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

Const.:

Fornax

Type:

Barred Spiral

Visual Mag.:

9.5

Finder Charts

RA:

3h 33.5m

DEC:

-36°8.3'

Wide

Diameter:

11x6'

Distance:

11 mpc

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Forum:

Reports and Sketches / Images

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)

Const.:

Puppis

Type:

Open Cluster

Visual Mag.:

6.0

Finder Charts

RA:

7h 41.8m

DEC:

-14°49'

Wide

Diameter:

27 arcmin

Distance:

5400 ly

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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.

8” Reflection:
Relatively easy to find, although close by M47 is some what more prominent though the finder scope. M46 is the fainter patch 01°16' slightly north of due west of M47. It is a reasonably large cluster more suited to low to medium powers. Obvious in the mix, is this months Planetary Nebula object NGC2438. I see easily 100+ plus stars rather loosely populated. With a total VM of 6 it should be an easy target for smaller aperture scopes. Rising around 9pm during the start of the month. It will be will better placed mid evening or midnight.

 


Globular Cluster - NGC362

Const.:

Tucana

Type:

Globular Cluster

Visual Mag.:

6.6

Finder Charts

RA:

1h 3.2m

DEC:

-70°51

Wide

Diameter:

12.9'

Distance:

~27,700 ly

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Reports & Sketches / Images

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)

Const.:

Orion

Type:

Diffuse Nebula

Visual Mag.:

8.3

Finder Charts

RA:

5h 46.7m

DEC:

-00°3'

Wide

Diameter:

8x6 arcmin

Distance:

~1600 ly

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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

Const.:

Aquarius

Type:

Planetary Nebula

Visual Mag.:

10.8

Finder Charts

RA:

7h 41.8m

DEC:

-14°44'

Wide

Diameter:

> 1.1'

Distance:

2900 ly

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Forum:

Reports & Sketches / Images

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:

  1. The radial velocity of NGC 2438 is about 77 km/sec recession, which is 43 km/sec different from the cluster's value and would not allow the cluster to hold it, even if it were at the same distance. Woldemar Götz, however, gives derived distances of 4,600 light years for the cluster and only about 2,900 light years for the nebula, which would mean that the planetary is a foreground object.
  2. Planetary nebulae are only visible for short times and fade quickly; most of them are visible only for a few 10,000s of years before their material has volatilized into the surrounding interstellar space.
  3. Planetary nebula are late states in stellar evolution, which occur only for comparatively low mass stars of less then 3 solar masses. These stars, however, need more than a billion years for their evolution until they eject their envelope to form the planetary, which is much longer than the age of M46 (more massive stars "go supernova"). However, this last argument is questionable, because some young clusters as the Pleiades (M45) contain a significant number of white dwarfs, which must have evolved from more massive stars; these stars must have lost most of their mass during their evolution, probably in the form of strong stellar winds in their Red Giant phase, and must have gone through a planetary nebula phase.

8” Reflection:
This object is probably better suited to 6”+ scopes, although I couldn’t imagine it would be an impossibility in smaller apertures. A spectacular object sitting within the field of M46 as though secretly hiding out. Good for low and high powers. At higher powers I see some mottling to the nebulous envelope with the benefit of a UHC filter. Rising around 9pm during the start of the month it will be will better placed mid evening or midnight.

 


Multiple Star - Sigma Orionis

Const.:

Orion

Type:

Multiple Star

Visual Mag.:

3.7

Finder Charts

RA:

5h 38.7m

DEC:

-2º36'0"

Wide 

Separation:

various

Distance:

1150 ly

Zoom 

Forum:

Reports & Sketches / Images

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

Type:

-

Lunar 100:

-

Size:

-

Best Viewed:

Days 5, 6, 18 and 19 of the lunar cycle

Forum:

Reports & Sketches / Images

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.

The features:

  • Starting with the Theophilus Triplet to the south of Mare Tranquillitatis which is a spectacular set of three craters:
    • Catharina – The oldest in the set is a 100km diameter impact crater with heavily degraded walls (virtually no terracing left) and many craterlets across the floor. The northern section of the wall is overlain with a 50km crater Catharina P. This crater is named after the Christian martyr Sainte Catherine d’Alexandrie who was beheaded in 307AD on Emperor Maxene’s orders.
    • Cyrillus – Is a 100km crater with high walls that still retain some terracing. There is a 17km craterlet in the western wall and the northern wall is crushed by Theophilus. It contains a 1000m central mountain and a curved rille on the crater floor. This crater is named after the 5th century Greek philosopher Saint Cyrille.
    • Theophilus – The youngest crater of the triplet as it overlays Cyrillus and has well preserved 5000m walls with landslips to the south. It contains a central mountain range of four main peaks to 2000m high. Three of these peaks form a chain with the height decreasing progressively. This crater is named after the 4th century Greek philosopher Theophilus.
  • To the north of Mare Serenitatis we have another set of three prominent craters:
    • Aristoteles – An 87km crater with 3700m terraced walls and landslips to on the southern wall. It exhibits prominent rays as does Copernicus but they are not so visually striking due to the oblique angle at which we view them because of the latitude of the crater. It has two modest central summits to 500m and many craterlets across the floor. This crater is named after Aristote a 4th century BC Greek philosopher who was a tutor to Alexander the Great.
    • Eudoxus – to the south of Aristoteles is a 67km crater with degraded walls indicating it is older than Aristoteles. It has many craterlets on the walls as well as the crater floor again, indicating great age. It is named after the 4th century BC Greek astronomer Eudoxe who was the inventor of the 365.25 day year we still use today.
    • Alexander – an extremely old crater which is described as a completely wrecked formation. It was heavily damaged by the formation of Eudoxus and its floor has been flooded with lava. It is surrounded to the west by the Caucasus Mountains, a large range covering 100x500km with peaks to 3500m and deep valleys. This crater is named after the 4th century BC Macedonian king Alexandre le Grand.

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!!



 

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