Challenge Objects - December 2005
The December 2005 DSO challenge objects were written up by Rob Charteris (xrekcor), Andrwe Durick, Mike Salway and John Bambury (ausastronomer). 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 - NGC1365
NGC 1365 is one of the finest barred spiral galaxy in the southern skies. There is currently conjecture about its involvement with the Fornax Galaxy Cluster. It is thought to be closer to us than the cluster, however it shares redshift values with the cluster members.
This galaxy is a well known Seyfert Galaxy and has an intricate structure with a massive straight bar and two pronounced spiral arms.
In bigger apertures these arms take on a very “sharp” appearance, producing a resemblance to some sort of Ninja star weapon (well that’s what I see it as). I have seen the spiral arms of this galaxy through a 8” newt (where they appeared with mostly averted vision) through to seeing the distinctive and sharp arms through a 30” dob – very nice!
While in the area be sure to check out the nearby Fornax Galaxy cluster where you can see many galaxies in the one eyepiece view. Wander around with your lowest power and see how many you can fit into the view.
Open Cluster - M46 (NGC2437)
This rather splendid cluster is very rich, with 150 stars of mag 10-13 and probably a total population of over 500. The brightest of these stars are of spectral type A0, and each about 100 times more luminous than the Sun (the brightest is of apparent magnitude 8.7). This indicates an age of about 300 million years. The members are scattered over an angular diameter of about 27', corresponding to a linear extension of 30 light years at the cluster's distance of 5,400 light years, and are receding from us at 41.4 km/sec, according to Baade. M46 is classified as of Trumpler type II,2,r.
Discovered in 1771 by Charles Messier. M46 was the first object Charles Messier discovered after he had published the first edition of his list (M1-M45). He added this one to his catalog on February 19, 1771, three days after presenting it to the academy, together with three more Messier objects, M47, M48, and M49. Contained in the field of M46 is this months Planetary Neb NGC 2438.
Globular Cluster - NGC362
NGC362 is the “other” brilliant globular cluster in Tucana, and was discovered by James Dunlop on August 1, 1826 and cataloged by him as No. 62 of his catalog.
In the late 1980s, NGC 362 was compared to the otherwise similar globular NGC 288, and it was found that this cluster was about 3 billion years younger. This result was found because of differences in the color-magnitude diagrams: The so-called Horizontal Branch of NGC 362 is redder, and the turnoff point of the main sequence (hottest/bluest/most massive main sequence stars) is bluer (and brighter).
NGC362 is often overlooked because it’s in the same area of sky as it’s brilliant big cousin, 47Tuc (NGC104). However NGC362 has a lot of appeal in its own right, as a small compact globular cluster easily visible in small scopes, but with large apertures the globular is more resolved, revealing many stars tight to the core. The globular is also visible as a small fuzzy blob in binoculars.
When surfing around the SMC and Tucana, don’t just go to 47Tuc and move on. Make sure you spend visit NGC362 as it’s a brilliant small globular worth spending some time on.
Here is a brilliant image of NGC362 by Steve Crouch from Canberra.
Nebula - M78 (NGC2068)
M78 is the brightest diffuse reflection nebula in the sky. Discovered by Pierre Méchain in early 1780, Charles Messier added it to his catalog on December 17, 1780. It belongs to the Orion complex, a large cloud of gas and dust centered on the Orion Nebula M42/M43, and is about 1,600 light years distant. It is the brightest portion of a vast dust cloud which includes NGC 2071, NGC 2067, and very faint NGC 2064. Together with some other nebulae, including NGC 2024 (Orion B) near Zeta Orionis (sometimes called the Flame Nebula), all these nebulae are associated with the molecular cloud LDN 1630 (from Lynds' Catalogue of Dark Nebula), a part of the Orion complex.
M78 is not difficult to locate from Zeta Orionis, also named Alnitak, the easternmost star of Orion's Belt; M78 is situated about 2 degrees north and 1 1/2 degrees east of this star; a chain of 3 stars of mag 5..6, northward from Zeta, may help locating it. Alternatively, it is found roughly 1/2 deg North and 3 3/4 deg East of Delta Orionis, the NW most belt star.
Visually, M78 resembles a faint comet. It is just visible in binoculars under good conditions, as a very dim patch. Small telescopes already show it remarkably bright, and reveal the two illuminating stars, lying North preceding (NW) and South following (SE) like a double nucleus in the compact "comet head" part of M78; suggestions of a short and broad "tail" appear to reach to the South preceding (SW) end. The other nebulae in this field require a very dark sky and are much more difficult to see than M78; under very good conditions, a 4-inch can reveal NGC 2071, and suggestions of haze around M78. Stars are fewer to the west, an indication that in this region dark nebulae seem to obscure the stellar background. About 1 3/4 deg East of M78, open cluster NGC 2112 is found; this cluster is of about 9th mag and 11' in diameter, lies behind M78 at a distance of about 2800 light-years, and is much older: Estimated at about 2 billion years.
The best time to observe the nebula is later in the month (and later in the night) when Orion is overhead.
Planetary Nebula - NGC2438
Planetary nebula NGC 2438 is one of the discoveries of William Herschel, who cataloged it as H IV.39. The central star of NGC 2438 is of magnitude 17.5 and exhibits a continuous spectrum. William Herschel Discovered it in 1786.
Known as a special and famous feature of M46, NGC 2438 sits within the apparent borders of M46, which is also this month open cluster object. NGC 2438 appears to lie near the northern fringes of the cluster, although it is certainly no member of the cluster or perhaps a passing "guest", because of three reasons:
Multiple Star - Sigma Orionis
Sigma Orionis is also known as ADS 4241. Orion is possibly the richest of all constellations in Deep Sky Wonders and many hardened observers regard Sigma Orionis as its greatest treasure. To the naked eye Sigma Orionis appears as a single blue white star of Mag 3.7. In binoculars a blue white companion of Mag 6.6 can be glimpsed making the star appear as a double.
In small to medium telescopes its true beauty is revealed. The primary appears as a blue white star spectral type B3V (blue dwarf). The three secondary components visible in amateur telescopes are C (Mag 8.8 separation 11.5” pa 238°), D (Mag 6.6 separation 12.7” pa 84° and E (Mag 6.3 separation 41.5” pa 62°). The primary star is itself a close double; however the secondary with a separation of only .3” is not visible in amateur telescopes.
If the above isn’t enough to keep you happy 3’30” north west of Sigma Orionis is Struve 761 which is another multiple system of four stars. The four components of Struve 761 range in magnitude from 7.86 to 8.55 with separations ranging from 8.9” to 72” hence all are visible and resolved in small telescopes.
The overall visual effect of Sigma Orionis and Struve 761 is that reminiscent of a planetary system with a bright star surrounded by all these small dimmer stars.
A true jewel in the sky, which can be enjoyed in a telescope of any size.
The Hipparcos Catalogue Number for Sigma Orionis is HIP 26549.
Lunar Challenge - Days 5 and 6
This month we will take a look at some of the features visible on days 5 and 6 of the lunar cycle. Of course these features will be again on the terminator on days 18 and 19 with the sun setting in this case casting the shadows in the opposite direction to the earlier views. It would be worth comparing the views at both ends of the cycle but you will have to be keen as the moon dies not rise till about 11:30pm on day 18.
Enough rambling, the features selected this month are indicated on the afocal photo attached to this article and I’m sure that someone with even moderate equipment will be able to achieve a better result. One problem I encountered was taking the shot in the twilight as clouds were closing in and I had no choice, hence the lack of contrast in the shot.
Try observing and either photographing or drawing these features on the nights noted and observe the differing views of the features due to the rising and setting sun shadows. An image showing the location of the features can be seen here.
We look forward to your photos or drawings, have a go!!