this object, classed both as an emission and a reflection nebula. There is also regions of dark nebula, all combining to block the light from the background milky way stars.
The reflection nebula is lit up by a few young bright stars in this dusty cloud, including the variable star R Corona Australis. There is stars being formed behind the dust and at 500 light years is one of the closest star forming regions to us.
A compact globular cluster, NGC6723, is found nearby though is catalogued in the constellation Sagittarius and is 30,000 light years distant, far beyond the dust cloud of Corona Australis.
I'll be interested in your reports of what eyepiece combination provides the best view for you, but imagine a low to medium power will be best to take in the whole region. It is also worth trying a narrowband filter to see if it enhances the view of the nebula. A dark sky will help with this one, so try to get your observations and images done early in the month while the moon is new.
Planetary Nebula - NGC6302 (Bug Nebula)
NGC 6302 is a planetary nebula near the "stinger" in the tail of the Scorpion. It is commonly referred to as the Bug Nebula, as the unusual shape of the planetary resembles the view of a squashed bug. It is one of the best examples of a bipolar nebula visible from our vantage point in the universe. Once bipolar planetary nebulas were considered rare, but it is now thought that the various shapes of planetary nebula can be traced back to a single shape and the various rings, butterflies and asymmetric lobes can be formed from a single object viewed from various directions. With the Bug we are seeing this shape perpendicular to the long axis.
The object is easy to find being ~4 degrees west of Lambda Scorpii. I look for an asterism of stars (as identified in the "zoomed" finder chart) of a slanted " I ". NGC 6302 is located where the fourth bright star would be to make up the longer crossbar. Interestingly, located at the opposing end of this asterism (on the other cross bar) is another planetary nebula - NGC 6337. This planetary is a ghostly ring that requires a bit of patience to locate and observe. Through my 12.5" dob it is bright enough to observe with direct vision although averted vision helps discern the ring nature - one of my favourites to observe.
The Bug Nebula can be glimpsed in small scopes, while the view through larger scopes will reveal much of the structure that is portrayed in photos. There is plenty on the web about NGC 6302, including Hubble (HST) photographs and chemical studies, which provide interesting background to observing this object.
Multiple Star - h 5003
H 5003 is not known by any other common names. It lies right on the Sagittarius/Scorpius border. It was first measured in 1836 by John Herschel. Like some of the earlier Monthly Observing Challenge (MOC) double stars it presents a lovely colour contrast, with a Mag 5.4 Yellow primary accompanied by a Mag 7.0 Blue/White Secondary. Separation is currently 5.8" making it easy to separate in the smallest telescopes with medium power (about 100x). Separation has decreased slightly from 6.20" in 1836 to its current separation of 5.8". The position angle (PA) of the secondary has remained unchanged over the same time period. Notwithstanding that not much has changed since 1836 the stars are believed to be a related pair.
The spectral types show the stars to be M1Ib (yellow-orange for the primary) and G8II (white-pale yellow) for the secondary. The visual colours I previously described and what I see, of yellow and blue is a little inconsistent with the spectral types but this is a common occurrence. What colours do you see? Both stars are quite small and bright and separation is nice and clean with the stars focusing to fine little pinpoints. The background field is very rich and almost open cluster like, with this beautiful little double set amongst it. There is also a 3rd component which is likely to be a field star. The "C" component is Mag 13.1 at PA 239º. Were you able to identify the "C" component?
This double will not be found in many of the databases in use by GOTO telescopes and Digital Setting Circles (DSC's) but it's well worth the hunt. It is included in Sky Commander's database.
The Hipparcos Star Catalogue Number is HIP 88060.
Lunar Challenge - Copernicus
Each month we will suggest a Lunar feature to observe. Basically, it will come from the Lunar 100, a list developed by Charles Wood for Sky and Telescope magazine. It lists 100 of the features found on the moon in order of difficulty to observe.
The September feature is the large crater Copernicus (#5 on the Lunar 100) which is a typical large complex crater found in the north-west quadrant of the moon. It is best observed 2 days after the first quarter or 1 day after the last quarter, where it will be on the terminator. It is a large feature approximately 95 km wide with a wall height of about 3800 metres and so is an easy target even in binoculars. It is approximately 800 million years old and is described as a young formation with a slightly hexagonal form having bright ejector rays all round, steep walls and three central mountains. This crater is remarkably well preserved and indicates that there has been little meteor activity since its formation as there are remarkably few craters formed within it. One notable exception is the double crater Fauth formed at the base of the north wall of Copernicus. It is about 12km wide, 20km long and about 2000 metres deep. Can you see it? I'd love to see your images of it.
While in the area take note of the Carpathian Mountains and the crater Eratosthenes which is best seen one day after the first quarter.
The following images are taken hand-held afocal by Rob McPaul-Browne.
General location - taken on day 9 of the lunar cycle
The following image also shows the ejecta rays, taken by Mike Salway with a ToUcam and a dob.
Ejecta rays - taken on the 1st Feb 2005.